Transact-SQL® User’s Guide Adaptive Server® Enterprise 12.5.

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Transact-SQL® User’s Guide Adaptive Server® Enterprise 12.5.1DOCUMENT ID: DC32300-01-1251-01 LAST REVISED: August 2003 Copyright © 1989-2003 by Sybase, Inc. All rights reserved. This publication pertains to Sybase software and to any subsequent release until otherwise indicated in new editions or technical notes. Information in this document is subject to change without notice. The software described herein is furnished under a license agreement, and it may be used or copied only in accordance with the terms of that agreement. To order additional documents, U.S. and Canadian customers should call Customer Fulfillment at (800) 685-8225, fax (617) 229-9845. Customers in other countries with a U.S. license agreement may contact Customer Fulfillment via the above fax number. All other international customers should contact their Sybase subsidiary or local distributor. Upgrades are provided only at regularly scheduled software release dates. 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Sybase, Inc., One Sybase Drive, Dublin, CA 94568.Contents Transact-SQL User’s Guide iii About This Book ......................................................................................................................... xix CHAPTER 1 SQL Building Blocks....................................................................... 1 SQL in Adaptive Server.................................................................... 1 Queries, data modification, and commands .............................. 2 Tables, columns, and rows........................................................ 3 The relational operations ........................................................... 3 Compiled objects ....................................................................... 4 Naming conventions......................................................................... 6 SQL data characters ................................................................. 7 SQL language characters.......................................................... 7 Identifiers ................................................................................... 7 Expressions in Adaptive Server ..................................................... 13 Arithmetic and character expressions ..................................... 13 Relational and logical expressions .......................................... 19 Transact-SQL extensions............................................................... 20 The compute clause ................................................................ 21 Control-of-flow language ......................................................... 21 Stored procedures ................................................................... 21 Extended stored procedures ................................................... 22 Triggers ................................................................................... 23 Defaults and rules ................................................................... 23 Error handling and set options ................................................ 23 Additional Adaptive Server extensions to SQL........................ 25 Compliance to ANSI standards ...................................................... 26 Federal Information Processing Standards (FIPS) flagger...... 27 Chained transactions and isolation levels ............................... 28 Identifiers ................................................................................. 28 SQL standard-style comments ................................................ 28 Right truncation of character strings........................................ 29 Permissions required for update and delete statements ......... 29 Arithmetic errors ...................................................................... 29 Synonymous keywords ........................................................... 30 Treatment of nulls.................................................................... 30Contents iv Adaptive Server Enterprise Adaptive Server login accounts...................................................... 31 Group membership.................................................................. 31 Role membership .................................................................... 32 Getting information about your Adaptive Server account........ 32 Changing your password......................................................... 33 Understanding remote logins .................................................. 34 How to use Transact-SQL with the isql utility................................. 35 Default databases ................................................................... 36 Using network-based security services with isql ..................... 37 Logging out of isql ................................................................... 37 Using the pubs2 and pubs3 sample databases ............................. 37 What is in the sample databases? .......................................... 38 CHAPTER 2 Queries: Selecting Data from a Table .......................................... 41 What are queries?.......................................................................... 41 select syntax............................................................................ 42 Choosing columns: the select clause............................................. 44 Choosing all columns: select * ............................................... 44 Choosing specific columns...................................................... 45 Rearranging the order of columns........................................... 45 Renaming columns in query results ........................................ 46 Expressions............................................................................. 47 Selecting text and image values.............................................. 53 Select list summary ................................................................. 55 Eliminating duplicate query results with distinct ............................. 55 Specifying tables: the from clause ................................................. 57 Selecting rows: the where clause................................................... 58 Comparison operators............................................................. 59 Ranges (between and not between) ....................................... 61 Lists (in and not in) .................................................................. 62 Pattern matching ............................................................................ 65 Matching character strings: like............................................... 65 Character strings and quotation marks ................................... 71 “Unknown” values: NULL ........................................................ 71 Connecting conditions with logical operators .......................... 77 CHAPTER 3 Using Aggregates, Grouping, and Sorting.................................. 79 Using aggregate functions ............................................................. 79 Aggregate functions and datatypes......................................... 81 count vs. count(*) .................................................................... 82 Using aggregate functions with distinct ................................... 83 Null values and the aggregate functions ................................. 84 Organizing query results into groups: the group by clause ............ 85Contents Transact-SQL User’s Guide v group by syntax ....................................................................... 86 Referencing other columns in queries using group by ............ 88 Expressions and group by ....................................................... 91 Nesting aggregates with group by........................................... 92 Null values and group by......................................................... 93 where clause and group by ..................................................... 94 group by and all....................................................................... 95 Using aggregates without group by......................................... 96 Selecting groups of data: the having clause .................................. 97 How the having, group by, and where clauses interact........... 99 Using having without group by .............................................. 101 Sorting query results: the order by clause.................................... 103 order by and group by ........................................................... 104 order by and group by used with select distinct .................... 105 Summarizing groups of data: the compute clause ....................... 106 Row aggregates and compute .............................................. 109 Specifying more than one column after compute .................. 110 Using more than one compute clause................................... 111 Applying an aggregate to more than one column.................. 111 Using different aggregates in the same compute clause ...... 112 Grand values: compute without by ........................................ 113 Combining queries: the union operator ........................................ 114 Guidelines for union queries.................................................. 116 Using union with other Transact-SQL commands................. 118 CHAPTER 4 Subqueries: Using Queries Within Other Queries ................... 121 How subqueries work................................................................... 121 Subquery syntax.................................................................... 122 Subquery restrictions............................................................. 123 Example of using a subquery ................................................ 124 Qualifying column names ...................................................... 125 Subqueries with correlation names ....................................... 125 Multiple levels of nesting ....................................................... 127 Subqueries in update, delete, and insert statements ............ 128 Subqueries in conditional statements.................................... 129 Using subqueries instead of expressions.............................. 129 Types of subqueries..................................................................... 130 Expression subqueries .......................................................... 131 Quantified predicate subqueries............................................ 134 Subqueries used with in ........................................................ 140 Subqueries used with not in .................................................. 142 Subqueries using not in with NULL ....................................... 142 Subqueries used with exists .................................................. 143 Subqueries used with not exists............................................ 146Contents vi Adaptive Server Enterprise Finding intersection and difference with exists...................... 146 Subqueries using SQL derived tables ................................... 147 Using correlated subqueries ........................................................ 148 Correlated subqueries containing Transact-SQL outer joins. 149 Correlated subqueries with correlation names ...................... 150 Correlated subqueries with comparison operators................ 151 Correlated subqueries in a having clause ............................. 152 CHAPTER 5 SQL Derived Tables..................................................................... 155 Differences from abstract plan derived tables.............................. 155 How SQL derived tables work ...................................................... 155 Advantages of SQL derived tables............................................... 156 SQL derived tables and optimization..................................... 157 SQL derived table syntax ............................................................. 157 Derived column lists .............................................................. 159 Correlated SQL derived tables .............................................. 159 Using SQL derived tables ............................................................ 160 Nesting .................................................................................. 160 Subqueries using SQL derived tables ................................... 160 Unions ................................................................................... 161 Unions in subqueries............................................................. 161 Renaming columns with SQL derived tables......................... 161 Constant expressions............................................................ 162 Aggregate functions .............................................................. 163 Joins with SQL derived tables ............................................... 163 Creating a table from a SQL derived table ............................ 164 Correlated attributes.............................................................. 165 CHAPTER 6 Joins: Retrieving Data from Several Tables.............................. 167 How joins work ............................................................................. 168 Join syntax ............................................................................ 168 Joins and the relational model............................................... 169 How joins are structured .............................................................. 169 The from clause..................................................................... 171 The where clause .................................................................. 172 How joins are processed.............................................................. 174 Equijoins and natural joins ........................................................... 175 Joins with additional conditions .................................................... 176 Joins not based on equality.......................................................... 177 Self-joins and correlation names .................................................. 178 The not-equal join ........................................................................ 179 Not-equal joins and subqueries............................................. 181 Joining more than two tables ....................................................... 182Contents Transact-SQL User’s Guide vii Outer joins.................................................................................... 184 Inner and outer tables ........................................................... 184 Outer join restrictions ............................................................ 185 Views used with outer joins ................................................... 185 ANSI Inner and outer joins .................................................... 186 ANSI outer joins .................................................................... 192 Transact-SQL outer joins ...................................................... 204 How null values affect joins.......................................................... 207 Determining which table columns to join...................................... 208 CHAPTER 7 Using and Creating Datatypes................................................... 211 How Transact-SQL datatypes work ............................................. 211 Using system-supplied datatypes ................................................ 212 Exact numeric types: integers ............................................... 214 Exact numeric types: decimal numbers................................. 214 Approximate numeric datatypes............................................ 215 Money datatypes ................................................................... 215 Date and time datatypes ....................................................... 215 Character datatypes .............................................................. 216 Binary datatypes.................................................................... 221 The bit datatype..................................................................... 222 The timestamp datatype........................................................ 223 The sysname datatype .......................................................... 223 Converting between datatypes..................................................... 223 Mixed-mode arithmetic and datatype hierarchy ........................... 224 Working with money datatypes ............................................. 225 Determining precision and scale ........................................... 226 Creating user-defined datatypes .................................................. 226 Specifying length, precision, and scale ................................. 227 Specifying null type ............................................................... 228 Associating rules and defaults with user-defined datatypes.. 228 Creating a user-defined datatype with the IDENTITY property 228 Creating IDENTITY columns from other user-defined datatypes . 229 Dropping a user-defined datatype ......................................... 229 Getting information about datatypes ............................................ 229 CHAPTER 8 Creating Databases and Tables................................................. 231 What are databases and tables? ................................................. 231 Enforcing data integrity in databases .................................... 232 Permissions within databases ............................................... 233 Using and creating databases...................................................... 234 Choosing a database: use..................................................... 235Contents viii Adaptive Server Enterprise Creating a user database: create database .......................... 236 Altering the sizes of databases .................................................... 239 Dropping databases ..................................................................... 240 Creating tables ............................................................................. 240 Maximum number of columns per table ................................ 241 Example of creating a table................................................... 241 Choosing table names........................................................... 242 create table syntax ................................................................ 242 Allowing null values ............................................................... 244 Using IDENTITY columns ..................................................... 247 Using temporary tables ......................................................... 250 Creating tables in different databases................................... 254 Managing identity gaps in tables .................................................. 254 Parameters for controlling identity gaps ................................ 255 Comparison of identity burning set factor and identity_gap .. 256 Setting the table-specific identity gap.................................... 258 Changing the table-specific identity gap................................ 258 Displaying table-specific identity gap information.................. 259 Gaps due to insertions, deletions, identity grab size, and rollbacks 261 If table inserts reach the IDENTITY column’s maximum value 262 Defining integrity constraints for tables ........................................ 263 Specifying table-level or column-level constraints................. 264 Creating error messages for constraints ............................... 265 After creating a check constraint ........................................... 266 Specifying default column values .......................................... 266 Specifying unique and primary key constraints ..................... 267 Specifying referential integrity constraints............................. 268 Specifying check constraints ................................................. 271 Designing applications that use referential integrity .............. 272 How to design and create a table................................................. 274 Make a design sketch............................................................ 275 Create the user-defined datatypes ........................................ 276 Choose the columns that accept null values ......................... 276 Define the table ..................................................................... 276 Creating new tables from query results: select into ..................... 277 Checking for errors................................................................ 280 Using select into with IDENTITY columns............................. 280 Altering existing tables ................................................................. 283 Objects using select * do not list changes to table ................ 284 Using alter table on remote tables......................................... 285 Adding columns..................................................................... 285 Dropping columns ................................................................. 287 Modifying columns................................................................. 289Contents Transact-SQL User’s Guide ix Adding, dropping, and modifying IDENTITY columns ........... 293 Data copying ......................................................................... 295 Modifying locking schemes and table schema ...................... 297 Altering columns with user defined datatypes ....................... 297 Errors and warnings from alter table ..................................... 298 Renaming tables and other objects....................................... 301 Dropping tables ............................................................................ 302 Assigning permissions to users.................................................... 303 Getting information about databases and tables.......................... 305 Getting help on databases .................................................... 305 Getting help on database objects.......................................... 306 CHAPTER 9 Adding, Changing, and Deleting Data....................................... 313 Introduction .................................................................................. 313 Permissions........................................................................... 314 Referential integrity ............................................................... 314 Transactions.......................................................................... 315 Using the sample databases ................................................. 315 Datatype entry rules ..................................................................... 316 char, nchar, unichar, univarchar, varchar, nvarchar, and text 316 date and time data types ....................................................... 317 binary, varbinary, and image ................................................. 322 money and smallmoney ........................................................ 322 float, real, and double precision ............................................ 323 decimal and numeric ............................................................. 323 int, smallint, and tinyint .......................................................... 324 timestamp.............................................................................. 324 Adding new data .......................................................................... 324 insert syntax .......................................................................... 325 Adding new rows with values ................................................ 325 Inserting data into specific columns ...................................... 326 Adding new rows with select ................................................. 334 Changing existing data................................................................. 337 update syntax ........................................................................ 338 Using the set clause with update........................................... 339 Using the where clause with update...................................... 340 Using the from clause with update ........................................ 341 Updates with joins ................................................................. 341 Updating IDENTITY columns ................................................ 342 Changing text and image data ..................................................... 342 Deleting data ................................................................................ 343 Using the from clause with delete ......................................... 344 Deleting from IDENTITY columns ......................................... 345 Deleting all rows from a table....................................................... 346Contents x Adaptive Server Enterprise truncate table syntax ............................................................. 346 CHAPTER 10 Views: Limiting Access to Data.................................................. 347 How views work ........................................................................... 347 Advantages of views ............................................................. 348 View examples ...................................................................... 350 Creating views.............................................................................. 352 create view syntax................................................................. 352 Using the select statement with create view ......................... 354 After creating a view.............................................................. 358 Validating a view’s selection criteria using with check option 359 Retrieving data through views ...................................................... 360 View resolution ...................................................................... 361 Redefining views ................................................................... 362 Renaming views .................................................................... 363 Altering or dropping underlying objects ................................. 363 Modifying data through views....................................................... 364 Restrictions on updating views.............................................. 365 Dropping views............................................................................. 368 Using views as security mechanisms........................................... 369 Getting information about views ................................................... 369 Getting help on views with sp_help ....................................... 370 Using sp_helptext to display view information....................... 371 Using sp_depends to list dependent objects......................... 371 Listing all views in a database............................................... 372 CHAPTER 11 Using the Built-In Functions in Queries .................................... 373 System functions that return database information...................... 373 Examples of using system functions ..................................... 377 String functions used for character strings or expressions .......... 379 Examples of using string functions........................................ 382 Concatenation ....................................................................... 387 Nested string functions.......................................................... 388 Text functions used for text and image data ................................ 389 Readtext................................................................................ 390 Examples of using text functions........................................... 391 Aggregate functions ..................................................................... 392 Mathematical functions ................................................................ 393 Examples of using mathematical functions ........................... 395 Date functions .............................................................................. 396 Get current date: getdate ...................................................... 399 Find date parts as numbers or names................................... 400 Calculate intervals or increment dates .................................. 401Contents Transact-SQL User’s Guide xi Add date interval: dateadd .................................................... 401 Datatype conversion functions ..................................................... 402 Using the general purpose conversion function: convert ...... 403 Conversion rules ................................................................... 404 Converting binary-like data.................................................... 406 Conversion errors.................................................................. 408 Security functions......................................................................... 412 CHAPTER 12 Creating Indexes on Tables ....................................................... 415 How indexes work ........................................................................ 415 Comparing the two ways to create indexes........................... 416 Guidelines for Using Indexes ................................................ 417 Creating indexes .......................................................................... 418 create index syntax ............................................................... 419 Indexing more than one column: Composite indexes ........... 419 Using the unique option......................................................... 420 Including IDENTITY columns in nonunique indexes ............. 420 Ascending and descending index-column values ................. 421 Using fillfactor, max_rows_per_page, and reservepagegap . 422 Using clustered or nonclustered indexes ..................................... 423 Creating clustered indexes on segments .............................. 425 Creating clustered indexes on partitioned tables .................. 425 Specifying index options .............................................................. 425 Using the ignore_dup_key option.......................................... 426 Using the ignore_dup_row and allow_dup_row options........ 426 Using the sorted_data option ................................................ 427 Using the on segment_name option...................................... 428 Dropping indexes ......................................................................... 428 Determining what indexes exist on a table................................... 429 Updating statistics about indexes................................................. 431 Updating partition statistics ................................................... 432 CHAPTER 13 Defining Defaults and Rules for Data........................................ 433 How defaults and rules work ........................................................ 433 Creating defaults .......................................................................... 434 create default syntax ............................................................. 435 Binding defaults..................................................................... 436 Unbinding defaults................................................................. 438 How defaults affect NULL values .......................................... 439 After creating a default .......................................................... 439 Dropping defaults ......................................................................... 440 Creating rules............................................................................... 440 create rule syntax .................................................................. 440Contents xii Adaptive Server Enterprise Binding rules.......................................................................... 442 Rules and NULL values......................................................... 444 After defining a rule ............................................................... 444 Unbinding rules ..................................................................... 444 Dropping rules.............................................................................. 445 Getting information about defaults and rules ............................... 445 CHAPTER 14 Using Batches and Control-of-Flow Language......................... 447 Introduction .................................................................................. 447 Rules associated with batches ..................................................... 448 Examples of using batches ................................................... 450 Batches submitted as files..................................................... 452 Using control-of-flow language..................................................... 453 if...else ................................................................................... 454 case expression .................................................................... 456 begin...end............................................................................. 466 while and break...continue..................................................... 466 declare and local variables.................................................... 469 goto ....................................................................................... 469 return ..................................................................................... 470 print ....................................................................................... 470 raiserror ................................................................................. 472 Creating messages for print and raiserror ............................. 473 waitfor.................................................................................... 474 Comments ............................................................................. 476 Local variables ............................................................................. 478 Declaring local variables ....................................................... 478 Local variables and select statements .................................. 478 Local variables and update statements................................. 480 Local variables and subqueries............................................. 480 Local variables and while loops and if…else blocks ............. 481 Variables and null values ...................................................... 481 Global variables ........................................................................... 483 Transactions and global variables......................................... 483 Global variables affected by set options................................ 485 Language and character set information in global variables . 487 Global variables for monitoring system activity ..................... 487 Server information stored in global variables ........................ 488 Global variables and text and image data ............................. 490 CHAPTER 15 Using Stored Procedures............................................................ 491 How stored procedures work ....................................................... 491 Examples of creating and using stored procedures .............. 492Contents Transact-SQL User’s Guide xiii Stored procedures and permissions...................................... 494 Stored Procedures and Performance.................................... 495 Creating and executing stored procedures .................................. 495 Parameters............................................................................ 496 Default parameters................................................................ 498 Using more than one parameter............................................ 501 Procedure groups.................................................................. 503 Using with recompile in create procedure ............................. 503 Using with recompile in execute............................................ 504 Nesting procedures within procedures .................................. 504 Using temporary tables in stored procedures........................ 505 Setting options in stored procedures..................................... 506 After creating a stored procedure.......................................... 507 Executing stored procedures................................................. 508 Returning information from stored procedures............................. 509 Return status ......................................................................... 510 Checking roles in procedures ................................................ 512 Return parameters ................................................................ 513 Restrictions associated with stored procedures........................... 517 Qualifying names inside procedures ..................................... 518 Renaming stored procedures....................................................... 519 Renaming objects referenced by procedures........................ 519 Using stored procedures as security mechanisms....................... 519 Dropping stored procedures......................................................... 520 System procedures ...................................................................... 520 Executing system procedures ............................................... 521 Permissions on system procedures ...................................... 521 Types of system procedures ................................................. 521 Other Sybase-supplied procedures....................................... 527 Getting information about stored procedures............................... 528 Getting a report with sp_help ................................................ 529 Viewing the source text of a procedure with sp_helptext ...... 529 Identifying dependent objects with sp_depends.................... 530 Identifying permissions with sp_helprotect............................ 530 CHAPTER 16 Using Extended Stored Procedures.......................................... 533 Overview ...................................................................................... 533 XP Server .............................................................................. 534 Dynamic Link Library Support ............................................... 535 Open Server API ................................................................... 535 Example of creating and using ESPs .................................... 536 ESPs and Permissions .......................................................... 537 ESPs and Performance......................................................... 538 Creating functions for ESPs ......................................................... 539Contents xiv Adaptive Server Enterprise Files for ESP Development ................................................... 539 Open Server data structures ................................................. 539 Open Server return codes ..................................................... 540 Outline of a simple ESP function........................................... 540 ESP function example ........................................................... 541 Building the DLL .................................................................... 547 Registering ESPs ......................................................................... 550 Using create procedure ......................................................... 550 Using sp_addextendedproc................................................... 551 Removing ESPs ........................................................................... 552 Renaming ESPs .................................................................... 552 Executing ESPs ........................................................................... 552 System ESPs ............................................................................... 554 Getting information about ESPs ................................................... 554 ESP exceptions and messages ................................................... 555 Starting XP Server manually ........................................................ 556 CHAPTER 17 Triggers: Enforcing Referential Integrity................................... 557 How triggers work ........................................................................ 557 Using triggers vs. integrity constraints................................... 559 Creating triggers........................................................................... 559 create trigger syntax.............................................................. 560 Using triggers to maintain referential integrity.............................. 561 Testing data modifications against the trigger test tables ..... 563 Insert trigger example............................................................ 564 Delete trigger examples ........................................................ 565 Update trigger examples ....................................................... 567 Multirow considerations................................................................ 573 Insert trigger example using multiple rows ............................ 573 Delete trigger example using multiple rows........................... 574 Update trigger example using multiple rows ......................... 574 Conditional insert trigger example using multiple rows ......... 575 Rolling back triggers..................................................................... 577 Nesting triggers ............................................................................ 579 Trigger self-recursion ............................................................ 580 Rules associated with triggers ..................................................... 581 Triggers and permissions ...................................................... 582 Trigger restrictions................................................................. 582 Implicit and explicit null values .............................................. 583 Triggers and performance ..................................................... 584 set commands in triggers ...................................................... 584 Renaming and triggers .......................................................... 585 Trigger tips ............................................................................ 585 Disabling triggers ......................................................................... 585Contents Transact-SQL User’s Guide xv Dropping triggers.......................................................................... 586 Getting information about triggers................................................ 587 sp_help.................................................................................. 587 sp_helptext ............................................................................ 588 sp_depends........................................................................... 589 CHAPTER 18 Cursors: Accessing Data Row by Row..................................... 591 How cursors work......................................................................... 591 How Adaptive Server processes cursors .............................. 592 Declaring cursors ......................................................................... 596 declare cursor syntax ............................................................ 596 Types of cursors.................................................................... 597 Cursor scope ......................................................................... 598 Cursor scans and the cursor result set.................................. 600 Making cursors updatable ..................................................... 601 Determining which columns can be updated......................... 602 Opening cursors........................................................................... 604 Fetching data rows using cursors ................................................ 604 fetch syntax ........................................................................... 604 Checking the cursor status .................................................... 605 Getting multiple rows with each fetch.................................... 606 Checking the number of rows fetched................................... 607 Updating and deleting rows using cursors ................................... 608 Updating cursor result set rows............................................. 608 Deleting cursor result set rows .............................................. 609 Closing and deallocating cursors ................................................. 610 An example using a cursor........................................................... 611 Using cursors in stored procedures ............................................. 613 Cursors and locking ..................................................................... 615 Cursor locking options ........................................................... 616 Getting information about cursors ................................................ 617 Using browse mode instead of cursors ........................................ 618 Browsing a table.................................................................... 618 Browse-mode restrictions ...................................................... 619 Timestamping a new table for browsing................................ 619 Timestamping an existing table............................................. 619 Comparing timestamp values ................................................ 620 Join cursor processing and data modifications ............................ 620 Updates and deletes that can affect the cursor position ....... 620 Cursor positioning after a delete or update command without joins 621 Effects of updates and deletes on join cursors...................... 621 Effects of join column buffering on join cursors..................... 623 Recommendations ................................................................ 626Contents xvi Adaptive Server Enterprise CHAPTER 19 Transactions: Maintaining Data Consistency and Recovery .. 629 How transactions work ................................................................. 629 Transactions and consistency ............................................... 632 Transactions and recovery .................................................... 632 Using transactions........................................................................ 633 Allowing data definition commands in transactions............... 633 System procedures that are not allowed in transactions....... 634 Beginning and committing transactions................................. 635 Rolling back and saving transactions .................................... 635 Checking the state of transactions ........................................ 637 Nested transactions............................................................... 639 Example of a transaction....................................................... 640 Selecting the transaction mode and isolation level ...................... 641 Choosing a transaction mode................................................ 642 Choosing an isolation level.................................................... 644 Compliance with SQL standards ........................................... 652 Using the lock table command to improve performance ....... 652 Using the wait/nowait options of the lock table command..... 653 Using transactions in stored procedures and triggers.................. 654 Errors and transaction rollbacks............................................ 656 Transaction modes and stored procedures........................... 660 Using cursors in transactions ....................................................... 662 Issues to consider when using transactions................................. 663 Backup and recovery of transactions ........................................... 664 CHAPTER 20 Locking Commands and Options .............................................. 667 Setting a time limit on waiting for locks ........................................ 667 wait/nowait option of the lock table command....................... 668 Setting a session-level lock-wait limit.................................... 669 Setting a server-wide lock-wait limit ...................................... 669 Information on the number of lock-wait timeouts................... 670 Readpast locking for queue processing ....................................... 671 Readpast syntax.................................................................... 671 Incompatible locks during readpast queries .......................... 671 Allpages-locked tables and readpast queries........................ 672 Effects of isolation levels select queries with readpast ......... 672 Data modification commands with readpast and isolation levels . 673 text and image columns and readpast .................................. 674 Readpast-locking examples .................................................. 674 A P P E N D I X A The pubs2 Database.................................................................... 677 Tables in the pubs2 database ...................................................... 677Contents Transact-SQL User’s Guide xvii publishers table ..................................................................... 677 authors table.......................................................................... 678 titles table .............................................................................. 680 titleauthor table...................................................................... 687 salesdetail table..................................................................... 689 sales table ............................................................................. 694 stores table............................................................................ 695 roysched table ....................................................................... 696 discounts table ...................................................................... 700 blurbs table............................................................................ 701 au_pix table ........................................................................... 702 Diagram of the pubs2 database ................................................... 705 A P P E N D I X B The pubs3 Database ................................................................... 707 Tables in the pubs3 database ...................................................... 707 publishers table ..................................................................... 707 authors table.......................................................................... 708 titles table .............................................................................. 710 titleauthor table...................................................................... 717 salesdetail table..................................................................... 719 sales table ............................................................................. 725 stores table............................................................................ 726 store_employees table .......................................................... 727 roysched table ....................................................................... 732 discounts table ...................................................................... 736 blurbs table............................................................................ 737 Diagram of the pubs3 database ................................................... 739 Index ........................................................................................................................................... 741Contents xviii Adaptive Server EnterpriseTransact-SQL User’s Guide xix About This Book This manual, the Transact-SQL User’s Guide, documents TransactSQL®, an enhanced version of the SQL relational database language. The Transact-SQL User’s Guide is intended for both beginners and those who have experience with other implementations of SQL. Audience Users of the Sybase® Adaptive Server™ Enterprise database management systems who are unfamiliar with SQL can consider this guide as a textbook and start at the beginning. Novice SQL users should concentrate on the first part of this book. The second part describes advanced topics. This manual is useful both as a review, for those acquainted with other versions of SQL, and as a guide to Transact-SQL enhancements. SQL experts should study the capabilities and features that Transact-SQL has added to standard SQL, especially the material on stored procedures. How to use this book This book is a complete guide to Transact-SQL. It contains an introductory chapter, which gives an overview of SQL. The remaining chapters are divided into two subjects: Basic Concepts and Advanced Topics. Chapter 1, “SQL Building Blocks,” describes the naming conventions used by SQL and the enhancements (also known as extensions) added by Transact-SQL. It also includes a description of how to get started with Transact-SQL using the isql utility. Sybase recommends that all users read this chapter. Chapters 2–9 introduce you to the basic functionality of SQL. Users new to SQL should become familiar with the concepts described in these chapters before moving on to Chapters 10–18. Experienced users of SQL may want to skim through these chapters to learn about the Transact-SQL extensions introduced there and to review the material. Chapters 10–18 describe Transact-SQL in more detail. Most of the Transact-SQL extensions are described here. Users familiar with SQL, but not Transact-SQL, should concentrate on these chapters.xx Adaptive Server Enterprise The examples in this guide are based on the pubs2 and, where noted, pubs3 sample databases. For best use of the Transact-SQL User’s Guide, new users should work through the examples. Ask your System Administrator how to get a clean copy of pubs2 and pubs3. For a complete description of these databases, see Appendix A, “The pubs2 Database,” and Appendix B, “The pubs3 Database.” You can use Transact-SQL with the Adaptive Server standalone program isql. The isql program is a utility program called directly from the operating system. Related documents The Sybase ® Adaptive Server ® Enterprise documentation set consists of the following: • The release bulletin for your platform – contains last-minute information that was too late to be included in the books. A more recent version of the release bulletin may be available on the World Wide Web. To check for critical product or document information that was added after the release of the product CD, use the Sybase Technical Library. • The Installation Guide for your platform – describes installation, upgrade, and configuration procedures for all Adaptive Server and related Sybase products. • What’s New in Adaptive Server Enterprise? – describes the new features in Adaptive Server version 12.5.1, the system changes added to support those features, and the changes that may affect your existing applications. • ASE Replicator User’s Guide – describes how to use the ASE Replicator feature of Adaptive Server to implement basic replication from a primary server to one or more remote Adaptive Servers. • Component Integration Services User’s Guide – explains how to use the Adaptive Server Component Integration Services feature to connect remote Sybase and non-Sybase databases. • Configuring Adaptive Server Enterprise for your platform – provides instructions for performing specific configuration tasks for Adaptive Server. • EJB Server User’s Guide – explains how to use EJB Server to deploy and execute Enterprise JavaBeans in Adaptive Server. • Error Messages and Troubleshooting Guide – explains how to resolve frequently occurring error messages and describes solutions to system problems frequently encountered by users. About This Book Transact-SQL User’s Guide xxi • Full-Text Search Specialty Data Store User’s Guide – describes how to use the Full-Text Search feature with Verity to search Adaptive Server Enterprise data. • Glossary – defines technical terms used in the Adaptive Server documentation. • Historical Server User’s Guide – describes how to use Historical Server to obtain performance information for SQL Server ® and Adaptive Server. • Java in Adaptive Server Enterprise – describes how to install and use Java classes as data types, functions, and stored procedures in the Adaptive Server database. • Job Scheduler User’s Guide – provides instructions on how to install and configure, and create and schedule jobs on a local or remote Adaptive Server using the command line or a graphical user interface (GUI). • Monitor Client Library Programmer’s Guide – describes how to write Monitor Client Library applications that access Adaptive Server performance data. • Monitor Server User’s Guide – describes how to use Monitor Server to obtain performance statistics from SQL Server and Adaptive Server. • Performance and Tuning Guide – is a series of four books that explains how to tune Adaptive Server for maximum performance: • Basics – the basics for understanding and investigating performance questions in Adaptive Server. • Locking – describes how the various locking schemas can be used for improving performance in Adaptive Server. • Optimizer and Abstract Plans – describes how the optimizer processes queries and how abstract plans can be used to change some of the optimizer plans. • Monitoring and Analyzing – explains how statistics are obtained and used for monitoring and optimizing performance. • Quick Reference Guide – provides a comprehensive listing of the names and syntax for commands, functions, system procedures, extended system procedures, datatypes, and utilities in a pocket-sized book. • Reference Manual – is a series of four books that contains the following detailed Transact-SQL ® information:xxii Adaptive Server Enterprise • Building Blocks – Transact-SQL datatypes, functions, global variables, expressions, identifiers and wildcards, and reserved words. • Commands – Transact-SQL commands. • Procedures – Transact-SQL system procedures, catalog stored procedures, system extended stored procedures, and dbcc stored procedures. • Tables – Transact-SQL system tables and dbcc tables. • System Administration Guide – provides in-depth information about administering servers and databases. This manual includes instructions and guidelines for managing physical resources, security, user and system databases, and specifying character conversion, international language, and sort order settings. • System Tables Diagram – illustrates system tables and their entity relationships in a poster format. Available only in print version. • Transact-SQL User’s Guide – documents Transact-SQL, Sybase’s enhanced version of the relational database language. This manual serves as a textbook for beginning users of the database management system. This manual also contains descriptions of the pubs2 and pubs3 sample databases. • Using Adaptive Server Distributed Transaction Management Features – explains how to configure, use, and troubleshoot Adaptive Server DTM features in distributed transaction processing environments. • Using Sybase Failover in a High Availability System – provides instructions for using Sybase’s Failover to configure an Adaptive Server as a companion server in a high availability system. • Utility Guide – documents the Adaptive Server utility programs, such as isql and bcp, which are executed at the operating system level. • Web Services User’s Guide – explains how to configure, use, and troubleshoot Web Services for Adaptive Server. • XA Interface Integration Guide for CICS, Encina, and TUXEDO – provides instructions for using the Sybase DTM XA interface with X/Open XA transaction managers. • XML Services in Adaptive Server Enterprise – describes the Sybase native XML processor and the Sybase Java-based XML support, introduces XML in the database, and documents the query and mapping functions that comprise XML Services. About This Book Transact-SQL User’s Guide xxiii Other sources of information Use the Sybase Getting Started CD, the Sybase Technical Library CD and the Technical Library Product Manuals Web site to learn more about your product: • The Getting Started CD contains release bulletins and installation guides in PDF format, and may also contain other documents or updated information not included on the Technical Library CD. It is included with your software. To read or print documents on the Getting Started CD you need Adobe Acrobat Reader (downloadable at no charge from the Adobe Web site, using a link provided on the CD). • The Technical Library CD contains product manuals and is included with your software. The DynaText reader (included on the Technical Library CD) allows you to access technical information about your product in an easy-to-use format. Refer to the Technical Library Installation Guide in your documentation package for instructions on installing and starting the Technical Library. • The Technical Library Product Manuals Web site is an HTML version of the Technical Library CD that you can access using a standard Web browser. In addition to product manuals, you will find links to EBFs/Updates, Technical Documents, Case Management, Solved Cases, newsgroups, and the Sybase Developer Network. To access the Technical Library Product Manuals Web site, go to Product Manuals at http://www.sybase.com/support/manuals/. Sybase certifications on the Web Technical documentation at the Sybase Web site is updated frequently. ? Finding the latest information on product certifications 1 Point your Web browser to Technical Documents at http://www.sybase.com/support/techdocs/. 2 Select Products from the navigation bar on the left. 3 Select a product name from the product list and click Go. 4 Select the Certification Report filter, specify a time frame, and click Go. 5 Click a Certification Report title to display the report. ? Creating a personalized view of the Sybase Web site (including support pages) Set up a MySybase profile. MySybase is a free service that allows you to create a personalized view of Sybase Web pages.xxiv Adaptive Server Enterprise 1 Point your Web browser to Technical Documents at http://www.sybase.com/support/techdocs/. 2 Click MySybase and create a MySybase profile. Sybase EBFs and software updates ? Finding the latest information on EBFs and software updates 1 Point your Web browser to the Sybase Support Page at http://www.sybase.com/support. 2 Select EBFs/Updates. Enter user name and password information, if prompted (for existing Web accounts) or create a new account (a free service). 3 Select a product. 4 Specify a time frame and click Go. 5 Click the Info icon to display the EBF/Update report, or click the product description to download the software. Conventions The following sections describe conventions used in this manual. SQL is a free-form language. There are no rules about the number of words you can put on a line or where you must break a line. However, for readability, all examples and most syntax statements in this manual are formatted so that each clause of a statement begins on a new line. Clauses that have more than one part extend to additional lines, which are indented. Complex commands are formatted using modified Backus Naur Form (BNF) notation. Table 1 shows the conventions for syntax statements that appear in this manual: Table 1: Font and syntax conventions for this manual Element Example Command names,procedure names, utility names, and other keywords display in sans serif font. select sp_configure Database names and datatypes are in sans serif font. master database Book names, file names, variables, and path names are in italics. System Administration Guide sql.ini file column_name $SYBASE/ASE directory Variables—or words that stand for values that you fill in—when they are part of a query or statement, are in italics in Courier font. select column_name from table_name where search_conditions Type parentheses as part of the command. compute row_aggregate (column_name) About This Book Transact-SQL User’s Guide xxv • Syntax statements (displaying the syntax and all options for a command) appear as follows: sp_dropdevice [device_name] For a command with more options: select column_name from table_name where search_conditions In syntax statements, keywords (commands) are in normal font and identifiers are in lowercase. Italic font shows user-supplied words. • Examples showing the use of Transact-SQL commands are printed like this: select * from publishers • Examples of output from the computer appear as follows: pub_id pub_name city state ------- --------------------- ----------- ----- 0736 New Age Books Boston MA 0877 Binnet & Hardley Washington DC Double colon, equals sign indicates that the syntax is written in BNF notation. Do not type this symbol. Indicates “is defined as”. ::= Curly braces mean that you must choose at least one of the enclosed options. Do not type the braces. {cash | check | credit} Brackets mean that to choose one or more of the enclosed options is optional. Do not type the brackets. [cash | check | credit] The comma means you may choose as many of the options shown as you want. Separate your choices with commas as part of the command. cash, check, credit The pipe or vertical bar( | ) means you may select only one of the options shown. cash | check | credit An ellipsis (...) means that you can repeat the last unit as many times as you like. buy thing = price [cash | check | credit] [, thing = price [cash | check | credit]]... You must buy at least one thing and give its price. You may choose a method of payment: one of the items enclosed in square brackets. You may also choose to buy additional things: as many of them as you like. For each thing you buy, give its name, its price, and (optionally) a method of payment. Element Examplexxvi Adaptive Server Enterprise 1389 Algodata Infosystems Berkeley CA (3 rows affected) In this manual, most of the examples are in lowercase. However, you can disregard case when typing Transact-SQL keywords. For example, SELECT, Select, and select are the same. Adaptive Server’s sensitivity to the case of database objects, such as table names, depends on the sort order installed on Adaptive Server. You can change case sensitivity for single-byte character sets by reconfiguring the Adaptive Server sort order. For more information, see the System Administration Guide. If you need help Each Sybase installation that has purchased a support contract has one or more designated people who are authorized to contact Sybase Technical Support. If you cannot resolve a problem using the manuals or online help, please have the designated person contact Sybase Technical Support or the Sybase subsidiary in your area.Transact-SQL User’s Guide 1 C H A P T E R 1 SQL Building Blocks This chapter discusses: SQL in Adaptive Server SQL (Structured Query Language) is a high-level language used in relational database systems. Originally developed by IBM’s San Jose Research Laboratory in the late 1970s, SQL has been adopted by, and adapted for, many relational database management systems. It has been approved as the official relational query language standard by the American National Standards Institute (ANSI) and the International Organization for Standardization (ISO). Transact-SQL, Sybase’s extension of SQL, is compatible with IBM SQL and most other commercial implementations of SQL. It provides important extra capabilities and functions, such as summary calculations, stored procedures (predefined SQL statements), and error handling. Topic Page SQL in Adaptive Server 1 Naming conventions 6 Expressions in Adaptive Server 13 Transact-SQL extensions 20 Compliance to ANSI standards 26 Adaptive Server login accounts 31 How to use Transact-SQL with the isql utility 35 Using the pubs2 and pubs3 sample databases 37SQL in Adaptive Server 2 Adaptive Server Enterprise SQL includes commands not only for querying (retrieving data from) a database, but also for creating new databases and database objects, adding new data, modifying existing data, and other functions. Note If Java is enabled on your Adaptive Server, you can install and use Java classes in the database. You can invoke Java operations and store Java classes using standard Transact-SQL commands. Refer to Java in Adaptive Server Enterprise for a complete description of this feature. Queries, data modification, and commands In SQL, a query requests data using the select command. For example, this query asks for a listing of authors who live in the state of California: select au_lname, city, state from authors where state = "CA" Data modification refers to the addition, deletion, or change of data using the insert, delete, or update commands. For example: insert into authors (au_lname, au_fname, au_id) values ("Smith", "Gabriella", "999-03-2346") Other SQL commands, such as dropping tables or adding users, perform administrative operations. For example: drop table authors Each command or SQL statement begins with a keyword, such as insert, that names the basic operation performed. Many SQL commands also have one or more keyword phrases, or clauses, that tailor the command to meet a particular need. When you run a query, Transact-SQL displays the results. If no data meets the criteria specified in the query, the user gets a message to that effect. Data modification statements and administrative statements do not retrieve data, and therefore, do not display results. Transact-SQL provides a message to let the user know whether the data modification or other command has been performed. CHAPTER 1 SQL Building Blocks Transact-SQL User’s Guide 3 Tables, columns, and rows In relational database management systems, users access and modify data stored in tables. SQL is specifically designed for the relational model of database management. Each row, or record, in a table describes one occurrence of a piece of data—a person, a company, a sale, or some other thing. Each column, or field, describes one characteristic of the data—a person’s name or address, a company’s name or president, quantity of items sold. A relational database is made up of a set of tables that can be related to each other. Figure 1-1: Multiple tables in a database The relational operations The basic query operations in a relational system are selection (also called restriction), projection, and join. These can all be combined in the SQL select command. A selection is a subset of the rows in a table. You specify the limiting conditions in the select query. For example, you might want to look only at the rows for all authors who live in California. select * from authors where state = "CA" A projection is a subset of the columns in a table. For example, this query displays only the name and city of all authors, omitting the street address, the phone number, and other information. select au_fname, au_lname, city from authorsSQL in Adaptive Server 4 Adaptive Server Enterprise A join links the rows in two or more tables by comparing the values in specified fields. For example, suppose you have one table containing information about authors, including the columns au_id (author identification number) and au_lname (author’s last name). A second table contains title information about books, including a column that gives the ID number of the book’s author (au_id). You might join the authors table and the titles table, testing for equality of the values in the au_id columns of each table. Whenever there is a match, a new row—containing columns from both tables—is created and displayed as part of the result of the join. Joins are often combined with projections and selections so that only selected columns of selected matching rows display. select * from authors, publishers where authors.city = publishers.city Compiled objects Adaptive Server uses compiled objects to contain vital information about each database and to help you access and manipulate data. A compiled object is any object that requires entries in the sysprocedures table, including: • Check constraints • Defaults • Rules • Stored procedures • Extended stored procedures • Triggers • Views Compiled objects are created from source text, which are SQL statements that describe and define the compiled object. When a compiled object is created, Adaptive Server: 1 Parses the source text, catching any syntactic errors, to generate a parsed tree. 2 Normalizes the parsed tree to create a normalized tree, which represents the user statements in a binary tree format. This is the compiled object. 3 Stores the compiled object in the sysprocedures table.CHAPTER 1 SQL Building Blocks Transact-SQL User’s Guide 5 4 Stores the source text in the syscomments table. Note If you are upgrading from Adaptive Server version 11.5 or earlier, and you have deleted source text from syscomments, you must restore the deleted portions before you upgrade. To do so, follow the process in the installation documentation for your platform. Saving source text In Adaptive Server version 11.5 and in SQL Server® versions prior to that release, the source text was saved in syscomments so it could be returned to a user who executed sp_helptext. Because this was the only purpose of saving the text, users often deleted the source text from the syscomments table to save disk space and to remove confidential information from this public area. However, you should not delete the source text because this may cause a problem for future upgrades of Adaptive Server. If you have removed the source text from syscomments, use the procedures in this section to restore the source text. Restoring source text If a compiled object does not have matching source text in the syscomments table, you can restore the source text to syscomments using any of the following methods: • Load the source text from a backup. • Re-create the source text manually. • Reinstall the application that created the compiled object. Verifying and encrypting source text Adaptive Server versions 11.5 and later allow you to verify the existence of source text, and encrypt the text if you choose. Use these commands when you are working with source text: • sp_checkresource – verifies that source text is present in syscomments for each compiled object. • sp_hidetext – encrypts the source text of a compiled object in the syscomments table to prevent casual viewing. • sp_helptext – displays the source text if it is present in syscomments, or notifies you of missing source text.Naming conventions 6 Adaptive Server Enterprise • dbcc checkcatalog – notifies you of missing source text. Naming conventions The characters recognized by Adaptive Server are limited in part by the language of the installation and the default character set. Therefore, the characters allowed in SQL statements and in the data contained in the server vary from installation to installation and are determined in part by definitions in the default character set. SQL statements must follow precise syntactical and structural rules, and can contain operators, constants, SQL keywords, special characters, and identifiers. Identifiers are objects within the server, such as database names or table names. Naming conventions vary for some parts of the SQL statement. Operator, constants, SQL keywords, and Transact-SQL extensions must adhere to stricter naming restrictions than identifiers, which themselves cannot contain operators and special characters. However, the data contained within the server can be named following more permissive rules. Figure 1-2 illustrates these relationships. Figure 1-2: Naming conventions governing SQL statements The sections that follow describe the sets of characters that can be used for each part of a statement. The section on identifiers also describes naming conventions for database objects. CHAPTER 1 SQL Building Blocks Transact-SQL User’s Guide 7 SQL data characters The set of SQL data characters is the larger set from which both SQL language characters and identifier characters are taken. Any character in Adaptive Server’s character set, including both single-byte and multibyte characters, can be used for data values. SQL language characters SQL keywords, Transact-SQL extensions, and special characters such as the comparison operators > and <, can be represented only by 7-bit ASCII values A–Z, a–z, 0–9, and the following ASCII characters: Table 1-1: ASCII characters used in SQL Identifiers Conventions for naming database objects apply throughout Adaptive Server software and documentation. Identifiers can be as many as 30 bytes in length, whether or not multibyte characters are used. The first character of an identifier must be declared as an alphabetic character in the character set definition in use on Adaptive Server. The @ sign or _(underscore character) can also be used. The @ sign as the first character of an identifier indicates a local variable. Temporary table names must either begin with # (the pound sign) if they are created outside tempdb or be preceded by “tempdb.”. Table names for temporary tables that exist outside tempdb should not exceed 13 bytes in length, including the number sign, since Adaptive Server gives them an internal numeric suffix. ; (semicolon) ( (open parenthesis) ) (close parenthesis) , (comma) : (colon) % (percent sign) - (minus sign) ? (question mark) ’ (single quote) " (double quote) + (plus sign) _ (underscore) * (asterisk) / (slash) (space) < (less than operator) > (greater than operator) = (equals operator) & (ampersand) | (vertical bar) ^ (circumflex) [ (left bracket) ] (right bracket) \ (backslash) @ (at sign) ~ (tilde) ! (exclamation point) $ (dollar sign) # (number sign) . (period)Naming conventions 8 Adaptive Server Enterprise After the first character, identifiers can include characters declared as alphabetic, numeric, or the character $, #, @, _, ¥ (yen), or £ (pound sterling). However, you cannot use two @@ symbols together at the beginning of a named object, as in “@@myobject.” This naming convention is reserved for global variables, which are system-defined variables that Adaptive Server updates on an ongoing basis. The case sensitivity of Adaptive Server is set when the server is installed and can be changed only by a System Administrator. To see the setting for your server, execute: sp_helpsort On a server that is not case-sensitive, the identifiers MYOBJECT, myobject, and MyObject (and all combinations of case) are considered identical. You can create only one of these objects, but you can use any combination of case to refer to that object. No embedded spaces are allowed in identifiers, and none of the SQL reserved keywords can be used. The reserved words are listed in the Adaptive Server Reference Manual. You can use the function valid_name to determine if an identifier you have created is acceptable to Adaptive Server. For example: select valid_name (“string") string is the identifier you want to check. If string is not valid as an identifier, Adaptive Server returns a 0 (zero). If string is a valid identifier, Adaptive Server returns a number other than 0. Adaptive Server returns a 0 if illegal characters are used or if string is longer than 30 bytes. Using multibyte character sets In multibyte character sets, a wider range of characters is available for use in identifiers. For example, on a server with the Japanese language installed, the following types of characters can be used as the first character of an identifier: Zenkaku or Hankaku Katakana, Hiragana, Kanji, Romaji, Cyrillic, Greek, or ASCII. Although Hankaku Katakana characters are legal in identifiers on Japanese systems, they are not recommended for use in heterogeneous systems. These characters cannot be converted between the EUC-JIS and Shift-JIS character sets. CHAPTER 1 SQL Building Blocks Transact-SQL User’s Guide 9 The same is true for some 8-bit European characters. For example, the character “Œ,” the OE ligature, is part of the Macintosh character set (code point 0xCE), but does not exist in the ISO 8859-1 (iso_1) character set. If “Œ” exists in data being converted from the Macintosh to the ISO 8859-1 character set, it causes a conversion error. If an object identifier contains a character that cannot be converted, the client loses direct access to that object. Delimited identifiers Delimited identifiers are object names enclosed in double quotes. Using delimited identifiers allows you to avoid certain restrictions on object names. You can use double quotes to delimit table, view, and column names; you cannot use them for other database objects. Delimited identifiers can be reserved words, can begin with non-alphabetic characters, and can include characters that would not otherwise be allowed. They cannot exceed 28 bytes. A pound sign (#) is illegal as a first character of any quoted identifier. (This restriction applies to Adaptive Server 11.5 and all later versions.) Before you create or reference a delimited identifier, you must execute: set quoted_identifier on This allows Adaptive Server to recognize delimited identifiers. Each time you use the quoted identifier in a statement, you must enclose it in double quotes. For example: create table "1one"(col1 char(3)) select * from "1one" create table "include spaces" (col1 int) Note Delimited identifiers cannot be used with bcp, may not be supported by all front-end products, and can produce unexpected results when used with system procedures. While the quoted_identifier option is turned on, do not use double quotes around character or date strings; use single quotes instead. Delimiting these strings with double quotes causes Adaptive Server to treat them as identifiers. For example, to insert a character string into col1 of 1table, use: insert "1one"(col1) values (’abc’) not:Naming conventions 10 Adaptive Server Enterprise insert "1one"(col1) values ("abc") To insert a single quote into a column, use two consecutive single quotation marks. For example, to insert the characters “a’b” into col1, use: insert "1one"(col1) values(’a’’b’) Syntax that includes quotes When the quoted_identifier option is set to on, you do not need to use double quotes around an identifier if the syntax of the statement requires that a quoted string contain an identifier. For example: create table '1one' (c1 int) The quotes are included in the name of table ’1one’: select object_id('1one') ----------------------- 896003192 You can include an embedded double quote in a quoted identifier by doubling the quote: create table "embedded""quote" (c1 int) However, there is no need to double the quote when the statement syntax requires the object name to be expressed as a string: select object_id('embedded"quote') Uniqueness and qualification conventions The names of database objects do not have to be unique in a database. However, column names and index names must be unique within a table, and other object names must be unique for each owner within a database. Database names must be unique in Adaptive Server. If you try to create a column using a name that is not unique in the table, or to create another database object, such as a table, a view, or a stored procedure, with a name that you have already used in the same database, Adaptive Server responds with an error message. You can uniquely identify a table or column by adding other names that qualify it. The database name, the owner’s name, and, for a column, the table name or view name may be used to create a unique ID. Each of these qualifiers is separated from the next by a period: For example, if the user “sharon” owns the authors table in the pubs2 database, the unique identifier of the city column in that table is: pubs2.sharon.authors.cityCHAPTER 1 SQL Building Blocks Transact-SQL User’s Guide 11 The same naming syntax applies to other database objects. You can refer to any object in a similar fashion: pubs2.dbo.titleview dbo.postalcoderule If the quoted_identifier option of the set command is on, you can use double quotes around individual parts of a qualified object name. Use a separate pair of quotes for each qualifier that requires quotes. For example, use: database.owner."table_name"."column_name" rather than: database.owner."table_name.column_name" The full naming syntax is not always allowed in create statements because you cannot create a view, procedure, rule, default, or trigger in a database other than the one you are currently in. The naming conventions are indicated in the syntax as: [[database.]owner.]object_name or [owner.]object_name The default value for owner is the current user, and the default value for database is the current database. When you reference an object in any SQL statement, other than a create statement, without qualifying it with the database name and owner name, Adaptive Server first looks at all the objects you own, and then at the objects owned by the Database Owner. As long as Adaptive Server is given enough information to identify an object, you need not type every element of its name. You can omit intermediate elements and indicate their positions with periods: database..table_name In the example above, you must include the starting element if you are using this syntax to create tables. If you omit the starting element, you would create a table named ..mytable. The naming convention prevents you from performing certain actions on such a table, such as cursor updates. When qualifying a column name and a table name in the same statement, use the same naming abbreviations for each; they are evaluated as strings and must match, or an error is returned. Here are two examples with different entries for the column name. The second example does not run because the syntax for the column name does not match the syntax for the table name. select pubs2.dbo.publishers.city from pubs2.dbo.publishersNaming conventions 12 Adaptive Server Enterprise city ----------------------- Boston Washington Berkeley select pubs2.sa.publishers.city from pubs2..publishers The column prefix "pubs2.sa.publishers" does not match a table name or alias name used in the query. Identifying remote servers You can execute stored procedures on a remote Adaptive Server. The results from the stored procedure display on the terminal that calls the procedure. The syntax for identifying a remote server and the stored procedure is: [execute] server.[database].[owner].procedure_name You can omit the execute keyword when the remote procedure call (RPC) is the first statement in a batch. If other SQL statements precede the RPC, you must use execute or exec. You must give the server name and the stored procedure name. If you omit the database name, Adaptive Server looks for procedure_name in your default database. If you give the database name, you must also give the procedure owner’s name, unless you own the procedure or the procedure is owned by the Database Owner. The following statements execute the stored procedure byroyalty in the pubs2 database located on the GATEWAY server: Statement Notes GATEWAY.pubs2.dbo.byroyalty GATEWAY.pubs2..byroyalty byroyalty is owned by the Database Owner. GATEWAY...byroyalty Use if pubs2 is the default database. declare @var int exec GATEWAY...byroyalty Use when the statement is not the first statement in a batch.CHAPTER 1 SQL Building Blocks Transact-SQL User’s Guide 13 See the System Administration Guide for information on setting up Adaptive Server for remote access. A remote server name (GATEWAY in the previous example) must match a server name in your local Adaptive Server’s interfaces file. If the server name in interfaces is in uppercase letters, you must also use uppercase letters in the RPC. Expressions in Adaptive Server An expression is a combination of one or more constants, literals, functions, column identifiers, and variables, separated by operators, that returns a single value. Expressions can be of several types, including arithmetic, relational, logical (or Boolean), and character string. In some Transact-SQL clauses, a subquery can be used in an expression. A case expression can be used in an expression. Use parentheses to group the elements in an expression. When “expression” is given as a variable in a syntax statement, a simple expression is assumed. “Logical expression” is specified when only a logical expression is acceptable. Arithmetic and character expressions The general pattern for arithmetic and character expressions is: {constant | column_name | function | (subquery) | (case_expression)} [{arithmetic_operator | bitwise_operator | string_operator | comparison_operator } {constant | column_name | function | (subquery) | case_expression}]... Operator precedence Operators have the following precedence levels, where 1 is the highest level and 6 is the lowest: 1 unary (single argument) - + ~ 2 * /% 3 binary (two argument) + - & | ^ 4 notExpressions in Adaptive Server 14 Adaptive Server Enterprise 5 and 6 or When all operators in an expression are of the same level, the order of execution is left to right. You can change the order of execution with parentheses—the most deeply nested expression is handled first. Arithmetic operators Adaptive Server uses these arithmetic operators: Table 1-2: Arithmetic operators You can use addition, subtraction, division, and multiplication on exact numeric, approximate numeric, and money type columns. Author comment: numeric added re CR 315018 4/17/03, rjoly You cannot use the modulo operator on smallmoney, money, float, numeric, or real columns. Modulo finds the integer remainder after a division involving two whole numbers. For example, 21% 11 = 10 because 21 divided by 11 equals 1 with a remainder of 10. When you perform arithmetic operations on mixed datatypes (for example, float and int) Adaptive Server follows specific rules for determining the type of the result. See Chapter 7, “Using and Creating Datatypes,” for more information. Bitwise operators The bitwise operators are a Transact-SQL extension for use with data of the type integer. These operators convert each integer operand into its binary representation and then evaluate the operands column by column. A value of 1 corresponds to true; a value of 0 corresponds to false. Operator Meaning + Addition – Subtraction * Multiplication / Division % Modulo (Transact-SQL extension) CHAPTER 1 SQL Building Blocks Transact-SQL User’s Guide 15 Table 1-3 and Table 1-4 summarize the results for operands of 0 and 1. If either operand is NULL, the bitwise operator returns NULL: Table 1-3: Truth tables for bitwise operations The following examples use two tinyint arguments: A = 170 (10101010 in binary form) and B = 75 (01001011 in binary form). Table 1-4: Examples of bitwise operations & (and) 1 0 1 1 0 0 0 0 | (or) 1 0 1 1 1 0 1 0 ^ (exclusive or) 1 0 1 0 1 0 1 0 ~ (not) 1 FALSE 0 0 Operation Binary form Result Explanation (A & B) 10101010 01001011 ------------ 00001010 10 Result column equals 1 if both A and B are 1. Otherwise, result column equals 0. (A | B) 10101010 01001011 ------------ 11101011 235 Result column equals 1 if either A or B, or both, is 1. Otherwise, result column equals 0. (A ^ B) 10101010 01001011 ------------ 11100001 225 Result column equals 1 if either A or B, but not both, is 1.Expressions in Adaptive Server 16 Adaptive Server Enterprise The String concatenation operator The string operator + can concatenate two or more character or binary expressions. For example: select Name = (au_lname + ", " + au_fname) from authors Displays author names under the column heading “Name” in last-name, first-name order, with a comma after the last name; for example, “Bennett, Abraham.” select "abc" + "" + "def" Returns the string “abc def”. The empty string is interpreted as a single space in all char, varchar, nchar, nvarchar, and text concatenation, and in varchar insert and assignment statements. When concatenating non-character, non-binary expressions, use convert: select "The date is " + convert(varchar(12), getdate()) The comparison operators Adaptive Server uses these comparison operators: (~A) 10101010 ------------ 01010101 85 All 1s are changed to 0s and all 0s to 1s. Operation Binary form Result ExplanationCHAPTER 1 SQL Building Blocks Transact-SQL User’s Guide 17 Table 1-5: Comparison operators In comparing character data, < means closer to the beginning of the server’s sort order and > means closer to the end of the sort order. Uppercase and lowercase letters are equal in a sort order that is not case sensitive. Use sp_helpsort to see the sort order for your Adaptive Server. Trailing blanks are ignored for comparison purposes. In comparing dates, < means earlier than and > means later than. Put single or double quotes around all character and date and time data used with a comparison operator: = "Bennet" > "May 22 1947" Nonstandard operators The following operators are Transact-SQL extensions: • Modulo operator: % • Negative comparison operators: !>, !<, != • Bitwise operators: ~, ^, |, & • Join operators: *= and =* Operator Meaning = Equal to > Greater than < Less than >= Greater than or equal to <= Less than or equal to <> Not equal to != Not equal to (Transact-SQL extension) !> Not greater than (Transact-SQL extension) !< Not less than (Transact-SQL extension) Expressions in Adaptive Server 18 Adaptive Server Enterprise Comparing character expressions Adaptive Server treats character constant expressions as varchar. If they are compared with non-varchar variables or column data, the datatype precedence rules are used in the comparison (that is, the datatype with lower precedence is converted to the datatype with higher precedence). If implicit datatype conversion is not supported, you must use the convert function. See the Reference Manual for more information on supported and unsupported conversions. Comparison of a char expression to a varchar expression follows the datatype precedence rule; the “lower” datatype is converted to the “higher” datatype. All varchar expressions are converted to char (that is, trailing blanks are appended) for the comparison. Using the empty string The empty string (“”) or (‘’) is interpreted as a single blank in insert or assignment statements on varchar data. When varchar, char, nchar, or nvarchar data is concatenated, the empty string is interpreted as a single space. For example, this is stored as “abc def”: "abc" + "" + "def" The empty string is never evaluated as NULL. Including quotation marks in character expressions There are two ways to specify literal quotes within a char or varchar entry. The first method is to use an additional quote with a quote of the same type. This is called “escaping” the quote. For example, if you begin a character entry with a single quote, but you want to include a single quote as part of the entry, use two single quotes: ’I don’t understand.’ Here is an example containing internal double and single quotes. The single quote does not have to be escaped, but the double quote does: "He said, ""It’s not really confusing.""" The second method is to enclose a quote in the opposite kind of quotation mark. In other words, surround an entry containing a double quote with single quotes (or vice versa). Here are some examples: ’George said, "There must be a better way."’ "Isn’t there a better way?" CHAPTER 1 SQL Building Blocks Transact-SQL User’s Guide 19 ’George asked, "Isn”t there a better way?"’ To continue a character string that would go off the end of one line on your screen, enter a backslash (\) before going to the following line. Note If the quoted_identifier option is set to on, do not use double quotes around character or date data. You must use single quotes, or Adaptive Server treats the data as an identifier. For more information about quoted identifiers, see “Delimited identifiers” on page 9. Relational and logical expressions A logical expression or relational expression returns TRUE, FALSE, or UNKNOWN. The general patterns are: expression comparison_operator [any | all] expression expression [not] in expression [not] exists expression expression [not] between expression and expression expression [not] like “match_string" [escape "escape_character"] not expression like "match_string" [escape "escape_character"] expression is [not] null not logical_expression logical_expression {and | or} logical_expression Using any, all, and in any is used with <, >, or = and a subquery. It returns results when any value retrieved in the subquery matches the value in the where or having clause of the outer statement. all is used with < or > and a subquery. It returns results when all values retrieved in the subquery are less than (<) or greater than (>) the value in the where or having clause of the outer statement. See Chapter 4, “Subqueries: Using Queries Within Other Queries,” for more information. in returns results when any value returned by the second expression matches the value in the first expression. The second expression must be a subquery or a list of values enclosed in parentheses. in is equivalent to = any. Transact-SQL extensions 20 Adaptive Server Enterprise Connecting expressions with and and or and connects two expressions and returns results when both are true. or connects two or more conditions and returns results when either of the conditions is true. When more than one logical operator is used in a statement, and is evaluated before or. Use parentheses to change the order of execution. Table 1-6 shows the results of logical operations, including those that involve null values: Table 1-6: Truth tables for logical expressions The result UNKNOWN indicates that one or more of the expressions evaluates to NULL, and that the result of the operation cannot be determined to be either TRUE or FALSE. Transact-SQL extensions Transact-SQL enhances the power of SQL and minimizes the occasions on which users must resort to a programming language to accomplish a desired task. Transact-SQL’s capabilities go beyond the ISO standards and the many commercial versions of SQL. and TRUE FALSE NULL TRUE TRUE FALSE UNKNOWN FALSE FALSE FALSE FALSE NULL UNKNOWN FALSE UNKNOWN or TRUE FALSE NULL TRUE TRUE TRUE TRUE FALSE TRUE FALSE UNKNOWN NULL TRUE UNKNOWN UNKNOWN not TRUE FALSE FALSE TRUE NULL UNKNOWNCHAPTER 1 SQL Building Blocks Transact-SQL User’s Guide 21 Most of the Transact-SQL enhancements (known as extensions) are summarized here. The Transact-SQL extensions for each command are in the Reference Manual. The compute clause The Transact-SQL compute clause extension is used with the row aggregate functions sum, max, min, avg, and count to calculate summary values. Queries that include a compute clause display results with both detail and summary rows. These reports resemble those produced by almost any Database Management System (DBMS) with a report generator. compute displays summary values as additional rows in the results, instead of as new columns. The compute clause is covered in Chapter 3, “Using Aggregates, Grouping, and Sorting.” Control-of-flow language Transact-SQL provides control-of-flow language that can be used as part of any SQL statement or batch. These constructs are available: begin...end, break, continue, declare, goto label, if...else, print, raiserror, return, waitfor, and while. Local variables can be defined with declare and assigned values. A number of predefined global variables are supplied by the system. Transact-SQL also supports case expressions, which include the keywords case, when, then, coalesce, and nullif. case expressions replace the if statements of standard SQL. case expressions are allowed anywhere a value expression is used. Stored procedures One of the most important Transact-SQL extensions is the ability to create stored procedures. A stored procedure is a collection of SQL statements and optional control-of-flow statements stored under a name. The creator of a stored procedure can also define parameters to be supplied when the stored procedure is executed. Transact-SQL extensions 22 Adaptive Server Enterprise The ability to write your own stored procedures greatly enhances the power, efficiency, and flexibility of the SQL database language. Since the execution plan is saved after stored procedures are run, stored procedures can subsequently run much faster than standalone statements. Adaptive Server-supplied stored procedures, called system procedures, aid in Adaptive Server system administration. Chapter 15, “Using Stored Procedures,” discusses system procedures and explains how to create stored procedures. System procedures are discussed in detail in the Reference Manual. Users can execute stored procedures on remote servers. All Transact-SQL extensions support return values from stored procedures, user-defined return status from stored procedures, and the ability to pass parameters from a procedure to its caller. Extended stored procedures An extended stored procedure (ESP) has the interface of a stored procedure, but instead of containing SQL statements and control-of-flow statements, it executes procedural language code that has been compiled into a dynamic link library (DLL). The procedural language in which an ESP function is written can be any language capable of calling C language functions and manipulating C datatypes. ESPs allow Adaptive Server to perform a task outside the RDBMS in response to an event occurring within the database. For example, you could use an ESP to send an e-mail notification or network-wide broadcast in response to an event occurring within the Relational Database Management System (RDBMS). There are some Adaptive Server-supplied ESPs, called system extended stored procedures. One of these, xp_cmdshell, allows you to execute an operating system command from within Adaptive Server. Chapter 16, “Using Extended Stored Procedures,” describes ESPs. The Reference Manual includes detailed information about system ESPs. ESPs are implemented by an Open Server™ application called XP Server™, which runs on the same machine as Adaptive Server. Remote execution of a stored procedure is called a remote procedure call (RPC). Adaptive Server and XP Server communicate through RPCs. XP Server is automatically installed with Adaptive Server.CHAPTER 1 SQL Building Blocks Transact-SQL User’s Guide 23 Triggers A trigger is a stored procedure that instructs the system to take one or more actions when a specific change is attempted. By preventing incorrect, unauthorized, or inconsistent changes to data, triggers help maintain the integrity of a database. Triggers can also protect referential integrity—enforcing rules about the relationships among data in different tables. Triggers go into effect when a user attempts to modify data with an insert, delete, or update command. Triggers can nest to a depth of 16 levels, and can call local or remote stored procedures or other triggers. Defaults and rules Transact-SQL provides keywords for maintaining entity integrity (ensuring that a value is supplied for every column requiring one) and domain integrity (ensuring that each value in a column belongs to the set of legal values for that column). Defaults and rules define integrity constraints that come into play during data entry and modification. A default is a value linked to a particular column or datatype, and inserted by the system if no value is provided during data entry. Rules are user-defined integrity constraints linked to a particular column or datatype, and enforced at data entry time. Rules and defaults are discussed in Chapter 13, “Defining Defaults and Rules for Data.” Error handling and set options A number of error handling techniques are available to the Transact-SQL programmer, including the ability to capture return status from stored procedures, define customized return values from stored procedures, pass parameters from a procedure to its caller, and get reports from global variables such as @@error. The raiserror and print statements, in combination with control-of-flow language, can direct error messages to the user of a TransactSQL application. Developers can localize print and raiserror to use different languages. set options customize the display of results, show processing statistics, and provide other diagnostic aids for debugging your Transact-SQL programs. All set options except showplan and char_convert take effect immediately. Transact-SQL extensions 24 Adaptive Server Enterprise The following paragraphs list the available set options. For more information, refer to the Reference Manual. • parseonly, noexec, prefetch, showplan, rowcount, nocount, and tablecount control the way a query is executed. The statistics options display performance statistics after each query. flushmessage determines when Adaptive Server returns messages to the user. See the Performance and Tuning Guide for more information. • arithabort determines whether Adaptive Server aborts queries with arithmetic overflow and numeric truncation errors. arithignore determines whether Adaptive Server prints a warning message if a query results in an arithmetic overflow. For more information, see “Arithmetic errors” on page 29. • offsets and procid are used in DB-Library™ to interpret results from Adaptive Server. • datefirst, dateformat, and language affect date functions, date order, and message display. • char_convert controls character-set conversion between Adaptive Server and a client. • textsize controls the size of text or image data returned with a select statement. See “Text functions used for text and image data” on page 389. • cursor rows and close on endtran affect the way Adaptive Server handles cursors. See “Fetching data rows using cursors” on page 604. • identity_insert allows or prohibits inserts that affect a table’s IDENTITY column. See “Gaps due to insertions, deletions, identity grab size, and rollbacks” on page 261. • chained and transaction isolation level control how Adaptive Server handles transactions. See “Selecting the transaction mode and isolation level” on page 641. • self_recursion allows Adaptive Server to handle triggers that cause themselves to fire. See “Trigger self-recursion” on page 580. • ansinull, ansi_permissions, and fipsflagger control whether Adaptive Server flags the use of nonstandard SQL. string_rtruncation controls whether Adaptive Server raises an exception error when truncating a char or nchar string. See “Compliance to ANSI standards” on page 26. CHAPTER 1 SQL Building Blocks Transact-SQL User’s Guide 25 • quoted_identifier controls whether Adaptive Server treats character strings enclosed in double quotes as identifiers. See “Delimited identifiers” on page 9 for more information. • role controls the roles granted to you. For information about roles, see the System Administration Guide. Additional Adaptive Server extensions to SQL Other unique or unusual features of Transact-SQL include: • The following extensions to SQL search conditions: modulo operator (%), negative comparison operators (!>, !<, and !=), bitwise operators (–, ^, |, and &), join operators (*= and =*), wildcard characters ([ ] and -), and the not operator (^). See Chapter 2, “Queries: Selecting Data from a Table.” • Fewer restrictions on the group by clause and the order by clause. See Chapter 3, “Using Aggregates, Grouping, and Sorting.” • Subqueries, which can be used almost anywhere an expression is allowed. See Chapter 4, “Subqueries: Using Queries Within Other Queries.” • Temporary tables and other temporary database objects, which exist only for the duration of the current work session, and disappear thereafter. See Chapter 8, “Creating Databases and Tables.” • User-defined datatypes built on Adaptive Server-supplied datatypes. See Chapter 7, “Using and Creating Datatypes,” and Chapter 13, “Defining Defaults and Rules for Data.” • The ability to insert data from a table into that same table. See Chapter 9, “Adding, Changing, and Deleting Data.” • The ability to extract data from one table and put it into another with the update command. See Chapter 9, “Adding, Changing, and Deleting Data.” • The ability to remove data based on data in other tables using the join in a delete statement. See Chapter 9, “Adding, Changing, and Deleting Data.” • A fast way to delete all rows in a specified table and reclaim the space they took up with the truncate table command. See Chapter 9, “Adding, Changing, and Deleting Data.” • IDENTITY columns, which provide system-generated values that uniquely identify each row within a table. See Chapter 9, “Adding, Changing, and Deleting Data.”Compliance to ANSI standards 26 Adaptive Server Enterprise • Updates and selections through views. Unlike most other versions of SQL, Transact-SQL places no restrictions on retrieving data through views, and few restrictions on updating data through views. See Chapter 10, “Views: Limiting Access to Data.” • Dozens of built-in functions. See Chapter 11, “Using the Built-In Functions in Queries.” • Options to the create index command for fine-tuning aspects of performance determined by indexes, and controlling the treatment of duplicate keys and rows. See Chapter 12, “Creating Indexes on Tables.” • Control over what happens when a user attempts to enter duplicate keys in a unique index, or duplicate rows in a table. See Chapter 12, “Creating Indexes on Tables.” • Bitwise operators for use with integer and bit type columns. See “Bitwise operators” on page 49 and Chapter 7, “Using and Creating Datatypes.” • Support for text and image datatypes. See Chapter 7, “Using and Creating Datatypes.” • The ability to gain access to both Sybase and non-Sybase databases. With Component Integration Services, you can accomplish the following types of actions between tables in remote, heterogeneous servers: access remote tables as if they were local, perform joins, transfer data between tables, maintain referential integrity, provide applications such as PowerBuilder® with transparent access to heterogeneous data, and use native remote server capabilities. For more information, see the Component Integration Services User’s Guide. Compliance to ANSI standards The progression of standards for relational database management systems is ongoing. These standards have been, and are being, adopted by ISO and several national standards bodies. SQL86 was the first of these standards. This was replaced by SQL89, which in turn was replaced by SQL92, which is the current standard. SQL92 defines three levels of conformance: entry, intermediate, and full. In the United States, the National Institute for Standards and Technology (NIST) has defined the transitional level, which falls between the entry and intermediate levels.CHAPTER 1 SQL Building Blocks Transact-SQL User’s Guide 27 Certain behaviors defined by the standards are not compatible with existing SQL Server and Adaptive Server applications. Transact-SQL provides set options that allow you to toggle these behaviors. By default, compliant behavior is enabled for all Embedded SQL™ precompiler applications. Other applications needing to match SQL standard behavior can use the options in Table 1-7 for entry-level SQL92 compliance. For more information on setting these options, see set in the Reference Manual. Table 1-7: Set command flags for entry-level SQL92 compliance The following sections describe the differences between standard behavior and default Transact-SQL behavior. Federal Information Processing Standards (FIPS) flagger For customers writing applications that must conform to the SQL92 standard, Adaptive Server provides a set fipsflagger option. When this option is turned on, all commands containing Transact-SQL extensions that are not allowed in entry-level SQL92 generate an informational message. This option does not disable the extensions. Processing completes when you issue the non-ANSI SQL command. Option Setting ansi_permissions on ansinull on arithabort off arithabort numeric_truncation on arithignore off chained on close on endtran on fipsflagger on quoted_identifier on string_rtruncation on transaction isolation level 3Compliance to ANSI standards 28 Adaptive Server Enterprise Chained transactions and isolation levels Adaptive Server provides SQL standard-compliant “chained” transaction behavior as an option. In chained mode, all data retrieval and modification commands (delete, insert, open, fetch, select, and update) implicitly begin a transaction. Since such behavior is incompatible with many Transact-SQL applications, Transact-SQL style (or “unchained”) transactions remain the default. You can initiate chained transaction mode using the set chained option. The set transaction isolation level option controls transaction isolation levels. See Chapter 19, “Transactions: Maintaining Data Consistency and Recovery,” for more information. Identifiers To be compliant with entry-level SQL92, identifiers cannot: • Begin with a pound sign (#) • Have more than 18 characters • Contain lowercase letters Delimited identifiers Adaptive Server supports delimited identifiers for table, view, and column names. Delimited identifiers are object names enclosed within double quotation marks. Using them allows you to avoid certain restrictions on object names. Use the set quoted_identifier option to recognize delimited identifiers. When this option is on, all characters enclosed in double quotes are treated as identifiers. Because this behavior is incompatible with many existing applications, the default setting for this option is off. SQL standard-style comments In Transact-SQL, comments are delimited by “/*” and “*/”, and can be nested. Transact-SQL also supports SQL standard-style comments, which consist of any string beginning with two connected minus signs, a comment, and a terminating new line:CHAPTER 1 SQL Building Blocks Transact-SQL User’s Guide 29 select "hello" -- this is a comment The Transact-SQL “/*” and “*/” comment delimiters are fully supported, but “--” within Transact-SQL comments is not recognized. Right truncation of character strings The string_rtruncation set option controls silent truncation of character strings for SQL standard compatibility. Set this option to on to prohibit silent truncation and enforce SQL standard behavior. Permissions required for update and delete statements The ansi_permissions set option determines permissions required for delete and update statements. When this option is on, Adaptive Server uses the more stringent SQL92 permission requirements for these statements. Because this behavior is incompatible with many existing applications, the default setting for this option is off. Arithmetic errors The arithabort and arithignore set options allow compliance with the SQL92 standard as follows: • arithabort arith_overflow specifies behavior following a divide-by-zero error or a loss of precision. The default setting, arithabort arith_overflow on, rolls back the entire transaction in which the error occurs. If the error occurs in a batch that does not contain a transaction, arithabort arith_overflow on does not roll back earlier commands in the batch, but Adaptive Server does not execute statements in the batch that follow the error-generating statement. If you set arithabort arith_overflow off, Adaptive Server aborts the statement that causes the error but continues to process other statements in the transaction or batch.Compliance to ANSI standards 30 Adaptive Server Enterprise • arithabort numeric_truncation specifies behavior following a loss of scale by an exact numeric type. The default setting, on, aborts the statement that causes the error but continues to process other statements in the transaction or batch. If you set arithabort numeric_truncation off, Adaptive Server truncates the query results and continues processing. For compliance with the SQL92 standard, enter set arithabort numeric_truncation on. • arithignore arith_overflow determines whether Adaptive Server displays a message after a divide-by-zero error or a loss of precision. The default setting, off, displays a warning message after these errors. Setting arithignore arith_overflow on suppresses warning messages after these errors. For compliance to the SQL92 standard, enter set arithignore off. Synonymous keywords Several keywords added for SQL standard compatibility are synonymous with existing Transact-SQL keywords. Table 1-8: ANSI-compatible keyword synonyms Treatment of nulls The set option ansinull determines whether or not evaluation of null-valued operands in SQL equality (=) or inequality (!=) comparisons and aggregate functions is SQL standard-compliant. This option does not affect how Adaptive Server evaluates null values in other kinds of SQL statements such as create table. Current syntax Additional syntax commit tran, commit transaction rollback tran, rollback transaction commit work rollback work any some grant all grant all privileges revoke all revoke all privileges max (expression) max ([all | distinct]) expression min (expression) min ([all | distinct]) expression user_name() built-in function user keywordCHAPTER 1 SQL Building Blocks Transact-SQL User’s Guide 31 Adaptive Server login accounts Each Adaptive Server user must have a login account identified by a unique login name and a password. The account is established by a System Security Officer. Login accounts have the following characteristics: • A login name, unique on that server. • A password. • A default database (optional). If a default is defined, the user starts each Adaptive Server session in the defined database without having to issue the use command. If no default is defined, each session starts in the master database. • A default language (optional). This specifies the language in which prompts and messages display. If a language is not defined, Adaptive Server’s default language, which is set at installation, is used. • A full name (optional). This is your full name, which can be useful for documentation and identification purposes. Group membership In Adaptive Server, you can use groups to grant and revoke permissions to more than one user at a time within a database. For example, if everyone who works in the “Sales” department needs access to certain tables, all of those users can be put into a group called “sales”. The Database Owner can grant specific access permissions to that group rather than having to grant permission to each user individually. A group is created within a database, not on the server as a whole. The Database Owner is responsible for creating groups and assigning users to them. You are always a member of the “public” group, which includes all users on Adaptive Server. You can also belong to one other group. You can use sp_helpuser to find out what group you are a member of: sp_helpuser user_nameAdaptive Server login accounts 32 Adaptive Server Enterprise Role membership In Adaptive Server, a System Security Officer can define and create roles as a convenient way to grant and revoke permissions to several users at a time, server-wide. For example, clerical staff may need to be able to insert and select from tables in several databases, but they may not need to update them. A System Security Officer could define a role called “clerical_user_role” and grant the role to everyone in the clerical staff. Database object owners could then grant “clerical_user_role” the required privileges. Roles can be defined in a role hierarchy, where a role such as “office_manager_role” contains the “clerical_user_role”. Users who are granted roles in a hierarchy automatically have all the permissions of the roles that are lower in the hierarchy. For example, the Office Manager can perform all the actions permitted for the clerical staff. Hierarchies can include either system or user-defined roles. To find out more about roles assigned to you use: • sp_displayroles – to find out all roles assigned to you, whether or not they are active. • sp_activeroles – to find out which of your assigned roles are active. If you specify the expand_down parameter, Adaptive Server displays any roles contained within your currently active roles. The syntax is: sp_displayroles user_name sp_activeroles expand_down For more information about roles, see the System Administration Guide. Getting information about your Adaptive Server account You can get information about your own Adaptive Server login account by using: sp_displaylogin Adaptive Server returns the following information: • Your server user ID • Your login name • Your full nameCHAPTER 1 SQL Building Blocks Transact-SQL User’s Guide 33 • Any roles granted to you (regardless of whether they are currently active) • Whether your account is locked • The date you last changed your password Changing your password It is a good idea to change your password periodically. The System Security Officer can configure Adaptive Server to require that you change your password at preset, regular intervals. If this is the case on your server, Adaptive Server notifies you when it is time to change your password. Note If you use remote servers, you must change your password on all remote servers that you access before you change it on your local server. For more information, see “Changing your password on a remote server” on page 35. You can change your password at any time using sp_password: sp_password old_passwd, new_passwd When you create a new password: • It must be at least six bytes long. • It can be any printable letters, numbers, or symbols. • The maximum size for a password is 30 bytes. If your password exceeds 30 bytes, Adaptive Server uses only the first 30 characters. When you specify a password, enclose it in quotation marks if: • It includes characters other than A–Z, a–z, 0–9, _, #, valid single-byte or multibyte alphabetic characters, or accented alphabetic characters. • It begins with a number 0–9. The following example shows how to change the password “terrible2” to “3blindmice”: sp_password terrible2, "3blindmice" A return status of 0 means that the password was changed. For more information about sp_password, see the Reference Manual. Adaptive Server login accounts 34 Adaptive Server Enterprise Understanding remote logins You can execute stored procedures on a remote Adaptive Server using RPCs if you have been granted access to the remote server and an appropriate database on that server. Remote execution of a stored procedure is a remote procedure call (RPC). To obtain access to a remote server: • The remote server must be known to your local server. This occurs when the System Security Officer executes sp_addserver. • You must acquire a login on the remote server. This happens when the System Administrator executes sp_addremotelogin. • You must be added as a user to the appropriate database on the remote server. This is accomplished when the Database Owner executes sp_adduser. These procedures are discussed in the System Administration Guide. When you can access the remote server, you can execute an RPC by qualifying the stored procedure name with the name of the remote server. For example, to execute sp_help on the GATEWAY server, enter: GATEWAY...sp_help Or, to fully qualify the name of the procedure, include the name of the database containing the procedure and the name of its owner: GATEWAY.sybsystemprocs.dbo.sp_help In addition, if a System Security Officer has set up the local and remote servers to use network-based security services, one or more of the following functions may be in effect when you execute RPCs: • Mutual authentication – the local server authenticates the remote server by retrieving the credential of the remote server and verifying it with the security mechanism. With this service, the credentials of both servers are authenticated and verified. • Message confidentiality via encryption – messages are encrypted when sent to the remote server, and results from the remote server are encrypted. • Message integrity – messages between the servers are checked for tampering.CHAPTER 1 SQL Building Blocks Transact-SQL User’s Guide 35 If you are using the unified login feature of network-based security, a System Security Officer can use sp_remoteoption on the remote server to establish you as a trusted user who does not need to supply a password to the remote server. If you are using Open Client™ Client-Library™/C, you can use ct_remote_pwd to specify a password for the remote server. For more information about network-based security services, see the System Administration Guide. Changing your password on a remote server You must change your password on all remote servers that you access before you change it on your local server. If you change it on the local server first, when you issue the RPC to execute sp_password on the remote server, the command fails because your local and remote passwords do not match. The syntax for changing your password on the remote server is: remote_server...sp_password old_passwd, new_passwd For example: GATEWAY...sp_password terrible2, "3blindmice" For information on changing your password on the local server, review “Changing your password” on page 33. How to use Transact-SQL with the isql utility You can use Transact-SQL directly from the operating system with the standalone utility program isql. You must first set up an account, or login, on Adaptive Server. To use isql, type a command similar to the following at your operating system prompt: isql -Uhoratio -Ptallahassee -Shaze -w300 where “horatio” is the user, “tallahassee” is the password, and “haze” is the name of the Adaptive Server to which you are connecting. The -w parameter displays isql output at a width of 300 characters. Login names and passwords are case-sensitive. How to use Transact-SQL with the isql utility 36 Adaptive Server Enterprise If you start isql without using a login name, Adaptive Server assumes that your login name is the same as your operating system name. For details about specifying your server login name and other parameters for isql, see the Utility Programs manual for your platform. Note Do not use the -P option to isql to specify your password, because another user might see your password. After you start isql, you see: 1> You can now start issuing Transact-SQL commands. To connect to a non-Sybase database using Component Integration Services, use the connect to command. For more information, see the Component Integration Services User’s Guide. See also connect to...disconnect in the Reference Manual. Default databases When your Adaptive Server account was created, you may have been assigned a default database to which you are connected when you log in. For example, your default database might be pubs2, the sample database. If you were not assigned a default database, you are connected to the master database. You can change your default database to any database that you have permission to use, or to any database that allows guests. Any user with an Adaptive Server login can be a guest. To change your default database, use sp_modifylogin, which is described in the Reference Manual. To change to the pubs2 database, which is used for most examples in this manual, enter: 1> use pubs2 2> go Enter the word “go” on a line by itself and do not precede it with blanks or tabs. It is the command terminator; it lets Adaptive Server know that you have finished typing, and you are ready for your command to be executed. In general, examples of Transact-SQL statements shown in this manual do not include the line prompts used by the isql utility, nor do they include the terminator go. CHAPTER 1 SQL Building Blocks Transact-SQL User’s Guide 37 Using network-based security services with isql You can specify the -V option of isql to use network-based security services such as unified login. With unified login, you can be authenticated with a security mechanism offered by a third-party provider and then log in to Adaptive Server without specifying a login name or a password. Other security services you can use, if they are supported by the third-party security mechanism, include: • Data confidentiality • Data integrity • Mutual authentication • Data origin checking • Data replay detection • Out-of-sequence detection See the System Administration Guide for more information about the options you can specify to use network-based security. Logging out of isql You can log out of isql at any time by typing: quit or exit Either of these commands returns you to the operating system prompt, and do not require the terminator “go”. For more details on isql, see the Utility Guide. Using the pubs2 and pubs3 sample databases The pubs2 sample database is used for most examples in this manual. Where noted, the pubs3 database is used instead. You can try any of the examples on your own workstation. Using the pubs2 and pubs3 sample databases 38 Adaptive Server Enterprise The query results you see on your screen may not look exactly as they do in this manual. That is because some of the examples here have been reformatted (for example, the columns have been realigned) for visual clarity or to take up less space on the page. To change the sample database using create or data modification statements, you may need to get additional permissions from a System Administrator. If you do change the sample database, Sybase suggests that you return it to its original state for the sake of future users. Ask a System Administrator if you need help restoring the sample databases. What is in the sample databases? The sample database, pubs2, contains these tables: publishers, authors, titles, titleauthor, roysched, sales, salesdetail, stores, discounts, au_pix, and blurbs. The pubs3 sample database adds store_employees but does not include au_pix. pubs3 is an updated version of pubs2 and can be used for referential integrity examples. Its tables differ slightly from the tables defined in pubs2. Here is a brief description of each table: • publishers contains the identification numbers, names, cities, and states of three publishing companies. • authors contains an identification number, first and last name, address information, and contract status for each author. • titles contains the book ID, name, type, publisher ID, price, advance, royalty, year-to-date sales, comments, and publication date for each book. • titleauthor links the titles and authors tables together. It contains each book’s title ID, author ID, author order, and the royalty split among the authors of a book. • roysched lists the unit sales ranges and the royalty connected with each range. The royalty is some percentage of the net receipts from sales. • sales records the store ID, order number, and date of book sales. It acts as the master table for the detail rows in salesdetail. • salesdetail records the bookstore sales of titles in the titles table. • stores lists bookstores by store ID. • store_employees lists employees for the stores described in the stores table.CHAPTER 1 SQL Building Blocks Transact-SQL User’s Guide 39 • discounts lists three types of discounts for bookstores. • au_pix contains pictures of the authors in binary form using the image datatype. au_pix is in pubs2 only. • blurbs contains long book descriptions using the text datatype. The pubs2 database is illustrated in Appendix A, “The pubs2 Database,” while pubs3 is illustrated in Appendix B, “The pubs3 Database.”Using the pubs2 and pubs3 sample databases 40 Adaptive Server EnterpriseTransact-SQL User’s Guide 41 C H A P T E R 2 Queries: Selecting Data from a Table The select command retrieves data stored in the rows and columns of database tables using a procedure called a query. A query has three main parts: the select clause, the from clause, and the where clause. This chapter explains queries, provides examples, and discusses: This chapter focuses on basic single-table select statements. Many sections contain sample statements that you can use to practice writing queries. If you want to integrate other Transact-SQL functionality, such as joins, subqueries, and aggregates, you can find more complex query examples later in this book. What are queries? A SQL query requests data from the database and receives the results. This process, also known as data retrieval, is expressed using the select statement. You can use it for selections, which retrieve a subset of the rows in one or more tables, and you can use it for projections, which retrieve a subset of the columns in one or more tables. A simple example of a select statement is: select select_list from table_list where search_conditions Topic Page What are queries? 41 Choosing columns: the select clause 44 Eliminating duplicate query results with distinct 55 Specifying tables: the from clause 57 Selecting rows: the where clause 58 Pattern matching 65What are queries? 42 Adaptive Server Enterprise The select clause specifies the columns you want to retrieve. The from clause specifies the tables to search. The where clause specifies which rows in the tables you want to see. For example, the following select statement finds the first and the last names of writers living in Oakland from the authors table, in the pubs2 database. select au_fname, au_lname from authors where city = "Oakland" Results of this query appear in columnar format: au_fname au_lname -------------- ----------- Marjorie Green Dick Straight Dirk Stringer Stearns MacFeather Livia Karsen (5 rows affected) select syntax The select syntax can be simpler or more complex than shown in the previous example. A simple select statement contains only the select clause; the from clause is almost always included, but is necessary only in select statements that retrieve data from tables. All other clauses, including the where clause, are optional. The full syntax of the select statement includes these phrases and keywords: select [all | distinct] select_list [into [[database.]owner.] table_name] [from [[database.]owner.]{view_name|table_name [(index {index_name | table_name} [parallel [degree_of_parallelism] ] [prefetch size] [lru | mru])]} [holdlock | noholdlock] [shared] [,[[database.]owner.]{view_name| table_name [(index {index_name | table_name} [parallel [degree_of_parallelism] ] [prefetch size] [lru | mru])]} [holdlock | noholdlock] [shared]]...] [where search_conditions] [group by [all] aggregate_free_expressionCHAPTER 2 Queries: Selecting Data from a Table Transact-SQL User’s Guide 43 [, aggregate_free_expression]...] [having search_conditions] [order by {[[[database.]owner.]{table_name.|view_name.}] column_name | select_list_number | expression} [asc | desc] [,{[[[database.]owner.]{table_name|view_name.}] column_name | select_list_number | expression} [asc | desc]]...] [compute row_aggregate(column_name) [, row_aggregate(column_name)]... [by column_name [, column_name]...]] [for {read only | update [of column_name_list]}] [at isolation {read uncommitted | read committed | serializable}] [for browse] Use the clauses in a select statement in the order shown above. For example, if the statement includes a group by clause and an order by clause, the group by clause must precede the order by clause. Qualify the names of database objects if there is ambiguity about which object is being referred to. If several columns in multiple tables are called “name”, you may have to qualify “name” with the database name, owner name, or table name. For example: select au_lname from pubs2.dbo.authors Since the examples in this chapter involve single-table queries, column names in syntax models and examples are usually not qualified with the names of the tables, owners, or databases to which they belong. These elements are left out for readability; it is never wrong to include qualifiers. The remaining sections in this chapter analyze the syntax of the select statement in more detail. This chapter describes only some of the clauses and keywords included in the syntax of the select command. The following clauses are discussed in other chapters: • group by, having, order by, and compute are described in Chapter 3, “Using Aggregates, Grouping, and Sorting.” • into is described in Chapter 8, “Creating Databases and Tables.” • at isolation is described in Chapter 19, “Transactions: Maintaining Data Consistency and Recovery.”Choosing columns: the select clause 44 Adaptive Server Enterprise The holdlock, noholdlock, and shared keywords (which deal with locking in Adaptive Server) and the index clause are described in the Performance and Tuning Guide. For information about the for read only and for update clauses, see the declare cursor command in the Reference Manual. Note The for browse clause is used only in DB-Library applications. See the Open Client DB-Library/C Reference Manual for details. See also “Using browse mode instead of cursors” on page 618. Choosing columns: the select clause The items in the select clause make up the select list. When the select list consists of a column name, a group of columns, or the wildcard character (*), the data is retrieved in the order in which it is stored in the table (create table order). Choosing all columns: select * The asterisk (*) selects all the column names in all the tables specified by the from clause. Use it to save typing time and errors when you want to see all the columns in a table. * retrieves the data in create table order. The syntax for selecting all the columns in a table is: select * from table_list The following statement retrieves all columns in the publishers table and displays them in create table order. This statement retrieves all rows since it contains no where clause: select * from publishers The results look like this: pub_id pub_name city state ----- -------------- --------- ----- 0736 New Age Books Boston WA 0877 Binnet & Hardley Washington DC 1389 Algodata Infosystems Berkeley CA CHAPTER 2 Queries: Selecting Data from a Table Transact-SQL User’s Guide 45 (3 rows affected) If you listed all the column names in the table in order after the select keyword, you would get exactly the same results: select pub_id, pub_name, city, state from publishers You can also use “*” more than once in a query: select *, * from publishers This query displays each column name and each piece of column data twice. Like a column name, you can qualify an asterisk with a table name. For example: select publishers.* from publishers However, because select * finds all the columns currently in a table, changes in the structure of a table such as adding, removing, or renaming columns automatically modify the results of select *. Listing columns individually gives you more precise control over the results. Choosing specific columns To select only specific columns in a table, use: select column_name[, column_name]... from table_name Separate column names with commas, for example: select au_lname, au_fname from authors Rearranging the order of columns The order in which you list the column names in the select clause determines the order in which the columns display. The examples that follow show how to specify column order, displaying publisher names and identification numbers from all three rows in the publishers table. The first example prints pub_id first, followed by pub_name; the second reverses that order. The information is the same but the organization changes. Choosing columns: the select clause 46 Adaptive Server Enterprise select pub_id, pub_name from publishers pub_id pub_name ----- --------------- 0736 New Age Books 0877 Binnet & Hardley 1389 Algodata Infosystems (3 rows affected) select pub_name, pub_id from publishers pub_name pub_id --------------------- ------ New Age Books 0736 Binnet & Hardley 0877 Algodata Infosystems 1389 (3 rows affected) Renaming columns in query results When query results display, the default heading for each column is the name given to it when it was created. You can rename a column heading for display purposes by using one of the following instead of only the column name in a select list. column_heading = column_name or: column_name column_heading or: column_name as column_heading This provides a substitute name for the column. For example, to change pub_name to “Publisher” in the previous query, type any of the following statements: select Publisher = pub_name, pub_id from publishers select pub_name Publisher, pub_id from publishers select pub_name as Publisher, pub_id from publishers The results of these statements look like this: CHAPTER 2 Queries: Selecting Data from a Table Transact-SQL User’s Guide 47 Publisher pub_id ---------------------- ------ New Age Books 0736 Binnet & Hardley 0877 Algodata Infosystems 1389 (3 rows affected) Expressions The select statement can also include one or more expressions, which allow you to manipulate the data retrieved. select expression [, expression]... from table_list An expression is any combination of constants, column names, functions, subqueries, or case expressions, connected by arithmetic or bitwise operators and parentheses. If any table or column name in the list does not conform to the rules for valid identifiers, set the quoted_identifier option on and enclose the identifier in double quotes. Quoted strings in column headings You can include any characters—even blanks—in a column heading if you enclose the entire heading in quotation marks. You do not need to set the quoted_identifier option on. If the column heading is not enclosed in quotation marks, it must conform to the rules for identifiers. Both of the following queries produce the same result: select "Publisher’s Name" = pub_name from publishers select pub_name "Publisher’s Name" from publishers Publisher’s Name ---------------- New Age Books Binnet & Hardley Algodata Infosystems (3 rows affected)Choosing columns: the select clause 48 Adaptive Server Enterprise In addition, you can use Transact-SQL reserved words in quoted column headings. For example, the following query, using the reserved word sum as a column heading, is valid: select "sum" = sum(total_sales) from titles Quoted column headings cannot be more than 30 bytes long. Note Before using quotes around a column name in a create table, alter table, select into, or create view statement, you must set quoted_identifier on. Character strings in query results The select statements you have seen so far produce results showing data in the database. You can also write queries so that the results contain strings of characters. Enclose the string you want to include in single or double quotation marks and separate it from other elements in the select list with a comma. Use double quotation marks if there is an apostrophe in the string—otherwise, the apostrophe is interpreted as a single quotation mark. Here is a query with a character string: select "The publisher’s name is", Publisher = pub_name from publishers Publisher ------------------------ -------------------- The publisher’s name is New Age Books The publisher’s name is Binnet & Hardley The publisher’s name is Algodata Infosystems (3 rows affected) Computed values in the select list You can perform computations with data from numeric columns or on numeric constants in a select list. CHAPTER 2 Queries: Selecting Data from a Table Transact-SQL User’s Guide 49 Bitwise operators The bitwise operators are a Transact-SQL extension that you can use with integers. These operators convert each integer operand into its binary representation, then evaluates the operands column by column. A value of 1 corresponds to true; a value of 0 corresponds to false. Table 2-1 shows the bitwise operators. Table 2-1: Bitwise operators For more information on bitwise operators, see the Reference Manual. Arithmetic operators Table 2-2 shows the available arithmetic operators. Table 2-2: Arithmetic operators With the exception of the modulo operator, you can use any arithmetic operator on any numeric column (int, smallint, tinyint, numeric, decimal, float, or money) A modulo, which can be used on all numeric columns except money, finds the integer remainder after a division involving two whole numbers. For example, 21 % 11 = 10 because 21 divided by 11 equals 1, with a remainder of 10. You can perform certain arithmetic operations on date/time columns using the date functions. See Chapter 11, “Using the Built-In Functions in Queries,” for information. You can use all of these operators in the select list with column names and numeric constants in any combination. For example, to see what a projected sales increase of 100 percent for all the books in the titles table looks like, enter: select title_id, total_sales, total_sales * 2 from titles Operator Meaning & Bitwise and (two operands) | Bitwise or (two operands) ^ Bitwise exclusive or (two operands) ~ Bitwise not (one operand) Operator Operation + Addition - Subtraction / Division * Multiplication % ModuloChoosing columns: the select clause 50 Adaptive Server Enterprise Here are the results: title_id total_sales -------- ----------- --------- BU1032 4095 8190 BU1111 3876 7752 BU2075 18722 37444 BU7832 4095 8190 MC2222 2032 4064 MC3021 22246 44492 MC3026 NULL NULL PC1035 8780 17560 PC8888 4095 8190 PC9999 NULL NULL PS1372 375 750 PS2091 2045 4090 PS2106 111 222 PS3333 4072 8144 PS7777 3336 6672 TC3218 375 750 TC4203 15096 30192 TC7777 4095 8190 (18 rows affected) Notice the null values in the total_sales column and the computed column. Null values have no explicitly assigned values. When you perform any arithmetic operation on a null value, the result is NULL. You can give the computed column a heading, “proj_sales” for example, by entering: select title_id, total_sales, proj_sales = total_sales * 2 from titles title_id total_sales proj_sales --------- ----------- ----------- BU1032 4095 8190 .... Try adding character strings such as “Current sales =” and “Projected sales are” to the select statement. The column from which the computed column is generated does not have to appear in the select list. The total_sales column, for example, is shown in these sample queries only for comparison of its values with the values from the total_sales * 2 column. To see only the computed values, enter: select title_id, total_sales * 2 from titles CHAPTER 2 Queries: Selecting Data from a Table Transact-SQL User’s Guide 51 Arithmetic operators also work directly with the data values in specified columns, when no constants are involved. For example: select title_id, total_sales * price from titles title_id -------- ---------- BU1032 81,859.05 BU1111 46,318.20 BU2075 55,978.78 BU7832 81,859.05 MC2222 40,619.68 MC3021 66,515.54 MC3026 NULL PC1035 201,501.00 PC8888 81,900.00 PC9999 NULL PS1372 8,096.25 PS2091 22,392.75 PS2106 777.00 PS3333 81,399.28 PS7777 26,654.64 TC3218 7,856.25 TC4203 180,397.20 TC7777 61,384.05 (18 rows affected) Computed columns can also come from more than one table. The joining and subqueries chapters in this manual include information on multitable queries. As an example of a join, this query multiplies the number of copies of a psychology book sold by an outlet (the qty column from the salesdetail table) by the price of the book (the price column from the titles table). select salesdetail.title_id, stor_id, qty * price from titles, salesdetail where titles.title_id = salesdetail.title_id and titles.title_id = "PS2106" title_id stor_id ---------------- ----------- ------ PS2106 8042 210.00 PS2106 8042 350.00 PS2106 8042 217.00 (3 rows affected) Choosing columns: the select clause 52 Adaptive Server Enterprise Arithmetic operator precedence When there is more than one arithmetic operator in an expression, multiplication, division, and modulo are calculated first, followed by subtraction and addition. If all arithmetic operators in an expression have the same level of precedence, the order of execution is left to right. Expressions in parentheses take precedence over all other operations. For example, the following select statement multiplies the total sales of a book by its price to calculate a total dollar amount, then subtracts from that one half of the author’s advance. select title_id, total_sales * price - advance / 2 from titles The product of total_sales and price is calculated first, because the operator is multiplication. Next, the advance is divided by 2, and the result is subtracted from total_sales * price. To avoid misunderstandings, use parentheses. The following query has the same meaning and gives the same results as the previous one, but it is easier to understand: select title_id,(total_sales * price) - (advance /2) from titles title_id -------- ---------- BU1032 79,359.05 BU1111 43,818.20 BU2075 50,916.28 BU7832 79,359.05 MC2222 40,619.68 MC3021 59,015.54 MC3026 NULL PC1035 198,001.00 PC8888 77,900.00 PC9999 NULL PS1372 4,596.25 PS2091 1,255.25 PS2106 -2,223.00 PS3333 80,399.28 PS7777 24,654.64 TC3218 4,356.25 TC4203 178,397.20 TC7777 57,384.05 (18 rows affected)CHAPTER 2 Queries: Selecting Data from a Table Transact-SQL User’s Guide 53 Use parentheses to change the order of execution; calculations inside parentheses are handled first. If parentheses are nested, the most deeply nested calculation has precedence. For example, the result and meaning of the preceding example is changed if you use parentheses to force evaluation of the subtraction before the division: select title_id, (total_sales * price - advance) /2 from titles title_id -------- ----------------------- BU1032 38,429.53 BU1111 20,659.10 BU2075 22,926.89 BU7832 38,429.53 MC2222 20,309.84 MC3021 25,757.77 MC3026 NULL PC1035 97,250.50 PC8888 36,950.00 PC9999 NULL PS1372 548.13 PS2091 10,058.88 PS2106 -2,611.50 PS3333 39,699.64 PS7777 11,327.32 TC3218 428.13 TC4203 88,198.60 TC7777 26,692.03 (18 rows affected) Selecting text and image values text and image values can be quite large. When a select list includes text and image values, the limit on the length of the data returned depends on the setting of the @@textsize global variable. The default setting for @@textsize depends on the software you use to access Adaptive Server; the default value is 32K for isql. To change the value, use the set command: set textsize 25Choosing columns: the select clause 54 Adaptive Server Enterprise With this setting of @@textsize, a select statement that includes a text column displays only the first 25 bytes of the data. Note When you select image data, the returned value includes the characters “0x”, which indicates that the data is hexadecimal. These two characters are counted as part of @@textsize. To reset @@textsize to the Adaptive Server default value, use: set textsize 0 The default display is the actual length of the data when its size is less than textsize. For more information about text and image datatypes, see Chapter 7, “Using and Creating Datatypes.” Using readtext The readtext command provides a way to retrieve text and image values if you want to retrieve only a selected portion of a column’s data. readtext requires the name of the table and column, the text pointer, a starting offset within the column, and the number of characters or bytes to retrieve. This example finds six characters in the copy column in the blurbs table: declare @val binary(16) select @val = textptr(copy) from blurbs where au_id = "648-92-1872" readtext blurbs.copy @val 2 6 using chars In the example, after the @val local variable has been declared, readtext displays characters 3 - 8 of the copy column, since the offset was 2. Instead of storing potentially large text and image data in the table, Adaptive Server stores it in a special structure. A text pointer (textptr) which points to the page where the data is actually stored is assigned. When you retrieve data using readtext, you actually retrieve textptr, which is a 16-byte varbinary string. To avoid this, declare a local variable to hold textptr, and then use the variable with readtext, as in the example above. See “Text functions used for text and image data” on page 389 for an advanced discussion of the readtext command.CHAPTER 2 Queries: Selecting Data from a Table Transact-SQL User’s Guide 55 Select list summary The select list can include * (all columns in create table order), a list of column names in any order, character strings, column headings, and expressions including arithmetic operators. You can also include aggregate functions, which are discussed in Chapter 3, “Using Aggregates, Grouping, and Sorting.” Here are some select lists to try with the tables in the pubs2 sample database: • select titles.* from titles • select Name = au_fname, Surname = au_lname from authors • select Sales = total_sales * price, ToAuthor = advance, ToPublisher = (total_sales * price) - advance from titles • select "Social security #", au_id from authors • select this_year = advance, next_year = advance + advance/10, third_year = advance/2, "for book title #", title_id from titles • select "Total income is", Revenue = price * total_sales, "for", Book# = title_id from titles Eliminating duplicate query results with distinct The optional distinct keyword eliminates duplicate rows from the default results of a select statement. For compatibility with other implementations of SQL, Adaptive Server syntax allows the use of all to explicitly ask for all rows. The default for select statements is all. If you do not specify distinct, you will get, by default, all rows including duplicates. For example, here is the result of searching for all the author identification codes in the titleauthor table without distinct:Eliminating duplicate query results with distinct 56 Adaptive Server Enterprise select au_id from titleauthor au_id ----------- 172-32-1176 213-46-8915 213-46-8915 238-95-7766 267-41-2394 267-41-2394 274-80-9391 409-56-7008 427-17-2319 472-27-2349 486-29-1786 486-29-1786 648-92-1872 672-71-3249 712-45-1867 722-51-5454 724-80-9391 724-80-9391 756-30-7391 807-91-6654 846-92-7186 899-46-2035 899-46-2035 998-72-3567 998-72-3567 (25 rows affected) There are some duplicate listings. Use distinct to eliminate them. select distinct au_id from titleauthor au_id ----------- 172-32-1176 213-46-8915 238-95-7766 267-41-2394 274-80-9391 409-56-7008 427-17-2319 472-27-2349 486-29-1786 CHAPTER 2 Queries: Selecting Data from a Table Transact-SQL User’s Guide 57 648-92-1872 672-71-3249 712-45-1867 722-51-5454 724-80-9391 756-30-7391 807-91-6654 846-92-7186 899-46-2035 998-72-3567 (19 rows affected) distinct treats multiple null values as duplicates. In other words, when distinct is included in a select statement, only one NULL is returned, no matter how many null values are encountered. When used with the order by clause, distinct can return multiple values. See “order by and group by used with select distinct” on page 105 for more information. Specifying tables: the from clause The from clause is required in every select statement involving data from tables or views. Use it to list all the tables and views containing columns included in the select list and in the where clause. If the from clause includes more than one table or view, separate them with commas. The maximum number of tables and views allowed in a query is 16. This includes tables listed in the from clause, base tables referenced by a view definition, any tables referenced in subqueries, a table being created with the into keyword, and any tables referenced as part of referential integrity constraints. The from syntax looks like this: select select_list [from [[database.]owner.] {table_name |view_name} [holdlock | noholdlock] [shared] [, [[database.]owner.] {table_name | view_name} [holdlock | noholdlock] [shared]]...] Selecting rows: the where clause 58 Adaptive Server Enterprise Table names can be between 1 and 30 bytes long. You can use a letter, @, #, or _ as the first character. The characters that follow can be digits, letters, or @, #, $, _, ¥, or £. Temporary table names must begin either with “#” (pound sign), if they are created outside tempdb, or with “tempdb..”. If you create a temporary table outside tempdb, its name must be less than 13 bytes, since Adaptive Server attaches an internal numeric suffix to the name to ensure that the name is unique. For more information, see Chapter 8, “Creating Databases and Tables.” The full naming syntax for tables and views is always permitted in the from clause: database.owner.table_name database.owner.view_name However, the full naming syntax is necessary only if there is some confusion about the name. You can give table names correlation names to save typing. Assign the correlation name in the from clause by giving the correlation name after the table name, like this: select p.pub_id, p.pub_name from publishers p All other references to that table (for example, in a where clause) must also use the correlation name. Correlation names cannot begin with a numeral. Selecting rows: the where clause The where clause in a select statement specifies the search conditions that determine which rows are retrieved. The general format is: select select_list from table_list where search_conditions Search conditions, or qualifications, in the where clause include: • Comparison operators (=, <, >, and so on) where advance * 2 > total_sales * price • Ranges (between and not between) where total_sales between 4095 and 12000 CHAPTER 2 Queries: Selecting Data from a Table Transact-SQL User’s Guide 59 • Lists (in, not in) where state in ("CA", "IN", "MD") • Character matches (like and not like) where phone not like "415%" • Unknown values (is null and is not null) where advance is null • Combinations of search conditions (and, or) where advance < 5000 or total_sales between 2000 and 2500 The where keyword can also introduce: • Join conditions (see Chapter 6, “Joins: Retrieving Data from Several Tables”) • Subqueries (see Chapter 4, “Subqueries: Using Queries Within Other Queries”) Note The only where condition that you can use on text columns is like (or not like). For more information on search conditions, see the “where Clause” section in the Reference Manual. Comparison operators Transact-SQL uses these comparison operators: Selecting rows: the where clause 60 Adaptive Server Enterprise Table 2-3: Comparison operators The operators are used in this syntax: where expression comparison_operator expression An expression is a constant, column name, function, subquery, case expression, or any combination of these, connected by arithmetic or bitwise operators. In comparing character data, < means earlier in the sort order and > means later in the sort order. Use the sp_helpsort to display the sort order for your Adaptive Server. Trailing blanks are ignored for the purposes of comparison. For example, “Dirk” is the same as “Dirk ”. In comparing dates, < means earlier than and > means later than. Put apostrophes or quotation marks around all char, nchar, unichar, varchar, nvarchar, univarchar, text, and date/time data. For more information on entering date and time data, see Chapter 9, “Adding, Changing, and Deleting Data.” Here are some sample select statements that use comparison operators: select * from titleauthor where royaltyper < 50 select authors.au_lname, authors.au_fname from authors where au_lname > "McBadden" select au_id, phone from authors where phone != "415 658-9932" select title_id, newprice = price * $1.15 from pubs2..titles where advance > 5000 Operator Meaning = Equal to > Greater than < Less than >= Greater than or equal to <= Less than or equal to <> Not equal to != Not equal to (Transact-SQL extension) !> Not greater than (Transact-SQL extension) !< Not less than (Transact-SQL extension) CHAPTER 2 Queries: Selecting Data from a Table Transact-SQL User’s Guide 61 not negates an expression. Either of the following two queries finds all business and psychology books that have advances of less than $5500. Note the difference in position between the negative logical operator (not) and the negative comparison operator (!>). select title_id, type, advance from titles where (type = "business" or type = "psychology") and not advance >5500 select title_id, type, advance from titles where (type = "business" or type = "psychology") and advance !>5500 title_id type advance -------- ------------ -------- BU1032 business 5,000.00 BU1111 business 5,000.00 BU7832 business 5,000.00 PS2091 psychology 2,275.00 PS3333 psychology 2,000.00 PS7777 psychology 4,000.00 (6 rows affected) Ranges (between and not between) Use the between keyword to specify an inclusive range. For example, to find all the books with sales between and including 4095 and 12,000, you can write this query: select title_id, total_sales from titles where total_sales between 4095 and 12000 title_id total_sales ------ ----------- BU1032 4095 BU7832 4095 PC1035 8780 PC8888 4095 TC7777 4095 (5 rows affected) You can specify an exclusive range with the greater than (>) and less than (<) operators:Selecting rows: the where clause 62 Adaptive Server Enterprise select title_id, total_sales from titles where total_sales > 4095 and total_sales < 12000 title_id total_sales ------ ----------- PC1035 8780 (1 row affected) not between finds all rows outside the specified range. To find all the books with sales outside the $4095 to $12,000 range, type: select title_id, total_sales from titles where total_sales not between 4095 and 12000 title_id total_sales -------- ----------- BU1111 3876 BU2075 18722 MC2222 2032 MC3021 22246 PS1372 375 PS2091 2045 PS2106 111 PS3333 4072 PS7777 3336 TC3218 375 TC4203 15096 (11 rows affected) Lists (in and not in) The in keyword allows you to select values that match any one of a list of values. The expression can be a constant or a column name, and the values list can be a set of constants or a subquery. For example, to list the names and states of all authors who live in California, Indiana, or Maryland, you can use: select au_lname, state from authors where state = "CA" or state = "IN" or state = "MD"CHAPTER 2 Queries: Selecting Data from a Table Transact-SQL User’s Guide 63 Or, to get the same results with less typing, use in. Separate items following the in keyword by commas and enclose them in parentheses. Put single or double quotes around char, varchar, unichar, univarchar and datatime values. For example: select au_lname, state from authors where state in ("CA", "IN", "MD") This is what results from either query: au_lname state ----------- ----- White CA Green CA Carson CA O’Leary CA Straight CA Bennet CA Dull CA Gringlesby CA Locksley CA Yokomoto CA DeFrance IN Stringer CA MacFeather CA Karsen CA Panteley MD Hunter CA McBadden CA (17 rows affected) Perhaps the most important use for the in keyword is in nested queries, also called subqueries. For a full discussion of subqueries, see Chapter 4, “Subqueries: Using Queries Within Other Queries.” The following example gives an idea of what you can do with nested queries and the in keyword. Suppose you want to know the names of the authors who receive less than 50 percent of the total royalties on the books they co-author. The authors table gives author names and the titleauthor table gives royalty information. By putting the two tables together using in, but without listing the two tables in the same from clause, you can extract the information you need. The following query: • Searches the titleauthor table for all au_ids of authors making less than 50 percent of the royalty on any one book. Selecting rows: the where clause 64 Adaptive Server Enterprise • Selects from the authors table all the author names with au_ids that match the results from the titleauthor query. The results show that several authors fall into the less than 50 percent category. select au_lname, au_fname from authors where au_id in (select au_id from titleauthor where royaltyper <50) au_lname au_fname -------------- ------------ Green Marjorie O’Leary Michael Gringlesby Burt Yokomoto Akiko MacFeather Stearns Ringer Anne (6 rows affected) not in finds the authors that do not match the items in the list. The following query finds the names of authors who do not make less than 50 percent of the royalties on at least one book. select au_lname, au_fname from authors where au_id not in (select au_id from titleauthor where royaltyper <50) au_lname au_fname --------------- ------------ White Johnson Carson Cheryl Straight Dick Smith Meander Bennet Abraham Dull Ann Locksley Chastity Greene Morningstar Blotchet-Halls Reginald del Castillo Innes DeFrance Michel Stringer Dirk Karsen Livia Panteley Sylvia CHAPTER 2 Queries: Selecting Data from a Table Transact-SQL User’s Guide 65 Hunter Sheryl McBadden Heather Ringer Albert Smith Gabriella (18 rows affected) Pattern matching You can include wildcard characters in the where clause to search for unknown characters or to group data according to common features. The sections below describe pattern matching using SQL and Transact-SQL. For more information on pattern matching, see the Reference Manual. Matching character strings: like The like keyword searches for a character string that matches a pattern. like is used with char, varchar, nchar, nvarchar, unichar, univarchar binary, varbinary, text, and date/time data. The syntax for like is: {where | having} [not] column_name [not] like "match_string" match_string can include the symbols in Table 2-4:Pattern matching 66 Adaptive Server Enterprise Table 2-4: Special symbols for matching character strings You can match the column data to constants, variables, or other columns that contain the wildcard characters shown in Table 2-4. When using constants, enclose the match strings and character strings in quotation marks. For example, using like with the data in the authors table: • like “Mc%” searches for every name that begins with ‘‘Mc’’ (McBadden). • like “%inger” searches for every name that ends with ‘‘inger’’ (Ringer, Stringer). • like “%en%” searches for every name containing ‘‘en’’ (Bennet, Green, McBadden). • like “_heryl” searches for every six-letter name ending with ‘‘heryl’’ (Cheryl). • like “[CK]ars[eo]n” searches for ‘‘Carsen,’’ ‘‘Karsen,’’ ‘‘Carson,’’ and ‘‘Karson’’ (Carson). • like “[M-Z]inger” searches for all names ending with ‘‘inger’’ that begin with any single letter from M to Z (Ringer). • like “M[^c]%” searches for all names beginning with ‘‘M’’ that do not have ‘‘c’’ as the second letter. Symbols Meaning % Matches any string of zero or more characters. _ Matches a single character. [specifier] Brackets enclose ranges or sets, such as [a–f] or [abcdef]. specifier can take two forms: • rangespec1-rangespec2: rangespec1 indicates the start of a range of characters. - is a special character, indicating a range. rangespec2 indicates the end of a range of characters. • set: can be composed of any discrete set of values, in any order, such as [a2bR].The range [a–f], and the sets [abcdef] and [fcbdae] return the same set of values. Specifiers are case-sensitive. [^specifier] A caret (^) preceding a specifier indicates non-inclusion. [^a– f] means “not in the range a–f”; [^a2bR] means “not a, 2, b, or R.”CHAPTER 2 Queries: Selecting Data from a Table Transact-SQL User’s Guide 67 This query finds all the phone numbers in the authors table that have an area code of 415: select phone from authors where phone like "415%" The only where condition you can use on text columns is like. This query finds all the rows in the blurbs table where the copy column includes the word “computer”: select * from blurbs where copy like "%computer%" Adaptive Server interprets wildcard characters used without like as literals rather than as a pattern; they represent exactly their own values. The following query attempts to find any phone numbers that consist of the four characters “415%” only. It does not find phone numbers that start with 415. select phone from authors where phone = "415%" When you use like with date and time values, Adaptive Server converts the dates to the standard date/time format, and then to varchar or univarchar. Since the standard storage format does not include seconds or milliseconds, you cannot search for seconds or milliseconds with like and a pattern. It is a good idea to use like when you search for date and time values, since these datatype entries may contain a variety of date parts. For example, if you insert the value “9:20” and the current date into a column named arrival_time, this query will not find the value, because Adaptive Server converts the entry into “Jan 1 1900 9:20AM”: where arrival_time = "9:20" However, the clause below finds the 9:20 value: where arrival_time like "%9:20%" You can also use the date and time datatypes for like transactions. Using not like You can use the same wildcard characters with not like, that you can use with like. For example, to find all the phone numbers in the authors table that do not have 415 as the area code, you can use either of these queries: select phone Pattern matching 68 Adaptive Server Enterprise from authors where phone not like "415%" select phone from authors where not phone like "415%" not like and ^ may give different results You cannot always duplicate not like patterns with like and the negative wildcard character [^]. Match strings with negative wildcard characters are evaluated in steps, one character at a time. If the match fails at any point in the evaluation, it is eliminated. For example, this query finds the system tables in a database whose names begin with “sys”: select name from sysobjects where name like "sys%" If you have a total of 32 objects and like finds 13 names that match the pattern, not like will find the 19 objects that do not match the pattern. where name not like "sys%" A pattern such as the following may not produce the same results: like [^s][^y][^s]% Instead of 19, you might get only 14, with all the names that begin with “s” or have “y” as the second letter or have “s” as the third letter eliminated from the results, as well as the system table names. Using wildcard characters as literal characters You can search for wildcard characters by escaping them and searching for them as literals. There are two ways to use the wildcard characters as literals in a like match string: square brackets and the escape clause. The match string can also be a variable or a value in a table that contains a wildcard character. Square brackets (Transact-SQL extension) Use square brackets for the percent sign, the underscore, and right and left brackets. To search for a dash, rather than using it to specify a range, use the dash as the first character inside a set of brackets. CHAPTER 2 Queries: Selecting Data from a Table Transact-SQL User’s Guide 69 Table 2-5: Using square brackets to search for wildcard characters escape clause (SQL-compliant) Use the escape clause to specify an escape character in the like clause. An escape character must be a single character string. Any character in the server’s default character set can be used. Table 2-6: Using the escape clause An escape character is valid only within its like clause and has no effect on other like clauses in the same statement. The only characters that are valid following an escape character are the wildcard characters ( _ , % , [ , ] , and [^] ), and the escape character itself. The escape character affects only the character following it. If a pattern contains two literal occurrences of a character that happens to be an escape character, the string must contain four consecutive escape characters (see the last example in Table 2-6). Otherwise, Adaptive Server raises a SQLSTATE error condition and returns an error message. Specifying more than one escape character raises a SQLSTATE error condition, and Adaptive Server returns an error message: like "%XX_%" escape "XX" like "%XX%X_%" escape "XX" like clause Searches for like "5%" 5 followed by any string of 0 or more characters like "5[%]" 5% like "_n" an, in, on, and so forth like "[_]n" _n like "[a-cdf]" a, b, c, d, or f like "[-acdf]" -, a, c, d, or f like "[ [ ]" [ like "[ ] ]" ] like clause Searches for like "5@%" escape "@" 5% like "*_n" escape "*" _n like "%80@%%" escape "@" string containing 80% like "*_sql**%" escape "*" string containing _sql* like "%#####_#%%" escape "#" string containing ##_%Pattern matching 70 Adaptive Server Enterprise Interaction of wildcard characters and square brackets An escape character retains its special meaning within square brackets, unlike the wildcard characters. Do not use existing wildcard characters as escape characters in the escape clause, for these reasons: • If you specify “_” or “%” as an escape character, it loses its special meaning within that like clause and acts only as an escape character. • If you specify “[“or “]” as an escape character, the Transact-SQL meaning of the bracket is disabled within that like clause. • If you specify “-” or “^” as an escape character, it loses the special meaning that it normally has within square brackets and acts only as an escape character. Trailing blanks and % Adaptive Server truncates trailing blanks following “%” in a like clause to a single trailing blank. like ‘‘% ’’ (percent sign followed by 2 spaces) matches ‘‘X ‘’ (one space); ‘‘X ’’ (two spaces); ‘‘X ’’ (three spaces), or any number of trailing spaces. Using wildcard characters in columns You can use wildcard characters for columns and column names. You might want to create a table called special_discounts in the pubs2 database to run a price projection for a special sale: create table special_discounts id_type char(3), discount int) insert into special_discounts values("BU%", 10) ... The table should contain the following data: id_type discount ------- ----------- BU% 10 PS% 12 MC% 15 The following query uses wildcard characters in id_type in the where clause: select title_id, discount, price, price - (price*discount/100) CHAPTER 2 Queries: Selecting Data from a Table Transact-SQL User’s Guide 71 from special_discounts, titles where title_id like id_type Here are the results of that query: title_id discount price -------- ----------- -------------- -------------- BU1032 10 19.99 17.99 BU1111 10 11.95 10.76 BU2075 10 2.99 2.69 BU7832 10 19.99 17.99 PS1372 12 21.59 19.00 PS2091 12 10.95 9.64 PS2106 12 7.00 6.16 PS3333 12 19.99 17.59 PS7777 12 7.99 7.03 MC2222 15 19.99 16.99 MC3021 15 2.99 2.54 MC3026 15 NULL NULL (12 rows affected) This permits sophisticated pattern matching without having to construct a series of or clauses. Character strings and quotation marks When you enter or search for character and date data (char, nchar, unichar, varchar, nvarchar, univarchar, datetime, smalldatetime, date and time datatypes), you must enclose it in single or double quotation marks. See Chapter 1, “SQL Building Blocks” for more information on character data and Chapter 7, “Using and Creating Datatypes” for more information on date/time datatypes. “Unknown” values: NULL A NULL in a column means no entry has been made in that column. A data value for the column is “unknown” or “not available.” NULL is not synonymous with “zero” or “blank”. Rather, null values allow you to distinguish between a deliberate entry of zero for numeric columns (or blank for character columns) and a non-entry, which is NULL for both numeric and character columns. Pattern matching 72 Adaptive Server Enterprise NULL can be entered in a column where null values are permitted in two ways: • If you do not enter any data, Adaptive Server automatically enters “NULL”. • Users can explicitly enter the word “NULL” or “null” without quotation marks. If you type the word ‘‘NULL’’ in a character column and include quotation marks, it is treated as data, rather than a null value. Query results display the word NULL. For example, the advance column of the titles table allows null values. By inspecting the data in that column you can tell whether a book had no advance payment by agreement (the row MC2222 has zero in the advance column) or whether the advance amount was not known when the data was entered (the row MC3026 has NULL in the advance column). select title_id, type, advance from titles where pub_id = "0877" title_id type advance -------- ---------- --------- MC2222 mod_cook 0.00 MC3021 mod_cook 15,000.00 MC3026 UNDECIDED NULL PS1372 psychology 7,000.00 TC3218 trad_cook 7,000.00 TC4203 trad_cook 4,000.00 TC7777 trad_cook 8,000.00 (7 rows affected) Testing a column for null values Use is null in where, if, and while clauses (discussed in Chapter 14, “Using Batches and Control-of-Flow Language”) to compare column values to NULL and to select them or perform a particular action based on the results of the comparison. Only columns that return a value of TRUE are selected or result in the specified action; those that return FALSE or UNKNOWN do not. The following example selects only rows for which advance is less than $5000 or NULL: select title_id, advance from titles where advance < $5000 or advance is nullCHAPTER 2 Queries: Selecting Data from a Table Transact-SQL User’s Guide 73 Adaptive Server treats null values in different ways, depending on the operators that you use and the type of values you are comparing. In general, the result of comparing null values is UNKNOWN, since it is impossible to determine whether NULL is equal (or not equal) to a given value or to another NULL. The following cases return TRUE when expression is any column, variable or literal, or combination of these, which evaluates as NULL: • expression is null • expression = null • expression = @x where @x is a variable or parameter containing NULL. This exception facilitates writing stored procedures with null default parameters. • expression != n where n is a literal not containing NULL and expression evaluates to NULL. The negative versions of these expressions return TRUE when the expression does not evaluate to NULL: • expression is not null • expression != null • expression != @x When the keywords like and not like are used instead of the operators = and !=, the opposite occurs. This comparison returns TRUE: • expression not like null While this comparison returns FALSE: • expression like null Note that the far right side of these expressions is a literal null, or a variable or parameter containing NULL. If the far right side of the comparison is an expression (such as @nullvar + 1), the entire expression evaluates to NULL. Null column values do not join with other null column values. Comparing null column values to other null column values in a where clause always returns UNKNOWN, regardless of the comparison operator, and the rows are not included in the results. For example, this query returns no result rows where column1 contains NULL in both tables (although it may return other rows): select column1 from table1, table2 where table1.column1 = table2.column1 These operators return results when used with a NULL: Pattern matching 74 Adaptive Server Enterprise • = returns all rows that contain NULL. • != or <> returns all rows that do not contain NULL. When set ansinull is “on” for SQL compliance, the = and != operators do not return results when used with a NULL. Regardless of the set ansinull option value, the following operators never return values when used with a NULL: <, <=, !<, >, >=, !>. Adaptive Server can determine that a column value is NULL. Thus, this will be considered true: column1 = NULL However, the following comparisons can never be determined, since NULL means “having an unknown value”: where column1 > null There is no reason to assume that two unknown values are the same. This logic also applies when you use two column names in a where clause, that is, when you join two tables. A clause like “where column1 = column2” does not return rows where the columns contain null values. You can also find null values or non-null values with this pattern: where column_name is [not] null For example: where advance < $5000 or advance is null Some of the rows in the titles table contain incomplete data. For example, a book called The Psychology of Computer Cooking (title_id = MC3026) has been proposed and its title, title identification number, and probable publisher have been entered. However, since the author has no contract yet and details are still up in the air, null values appear in the price, advance, royalty, total_sales, and notes columns. Because null values do not match anything in a comparison, a query for all the title identification numbers and advances for books with advances of less than $5000 will not find The Psychology of Computer Cooking. select title_id, advance from titles where advance < $5000 title_id advance -------- ---------- MC2222 0.00 PS2091 2,275.00 PS3333 2,000.00 PS7777 4,000.00 CHAPTER 2 Queries: Selecting Data from a Table Transact-SQL User’s Guide 75 TC4203 4,000.00 (5 rows affected) Here is a query for books with an advance of less than $5000 or a null value in the advance column: select title_id, advance from titles where advance < $5000 or advance is null title_id advance -------- ---------- MC2222 0.00 MC3026 NULL PC9999 NULL PS2091 2,275.00 PS3333 2,000.00 PS7777 4,000.00 TC4203 4,000.00 (7 rows affected) See Chapter 8, “Creating Databases and Tables,” for information on NULL in the create table statement and for information on the relationship between NULL and defaults. See Chapter 9, “Adding, Changing, and Deleting Data,” for information on inserting null values into a table. Difference between FALSE and UNKNOWN There is an important logical difference between FALSE and UNKNOWN: the opposite of false (“not false”) is true, while the opposite of UNKNOWN is still UNKNOWN. For example, “1 = 2” evaluates to false and its opposite, “1 != 2”, evaluates to true. But “not unknown” is still unknown. If null values are included in a comparison, you cannot negate the expression to get the opposite set of rows or the opposite truth value. Substituting a value for NULLs Use the isnull built-in function to substitute a particular value for nulls. The substitution is made only for display purposes; actual column values are not affected. The syntax is: isnull(expression, value) Pattern matching 76 Adaptive Server Enterprise For example, use the following statement to select all the rows from titles, and display all the null values in column notes with the value unknown. select isnull(notes, "unknown") from titles Expressions that evaluate to NULL An expression with an arithmetic or bitwise operator evaluates to NULL if any of the operands is null. For example, this evaluates to NULL if column1 is NULL: 1 + column1 Concatenating strings and NULL If you concatenate a string and NULL, the expression evaluates to the string. For example: select "abc" + NULL + "def" ----- abcdef System-generated NULLs In Transact-SQL, system-generated NULLs, such as those that result from a system function like convert, behave differently than user-assigned NULLs. For example, in the following statement, a not equals comparison of the userprovided NULL and 1 returns TRUE: if (1 != NULL) print "yes" else print "no" yes The same comparison with a system-generated NULL returns UNKNOWN: if (1 != convert(integer, NULL)) print "yes" else print "no" no For more consistent behavior, set ansinull on. Then both system-generated and user-provided NULLs cause the comparison to return UNKNOWN.CHAPTER 2 Queries: Selecting Data from a Table Transact-SQL User’s Guide 77 Connecting conditions with logical operators The logical operators and, or, and not are used to connect search conditions in where clauses. The syntax is: {where | having} [not] column_name join_operator column_name where join_operator is a comparison operator and column_name is the column used in the comparison. Qualify the name of the column if there is any ambiguity. and joins two or more conditions and returns results only when all of the conditions are true. For example, the following query finds only the rows in which the author’s last name is Ringer and the author’s first name is Anne. It does not find the row for Albert Ringer. select * from authors where au_lname = "Ringer" and au_fname = "Anne" or also connects two or more conditions, but it returns results when any of the conditions is true. The following query searches for rows containing Anne or Ann in the au_fname column. select * from authors where au_fname = "Anne" or au_fname = "Ann" You can specify as many as 252 and and or conditions. not negates the expression that follows it. The following query selects all the authors who do not live in California: select * from authors where not state = "CA" When more than one logical operator is used in a statement, and operators are normally evaluated before or operators. You can change the order of execution with parentheses. For example: select * from authors where (city = "Oakland" or city = "Berkeley") and state = "CA" Pattern matching 78 Adaptive Server Enterprise Logical operator precedence Arithmetic and bitwise operators are handled before logical operators. When more than one logical operator is used in a statement, not is evaluated first, then and, and finally or. See “Bitwise operators” on page 14 for more information. For example, the following query finds all the business books in the titles table, no matter what their advances are, as well as all psychology books that have an advance of more than $5500. The advance condition pertains only to psychology books because the and is handled before the or. select title_id, type, advance from titles where type = "business" or type = "psychology" and advance > 5500 title_id type advance -------- ---------- ---------- BU1032 business 5,000.00 BU1111 business 5,000.00 BU2075 business 10,125.00 BU7832 business 5,000.00 PS1372 psychology 7,000.00 PS2106 psychology 6,000.00 (6 rows affected) You can change the meaning of the query by adding parentheses to force evaluation of the or first. This query finds all business and psychology books that have advances of more than $5500: select title_id, type, advance from titles where (type = "business" or type = "psychology") and advance > 5500 title_id type advance -------- ---------- --------- BU2075 business 10,125.00 PS1372 psychology 7,000.00 PS2106 psychology 6,000.00 (3 rows affected) Transact-SQL User’s Guide 79 C H A P T E R 3 Using Aggregates, Grouping, and Sorting This chapter addresses the sum, avg, count, count(*), max, and min aggregate functions that enable you to summarize the data retrieved in a query. This chapter also discusses how to organize data into categories and subgroups using the group by, having, and order by clauses. Two TransactSQL extensions—the compute clause and the union operator, are also discussed. This chapter contains the following sections: If your Adaptive Server is not case sensitive, see group by and having Clauses and compute Clause in the Reference Manual for examples on how case sensitivity affects the data returned by these clauses. Using aggregate functions The aggregate functions are: sum, avg, count, min, max, and count(*). You can use aggregate functions to calculate and summarize data. For example, to find out how many books have been sold in the titles table of the pubs2 database, type: select sum(total_sales) from titles ------------- 97746 Topic Page Using aggregate functions 79 Organizing query results into groups: the group by clause 85 Selecting groups of data: the having clause 97 Sorting query results: the order by clause 103 Summarizing groups of data: the compute clause 106 Combining queries: the union operator 114Using aggregate functions 80 Adaptive Server Enterprise (1 row affected) Note that there is no column heading for the aggregate column in the example. An aggregate function take as an argument the column name on whose values it will operate. You can apply aggregate functions to all the rows in a table, to a subset of the table specified by a where clause, or to one or more groups of rows in the table. From each set of rows to which an aggregate function is applied, Adaptive Server generates a single value. Here is the syntax of the aggregate function: aggregate_function ( [all | distinct] expression) Expression is usually a column name. However, it can also be a constant, a function, or any combination of column names, constants, and functions connected by arithmetic or bitwise operators. You can also use a case expression or subquery in an expression. For example, with this statement you can calculate the average price of all books if prices were doubled: select avg(price * 2) from titles ------------- 29.53 (1 row affected) You can use the optional keyword distinct with sum, avg, and count to eliminate duplicate values before the aggregate function is applied. all, which performs the operation on all rows, is the default. The syntax of the aggregate functions and the results they produce are shown in Table 3-1: Table 3-1: Syntax and results of aggregate functions Aggregate Function Result sum([all|distinct] expression) Total of the (distinct) values in the expression avg([all|distinct] expression) Average of the (distinct) values in the expression count([all|distinct] expression) Number of (distinct) non-null values in the expression count(*) Number of selected rows max(expression) Highest value in the expression min(expression) Lowest value in the expressionCHAPTER 3 Using Aggregates, Grouping, and Sorting Transact-SQL User’s Guide 81 You can use the aggregate functions in a select list, as shown in the previous example, or in the having clause. For information about the having clause, see “Selecting groups of data: the having clause” on page 97. You cannot use aggregate functions in a where clause, but most select statements with an aggregate function in the select list include a where clause that restricts the rows to which the aggregate is applied. In the examples given earlier in this section, each aggregate function produced a single summary value for the whole table. If a select statement includes a where clause, but not a group by clause (see “Organizing query results into groups: the group by clause” on page 85), an aggregate function produces a single value for the subset of rows, called a scalar aggregate. However, a select statement can also include a column in its select list (a Transact-SQL extension), that repeats the single value for each row in the result table. This query returns the average advance and the sum of sales for business books only, and has a column name preceding it called “advance and sales”: select “advance and sales”, avg(advance), sum(total_sales) from titles where type = "business" ----------------- ----------------- ----------- advance and sales 6,281.25 30788 (1 row affected) Aggregate functions and datatypes You can use the aggregate functions with any type of column, with the following exceptions: • You can use sum and avg with numeric columns only—int, smallint, tinyint, decimal, numeric, float, and money. • You cannot use min and max with bit datatypes. • You cannot use aggregate functions other than count(*) with text and image datatypes. For example, you can use min (minimum) to find the lowest value—the one closest to the beginning of the alphabet—in a character type column: select min(au_lname) Using aggregate functions 82 Adaptive Server Enterprise from authors -------------------------- Bennet (1 row affected) However, you cannot average the contents of a text column: select avg(au_lname) from authors -------------------------- Bennet (1 row affected) Msg 257, Level 16, State 1: Line 1: Implicit conversion from datatype ’VARCHAR’ to ’INT’ is not allowed. Use the CONVERT function to run this query. count vs. count (*) While count finds the number of non-null values in the expression, count(*) finds the total number of rows in a table. This statement finds the total number of books: select count(*) from titles ------------------ 18 (1 row affected) count(*) returns the number of rows in the specified table without eliminating duplicates. It counts each row, including those containing null values. Like other aggregate functions, you can combine count(*) with other aggregates in the select list, with where clauses, and so on: select count(*), avg(price) from titles where advance > 1000 ---------- --------- 15 14.42 (1 row affected) CHAPTER 3 Using Aggregates, Grouping, and Sorting Transact-SQL User’s Guide 83 Using aggregate functions with distinct You can use the optional keyword distinct only with sum, avg, and count. When you use distinct, Adaptive Server eliminates duplicate values before performing calculations. If you use distinct, you cannot include an arithmetic expression in the argument. The argument must use a column name only. distinct appears inside the parentheses and before the column name. For example, to find the number of different cities in which there are authors, enter: select count(distinct city) from authors ------------- 16 (1 row affected) For an accurate calculation of the average price of all business books, omit distinct. The following statement returns the average price of all business books: select avg(price) from titles where type = "business" ------------- 13.73 (1 row affected) However, if two or more books have the same price and you use distinct, the shared price is included only once in the calculation: select avg(distinct price) from titles where type = "business" ------------- 11.64 (1 row affected)Using aggregate functions 84 Adaptive Server Enterprise Null values and the aggregate functions Adaptive Server ignores any null values in the column on which the aggregate function is operating for the purposes of the function (except count(*), which includes them). If you have set ansinull to on, Adaptive Server returns an error message whenever a null value is ignored. For more information, see the set command in the Reference Manual. For example, the count of advances in the titles table is not the same as the count of title names, because of the null values in the advance column: select count(advance) from titles ------------- 16 (1 row affected) select count(title) from titles ------------- 18 (1 row affected) If all the values in a column are null, count returns 0. If no rows meet the conditions specified in the where clause, count returns 0. The other functions all return NULL. Here are examples: select count(distinct title) from titles where type = "poetry" ------------- 0 (1 row affected) select avg(advance) from titles where type = "poetry" ------------- NULL (1 row affected)CHAPTER 3 Using Aggregates, Grouping, and Sorting Transact-SQL User’s Guide 85 Organizing query results into groups: the group by clause The group by clause divides the output of a query into groups. You can group by one or more column names, or by the results of computed columns using numeric datatypes in an expression. When used with aggregates, group by retrieves the calculations in each subgroup, and may return multiple rows. The maximum number of columns or expressions you can use in a group by clause is 31. Note You cannot group by columns of text or image datatypes. While you can use group by without aggregates, such a construction has limited functionality and may produce confusing results. The following example groups the results by title type: select type, advance from titles group by type type advance ------------ --------- business 5,000.00 business 5,000.00 business 10,125.00 business 5,000.00 mod_cook 0.00 mod_cook 15,000.00 UNDECIDED NULL popular_comp 7,000.00 popular_comp 8,000.00 popular_comp NULL psychology 7,000.00 psychology 2,275.00 psychology 6,000.00 psychology 2,000.00 psychology 4,000.00 trad_cook 7,000.00 trad_cook 4,000.00 trad_cook 8,000.00 (18 rows affected) With an aggregate for the advance column, the query returns the sum for each group:Organizing query results into groups: the group by clause 86 Adaptive Server Enterprise select type, sum(advance) from titles group by type type ------------ ------------------------ UNDECIDED NULL business 25,125.00 mod_cook 15,000.00 popular_comp 15,000.00 psychology 21,275.00 trad_cook 19,000.00 (6 rows affected) The summary values in a group by clause using aggregates are called vector aggregates, as opposed to scalar aggregates, which result when only one row is returned (see “Using aggregate functions” on page 79). group by syntax The complete syntax of the select statement is repeated here so that you can see the group by clause in context: select [all | distinct] select_list [into [[database.]owner.]table_name] [from [[database.]owner.]{view_name | table_name [(index {index_name | table_name} [parallel [degree_of_parallelism]] [prefetch size ] [lru | mru])]} [holdlock | noholdlock] [shared] [,[[database.]owner.]{view_name | tablel_name [(index {index_name | table_name} [parallel [degree_of_parallelism]] [prefetch size] [lru | mru])]} [holdlock | noholdlock] [shared]]...] [where search_conditions] [group by [all] aggregate_free_expression [, aggregate_free_expression]...] [having search_conditions] [order by {[[[database.]owner.] {table_name. | view_name.}] column_name | select_list_number | expression} [asc | desc] [, {[[[database.]owner.]{table_name|view_name.}] column_name | select_list_number | expressionCHAPTER 3 Using Aggregates, Grouping, and Sorting Transact-SQL User’s Guide 87 [asc | desc]]...] [compute row_aggregate (column_name) [, row_aggregate(column_name)]... [by column_name [, column_name]...]] [for {read only | update [of column_name_list]}] [at isolation {read uncommitted | read committed | serializable}] [for browse] Remember that the order of the clauses in the select statement is significant. You can omit any of the optional clauses, but when you use them, they must appear in the order shown above. group by and SQL standards The SQL standards for group by are more restrictive than Sybase’s standard. The SQL standard requires that: • The columns in a select list must be in the group by expression or they must be arguments of aggregate functions. • A group by expression can only contain column names in the select list, but not those used only as arguments for vector aggregates. Several Transact-SQL extensions (described in the following sections) relax these restrictions, however the more complex result sets may be more difficult to understand. If you set the fipsflagger option as follows, you will receive a warning message stating that Transact-SQL extensions are used: set fipsflagger on For more information about the fipsflagger option, see the set command in the Reference Manual. Nesting groups with group by You can list more than one column in the group by clause to nest groups. Once the sets are established with group by, the aggregates are applied. This statement finds the average price and the sum of book sales, grouped first by publisher identification number and then by type: select pub_id, type, avg(price), sum(total_sales) from titles group by pub_id, type pub_id type ------ ------------ ------ ------- 0736 business 2.99 18,722 Organizing query results into groups: the group by clause 88 Adaptive Server Enterprise 0736 psychology 11.48 9,564 0877 UNDECIDED NULL NULL 0877 mod_cook 11.49 24,278 0877 psychology 21.59 375 0877 trad_cook 15.96 19,566 1389 business 17.31 12,066 1389 popular_comp 21.48 12,875 (8 rows affected) You can nest many groups within groups, up to the maximum of 16 columns or expressions specified with group by. Referencing other columns in queries using group by SQL standards state that the group by must contain items from the select list. However, Transact-SQL allows you to specify any valid column name in either the group by or select list, whether they employ aggregates or not. Through the following extensions, Sybase lifts restrictions on what you can include or omit in the select list of a query that includes group by. • The columns in the select list are not limited to the grouping columns and columns used with the vector aggregates. • The columns specified by group by are not limited to those non-aggregate columns in the select list. A vector aggregate must be accompanied by a group by clause. The SQL standards require that the non-aggregate columns in the select list match the group by columns. However, the first bulleted item described above allows you to specify additional, extended columns in the select list of the query. For example, many versions of SQL do not allow the inclusion of the extended title_id column in the select list, but it is legal in Transact-SQL: select type, title_id, avg(price), avg(advance) from titles group by type type title_id ------------ -------- ----- ------- business BU1032 13.73 6,281.25 business BU1111 13.73 6,281.25 business BU2075 13.73 6,281.25 business BU7832 13.73 6,281.25 mod_cook MC2222 11.49 7,500.00 CHAPTER 3 Using Aggregates, Grouping, and Sorting Transact-SQL User’s Guide 89 mod_cook MC3021 11.49 7,500.00 UNDECIDED MC3026 NULL NULL popular_comp PC1035 21.48 7,500.00 popular_comp PC8888 21.48 7,500.00 popular_comp PC9999 21.48 7,500.00 psychology PS1372 13.50 4,255.00 psychology PS2091 13.50 4,255.00 psychology PS2106 13.50 4,255.00 psychology PS3333 13.50 4,255.00 psychology PS7777 13.50 4,255.00 trad_cook TC3218 15.96 6,333.33 trad_cook TC4203 15.96 6,333.33 trad_cook TC7777 15.96 6,333.33 (18 rows affected) The above example still aggregates the price and advance columns based on the type column, but its results also display the title_id for the books included in each group. The second extension described above allows you to group columns that are not specified as columns in the select list of the query. These columns do not appear in the results, but the vector aggregates still compute their summary values. For example: select state, count(au_id) from authors group by state, city state ----- -------- CA 2 CA 1 CA 5 CA 5 CA 2 CA 1 CA 1 CA 1 CA 1 IN 1 KS 1 MD 1 MI 1 OR 1 TN 1 UT 2Organizing query results into groups: the group by clause 90 Adaptive Server Enterprise (16 rows affected) This example groups the vector aggregate results by both state and city, even though it does not display which city belongs to each group. Therefore, results are potentially misleading. You may think the following query should produce similar results to the previous query, since only the vector aggregate seems to tally the number of each city for each row: select state, count(au_id) from authors group by city However, its results are much different. By not using group by with both the state and city columns, the query tallies the number of each city, but it displays the tally for each row of that city in authors rather than grouping them into one result row per city. state ----- ----------- CA 1 CA 5 CA 2 CA 1 CA 5 KS 1 CA 2 CA 2 CA 1 CA 1 TN 1 OR 1 CA 1 MI 1 IN 1 CA 5 CA 5 CA 5 MD 1 CA 2 CA 1 UT 2 UT 2 (23 rows affected)CHAPTER 3 Using Aggregates, Grouping, and Sorting Transact-SQL User’s Guide 91 When you use the Transact-SQL extensions in complex queries that include the where clause or joins, the results may become even more difficult to understand. To avoid confusing or misleading results with group by, Sybase suggests that you use the fipsflagger option to identify queries that use TransactSQL extensions. See “group by and SQL standards” on page 87 for details. For more information about Transact-SQL extensions to group by and how they work, see the Reference Manual. Expressions and group by Another Transact-SQL extension allows you to group by an expression that does not include aggregate functions. For example: select avg(total_sales), total_sales * price from titles group by total_sales * price --------- ------------- NULL NULL 111 777.00 375 7,856.25 375 8,096.25 2045 22,392.75 3336 26,654.64 2032 40,619.68 3876 46,318.20 18722 55,978.78 4095 61,384.05 22246 66,515.54 4072 81,399.28 4095 81,859.05 4095 81,900.00 15096 180,397.20 8780 201,501.00 (16 rows affected) The expression “total_sales * price” is allowed. You cannot group by a column heading, also known as an alias, although you can still use one in your select list. This statement produces an error message: select Category = type, title_id, avg(price), avg(advance) from titles group by CategoryOrganizing query results into groups: the group by clause 92 Adaptive Server Enterprise The group by clause should be “group by type”, not “group by Category”. select Category = type, title_id, avg(price), avg(advance) from titles group by type Nesting aggregates with group by Another Transact-SQL extension allows you to nest a vector aggregate inside a scalar aggregate. For example, to find the average price of all types of books using a non-nested aggregate, enter: select avg(price) from titles group by type --------------- NULL 13.73 11.49 21.48 13.50 15.96 (6 rows affected) Nesting the average price inside the max function produces the highest average price of a group of books, grouped by type: select max(avg(price)) from titles group by type ------------- 21.48 (1 row affected) By definition, the group by clause applies to the innermost aggregate—in this case, avg.CHAPTER 3 Using Aggregates, Grouping, and Sorting Transact-SQL User’s Guide 93 Null values and group by If the grouping column contains a null value, that row becomes its own group in the results. If the grouping column contains more than one null value, the null values form a single group. Here is an example that uses group by and the advance column, which contains some null values: select advance, avg(price * 2) from titles group by advance advance ------------------ ----------------- NULL NULL 0.00 39.98 2000.00 39.98 2275.00 21.90 4000.00 19.94 5000.00 34.62 6000.00 14.00 7000.00 43.66 8000.00 34.99 10125.00 5.98 15000.00 5.98 (11 rows affected) If you are using the count(column_name) aggregate function, grouping by a column that contains null values will return a count of zero for the grouping row, since count(column_name) does not count null values. In most cases, you should use count(*) instead. This example groups and counts on the price column from the titles table, which contains null values, and shows count(*) for comparison: select price, count(price), count(*) from titles group by price price ------------- ----- ----- NULL 0 2 2.99 2 2 7.00 1 1 7.99 1 1 10.95 1 1 11.95 2 2 14.99 1 1 19.99 4 4 20.00 1 1 Organizing query results into groups: the group by clause 94 Adaptive Server Enterprise 20.95 1 1 21.59 1 1 22.95 1 1 (12 rows affected) where clause and group by You can use a where clause in a statement with group by. Rows that do not satisfy the conditions in the where clause are eliminated before any grouping is done. Here is an example: select type, avg(price) from titles where advance > 5000 group by type type ------------- -------- business 2.99 mod_cook 2.99 popular_comp 21.48 psychology 14.30 trad_cook 17.97 (5 rows affected) Only the rows with advances of more than $5000 are included in the groups that are used to produce the query results. However, the way that Adaptive Server handles extra columns in the select list and the where clause may seem contradictory. For example: select type, advance, avg(price) from titles where advance > 5000 group by type type advance ------------- --------- -------- business 5,000.00 2.99 business 5,000.00 2.99 business 10,125.00 2.99 business 5,000.00 2.99 mod_cook 0.00 2.99 mod_cook 15,000.00 2.99 popular_comp 7,000.00 21.48 popular_comp 8,000.00 21.48CHAPTER 3 Using Aggregates, Grouping, and Sorting Transact-SQL User’s Guide 95 popular_comp NULL 21.48 psychology 7,000.00 14.30 psychology 2,275.00 14.30 psychology 6,000.00 14.30 psychology 2,000.00 14.30 psychology 4,000.00 14.30 trad_cook 7,000.00 17.97 trad_cook 4,000.00 17.97 trad_cook 8,000.00 17.97 (17 rows affected) It only seems as if the query is ignoring the where clause when you look at the results for the advance (extended) column. Adaptive Server still computes the vector aggregate using only those rows that satisfy the where clause, but it also displays all rows for any extended columns that you include in the select list. To further restrict these rows from the results, you must use a having clause (described later in this chapter). group by and all The keyword all in the group by clause is a Transact-SQL enhancement. It is meaningful only if the select statement in which it is used also includes a where clause. If you use all, the query results include all the groups produced by the group by clause, even if some groups do not have any rows that meet the search conditions. Without all, a select statement that includes group by does not show groups for which no rows qualify. Here is an example: select type, avg(advance) from titles where advance > 1000 and advance < 10000 group by type type ------------ ------------------------ business 5,000.00 popular_comp 7,500.00 psychology 4,255.00 trad_cook 6,333.33 (4 rows affected) select type, avg(advance) Organizing query results into groups: the group by clause 96 Adaptive Server Enterprise from titles where advance > 1000 and advance < 10000 group by all type type ------------ ------------------------ UNDECIDED NULL business 5,000.00 mod_cook NULL popular_comp 7,500.00 psychology 4,255.00 trad_cook 6,333.33 (6 rows affected) The first statement produces groups only for those books that commanded advances of more than $1000 but less than $10,000. Since no modern cooking books have an advance within that range, there is no group in the results for the mod_cook type. The second statement produces groups for all types, including modern cooking and “UNDECIDED,” even though the modern cooking group does not include any rows that meet the qualification specified in the where clause. Adaptive Server returns a NULL result for all groups that lack qualifying rows. Using aggregates without group by By definition, scalar aggregates apply to all rows in a table, producing a single value for the whole table for each function. The Transact-SQL extension that allows you to include extended columns with vector aggregates also allows you to include extended columns with scalar aggregates. For example, look at the publishers table: pub_id pub_name city state ------ ------------------ -------------- ----- 0736 New Age Books Boston MA 0877 Binnet & Hardley Washington DC 1389 Algodata Infosystems Berkeley CA It contains three rows. The following query produces a three-row scalar aggregate based on each row of the table: select pub_id, count(pub_id) from publishers pub_id ---------- --------- 0736 3CHAPTER 3 Using Aggregates, Grouping, and Sorting Transact-SQL User’s Guide 97 0877 3 1389 3 (3 rows affected) Because Adaptive Server treats publishers as a single group, the scalar aggregate applies to the (single-group) table. The results display every row of the table for each column you include in the select list, in addition to the scalar aggregate. The where clause behaves the same way for scalar aggregates as with vector aggregates. The where clause restricts the columns included in the aggregate summary values, but it does not affect the rows that appear in the results for each extended column you specify in the select list. For example: select pub_id, count(pub_id) from publishers where pub_id < "1000" pub_id -------------- ----------- 0736 2 0877 2 1389 2 (3 rows affected) Like the other Transact-SQL extensions to group by, this extension provides results that may be difficult to understand, especially for queries on large tables or queries with multitable joins. Selecting groups of data: the having clause Use the having clause to display or reject rows defined by the group by clause. The having clause sets conditions for the group by clause in the same way where sets conditions for the select clause, except where cannot include aggregates, while having often does. This example is legal: select title_id from titles where title_id like "PS%" having avg(price) > $2.0 But this example is not: select title_idSelecting groups of data: the having clause 98 Adaptive Server Enterprise from titles where avg(price) > $20 having clauses can reference any of the items that appear in the select list. This statement is an example of a having clause with an aggregate function. It groups the rows in the titles table by type, but eliminates the groups that include only one book: select type from titles group by type having count(*) > 1 type ---------------- business mod_cook popular_comp psychology trad_cook (5 rows affected) Here is an example of a having clause without aggregates. It groups the titles table by type and displays only those types that start with the letter “p”: select type from titles group by type having type like "p%" type ------------ popular_comp psychology (2 rows affected) When you include more than one condition in the having clause, combine the conditions with and, or, or not. For example, to group the titles table by publisher, and to include only those publishers who have paid more than $15,000 in total advances, whose books average less than $18 in price, and whose identification numbers (pub_id) are greater than 0800, the statement is: select pub_id, sum(advance), avg(price) from titles group by pub_id having sum(advance) > 15000 and avg(price) < 18 and pub_id > "0800"CHAPTER 3 Using Aggregates, Grouping, and Sorting Transact-SQL User’s Guide 99 pub_id ------ ---------------- ---------------- 0877 41,000.00 15.41 (1 row affected) How the having, group by, and where clauses interact When you include the having, group by, and where clauses in a query, the sequence in which each clause affects the rows determines the final results: • The where clause excludes rows that do not meet its search conditions. • The group by clause collects the remaining rows into one group for each unique value in the group by expression. • Aggregate functions specified in the select list calculate summary values for each group. • The having clause excludes rows from the final results that do not meet its search conditions. The following query illustrates the use of where, group by, and having clauses in one select statement containing aggregates: select stor_id, title_id, sum(qty) from salesdetail where title_id like "PS%" group by stor_id, title_id having sum(qty) > 200 stor_id title_id ------- -------- ----------- 5023 PS1372 375 5023 PS2091 1,845 5023 PS3333 3,437 5023 PS7777 2,206 6380 PS7777 500 7067 PS3333 345 7067 PS7777 250 (7 rows affected) The query functioned in this order: 1 The where clause identified only rows with title_id beginning with “PS” (psychology books), Selecting groups of data: the having clause 100 Adaptive Server Enterprise 2 group by collected the rows by common stor_id and title_id, 3 The sum aggregate calculated the total number of books sold for each group, and 4 The having clause excluded the groups whose totals do not exceed 200 books from the final results. All of the previous having examples adhere to the SQL standards, which specify that columns in a having expression must have a single value, and must be in the select list or group by clause. However, the Transact-SQL extensions to having allow columns or expressions not in the select list and not in the group by clause. The following example determines the average price for each title type, but it excludes those types that do not have more than $10,000 in total sales, even though the sum aggregate does not appear in the results. select type, avg(price) from titles group by type having sum(total_sales) > 10000 type ------------ ---------- business 13.73 mod_cook 11.49 popular_comp 21.48 trad_cook 15.96 (4 rows affected) The extension behaves as if the column or expression were part of the select list but not part of the displayed results. If you include an non-aggregated column with having, but it is not part of the select list or the group by clause, the query produces results similar to the “extended” column extension described earlier in this chapter. For example: select type, avg(price) from titles group by type having total_sales > 4000 type ------------ ---------- business 13.73 business 13.73 business 13.73 mod_cook 11.49 popular_comp 21.48CHAPTER 3 Using Aggregates, Grouping, and Sorting Transact-SQL User’s Guide 101 popular_comp 21.48 psychology 13.50 trad_cook 15.96 trad_cook 15.96 (9 rows affected) Unlike an extended column, the total_sales column does not appear in the final results, yet the number of displayed rows for each type depends on the total_sales for each title. The query indicates that three business, one mod_cook, two popular_comp, one psychology, and two trad_cook, titles exceed $4000 in total sales. As mentioned earlier, the way Adaptive Server handles extended columns may seem as if the query is ignoring the where clause in the final results. To make the where conditions affect the results for the extended column, you should repeat the conditions in the having clause. For example: select type, advance, avg(price) from titles where advance > 5000 group by type having advance > 5000 type advance ------------- --------- -------- business 10,125.00 2.99 mod_cook 15,000.00 2.99 popular_comp 7,000.00 21.48 popular_comp 8,000.00 21.48 psychology 7,000.00 14.30 psychology 6,000.00 14.30 trad_cook 7,000.00 17.97 trad_cook 8,000.00 17.97 (8 rows affected) Using having without group by A query with a having clause should also have a group by clause. If you omit group by, all the rows not excluded by the where clause return as a single group. Because no grouping is done between the where and having clauses, they cannot act independently of each other. having acts like where because it affects the rows in a single group rather than groups, except the having clause can still use aggregates. Selecting groups of data: the having clause 102 Adaptive Server Enterprise This example uses the having clause in the following way: it averages the price, excludes from the results titles with advances greater than $4,000, and produces results where price is less than the average price: select title_id, advance, price from titles where advance < 4000 having price > avg(price) title_id advance price ------------- --------- -------- BU1032 5,000.00 19.99 BU7832 5,000.00 19.99 MC2222 0.00 19.99 PC1035 7,000.00 22.95 PC8888 8,000.00 20.00 PS1372 7,000.00 21.59 PS3333 2,000.00 19.99 TC3218 7,000.00 20.95 (8 rows affected) You can also use the having clause with the Transact-SQL extension that allows you to omit the group by clause from a query that includes an aggregate in its select list. These scalar aggregate functions calculate values for the table as a single group, not for groups within the table. In this example, the group by clause is omitted, which makes the aggregate function calculate a value for the whole table. The having clause excludes nonmatching rows from the result group. select pub_id, count(pub_id) from publishers having pub_id < "1000" pub_id ------ ---------------- 0736 3 0877 3 (2 rows affected)CHAPTER 3 Using Aggregates, Grouping, and Sorting Transact-SQL User’s Guide 103 Sorting query results: the order by clause The order by clause allows you to sort query results by one or more columns, up to 31. Each sort is either ascending (asc) or descending (desc). If neither is specified, asc is the default. The following query orders results by pub_id: select pub_id, type, title_id from titles order by pub_id pub_id type title_id ------ ------------ -------- 0736 business BU2075 0736 psychology PS2091 0736 psychology PS2106 0736 psychology PS3333 0736 psychology PS7777 0877 UNDECIDED MC3026 0877 mod_cook MC2222 0877 mod_cook MC3021 0877 psychology PS1372 0877 trad_cook TC3218 0877 trad_cook TC4203 0877 trad_cook TC7777 1389 business BU1032 1389 business BU1111 1389 business BU7832 1389 popular_comp PC1035 1389 popular_comp PC8888 1389 popular_comp PC9999 (18 rows affected) If you name more than one column in the order by clause, Adaptive Server nests the sorts. The following statement sorts the rows in the stores table first by stor_id in descending order, then by payterms (in ascending order, since desc is not specified), and finally by country (also ascending). Adaptive Server sorts null values first within any group. select stor_id, payterms, country from stores order by stor_id desc, payterms stor_id payterms country ------- ------------ ------------ 8042 Net 30 USA 7896 Net 60 USA 7131 Net 60 USA 7067 Net 30 USA Sorting query results: the order by clause 104 Adaptive Server Enterprise 7066 Net 30 USA 6380 Net 60 USA 5023 Net 60 USA (7 rows affected) You can use the position number of a column in a select list instead of the column name. Column names and select list numbers can be mixed. Both of the following statements produce the same results as the preceding one. select pub_id, type, title_id from titles order by 1 desc, 2, 3 select pub_id, type, title_id from titles order by 1 desc, type, 3 Most versions of SQL require that order by items appear in the select list, but Transact-SQL has no such restriction. You could order the results of the preceding query by title, although that column does not appear in the select list. Note You cannot use order by on text or image columns. Adaptive Server does not allow subqueries, aggregates, variables and constant expressions in the order by list. With order by, null values come before all others. The effects of an order by clause on mixed-case data depend on the sort order installed on your Adaptive Server. The basic choices are binary, dictionary order, and case-insensitive. The system procedure sp_helpsort displays the sort order for your server. See the Reference Manual for more information on sort orders. order by and group by You can use an order by clause to order the results of a group by in a particular way. Put the order by clause after the group by clause. For example, to find the average price of each type of book and order the results by average price, the statement is: select type, avg(price) from titles CHAPTER 3 Using Aggregates, Grouping, and Sorting Transact-SQL User’s Guide 105 group by type order by avg(price) type ---------- ------------ UNDECIDED NULL mod_cook 11.49 psychology 13.50 business 13.73 trad_cook 15.96 popular_comp 21.48 (6 rows affected) order by and group by used with select distinct A select distinct query with order by or group by can return duplicate values if the order by or group by column is not in the select list. For example: select distinct pub_id from titles order by type pub_id ------ 0877 0736 1389 0877 1389 0736 0877 0877 (8 rows affected) If a query has an order by or group by clause that includes columns not in the select list, Adaptive Server adds those columns as hidden columns in the columns being processed. The columns listed in the order by or group by clause are included in the test for distinct rows. To comply with ANSI standards, include the order by or group by column in the select list. For example: select distinct pub_id, type from titles order by type pub_id type ------ ------------Summarizing groups of data: the compute clause 106 Adaptive Server Enterprise 0877 UNDECIDED 0736 business 1389 business 0877 mod_cook 1389 popular_comp 0736 psychology 0877 psychology 0877 trad_cook (8 rows affected) Summarizing groups of data: the compute clause The compute clause is a Transact-SQL extension. Use it with row aggregates to produce reports that show subtotals of grouped summaries. Such reports, usually produced by a report generator, are called control-break reports, since summary values appear in the report under the control of the groupings (“breaks”) you specify in the compute clause. These summary values appear as additional rows in the query results, unlike the aggregate results of a group by clause, which appear as new columns. A compute clause allows you to see detail and summary rows with one select statement. You can calculate summary values for subgroups and you can calculate more than one row aggregate (see “Row aggregates and compute” on page 109) for the same group. The general syntax for compute is: compute row_aggregate(column_name) [, row_aggregate(column_name)]... [by column_name [, column_name]...] The row aggregates you can use with compute are sum, avg, min, max, and count. You can use sum and avg only with numeric columns. Unlike the order by clause, you cannot use the positional number of a column from the select list instead of the column name. Note You cannot use text or image columns in a compute clause. CHAPTER 3 Using Aggregates, Grouping, and Sorting Transact-SQL User’s Guide 107 A system test may fail because there are too many aggregates in the compute clause of a query. The number of aggregates that each compute clause can accommodate is limited to 127, and if a compute clause contains more than 127 aggregates, the system generates an error message when you try to execute the query. Each avg() aggregate counts as two aggregates when you are counting toward the limit of 127, because an avg() aggregate is actually a combination of a sum() aggregate and a count() aggregate. Following are two queries and their results. The first one uses group by and aggregates. The second uses compute and row aggregates. Note the difference in the results. select type, sum(price), sum(advance) from titles group by type type ------------ ------- ---------- UNDECIDED NULL NULL business 54.92 25,125.00 mod_cook 22.98 15,000.00 popular_comp 42.95 15,000.00 psychology 67.52 21,275.00 trad_cook 47.89 19,000.00 (6 rows affected) select type, price, advance from titles order by type compute sum(price), sum(advance) by type type price advance ------------ ------------------------ -------- UNDECIDED NULL NULL Compute Result: ------------------------ ------------------------ NULL NULL type price advance ------------ -------------------- ---------- business 2.99 10,125.00 business 11.95 5,000.00 business 19.99 5,000.00 business 19.99 5,000.00 Compute Result:Summarizing groups of data: the compute clause 108 Adaptive Server Enterprise ------------------------ ------------------------ 54.92 25,125.00 type price advance ------------ ----------------------- --------- mod_cook 2.99 15,000.00 mod_cook 19.99 0.00 Compute Result: ------------------------ ------------------------ 22.98 15,000.00 type price advance ------------- ------------------- ------------ popular_comp NULL NULL popular_comp 20.00 8,000.00 popular_comp 22.95 7,000.00 Compute Result: ------------------------ ------------------------ 42.95 15,000.00 type price advance ------------ ------------------------ -------- psychology 7.00 6,000.00 psychology 7.99 4,000.00 psychology 10.95 2,275.00 psychology 19.99 2,000.00 psychology 21.59 7,000.00 Compute Result: ------------------------ ------------------------ 67.52 21,275.00 type price advance ------------ ----------------------- -------- trad_cook 11.95 4,000.00 trad_cook 14.99 8,000.00 trad_cook 20.95 7,000.00 Compute Result: ------------------------ ------------------------ 47.89 19,000.00 (24 rows affected) Each summary value is treated as a row.CHAPTER 3 Using Aggregates, Grouping, and Sorting Transact-SQL User’s Guide 109 Row aggregates and compute The row aggregates used with compute are listed in Table 3-2: Table 3-2: How aggregates are used with a compute statement These row aggregates are the same aggregates that can be used with group by, except there is no row aggregate function that is the equivalent of count(*). To find the summary information produced by group by and count(*), use a compute clause without the by keyword. Rules for compute clauses • Adaptive Server does not allow the distinct keyword with the row aggregates. • The columns in a compute clause must appear in the select list. • You cannot use select into (see Chapter 8, “Creating Databases and Tables”) in the same statement as a compute clause because statements that include compute do not generate normal rows. • If you use compute with the by keyword, you must also use an order by clause. The columns listed after by must be identical to, or a subset of, those listed after order by, and must be in the same left-to-right order, start with the same expression, and not skip any expressions. For example, suppose the order by clause is: order by a, b, c The compute clause can be any or all of these: compute row_aggregate (column_name) by a, b, c compute row_aggregate (column_name) by a, b compute row_aggregate (column_name) by a The compute clause cannot be any of these: compute row_aggregate (column_name) by b, c Row aggregates Result sum Total of the values in the expression avg Average of the values in the expression max Highest value in the expression min Lowest value in the expression count Number of selected rowsSummarizing groups of data: the compute clause 110 Adaptive Server Enterprise compute row_aggregate (column_name) by a, c compute row_aggregate (column_name) by c You must use a column name or an expression in the order by clause; you cannot sort by a column heading. • The compute keyword can be used without by to generate grand totals, grand counts, and so on. order by is optional if you use the compute keyword without by. The compute keyword without by is discussed under “Grand values: compute without by” on page 113. Specifying more than one column after compute Listing more than one column after the by keyword affects the query by breaking a group into subgroups and applying the specified row aggregate to each level of grouping. For example, this query finds the sum of the prices of psychology books from each publisher: select type, pub_id, price from titles where type = "psychology" order by type, pub_id, price compute sum(price) by type, pub_id type pub_id price ----------- ------- ------------- psychology 0736 7.00 psychology 0736 7.99 psychology 0736 10.95 psychology 0736 19.99 Compute Result: --------------- 45.93 type pub_id price ----------- ------- ------------- psychology 0877 21.59 Compute Result: --------------- 21.59 (7 rows affected) CHAPTER 3 Using Aggregates, Grouping, and Sorting Transact-SQL User’s Guide 111 Using more than one compute clause You can use different aggregates in the same statement by including more than one compute clause. The following query is similar to the preceding one but adds the sum of the prices of psychology books by publisher: select type, pub_id, price from titles where type = "psychology" order by type, pub_id, price compute sum(price) by type, pub_id compute sum(price) by type type pub_id price ----------- ------- -------------- psychology 0736 7.00 psychology 0736 7.99 psychology 0736 10.95 psychology 0736 19.99 Compute Result: --------------- 45.93 type pub_id price ---------- ------- -------------- psychology 0877 21.59 Compute Result: --------------- 21.59 Compute Result: --------------- 67.52 (8 rows affected) Applying an aggregate to more than one column One compute clause can apply the same aggregate to several columns. This query finds the sum of the prices and advances for each type of cookbook: select type, price, advance from titles where type like "%cook" Summarizing groups of data: the compute clause 112 Adaptive Server Enterprise order by type compute sum(price), sum(advance) by type type price advance --------- ---------------- --------------- mod_cook 2.99 15,000.00 mod_cook 19.99 0.00 Compute Result: --------------- --------------- 22.98 15,000.00 type price advance --------- ---------------- --------------- trad_cook 11.95 4,000.00 trad_cook 14.99 8,000.00 trad_cook 20.95 7,000.00 Compute Result: --------------- --------------- 47.89 19,000.00 (7 rows affected) Remember, the columns to which the aggregates apply must also be in the select list. Using different aggregates in the same compute clause You can use different aggregates in the same compute clause: select type, pub_id, price from titles where type like "%cook" order by type, pub_id compute sum(price), max(pub_id) by type type pub_id price ----------- ------- -------------- mod_cook 0877 2.99 mod_cook 0877 19.99 Compute Result: --------------- ---- 22.98 0877 type pub_id price CHAPTER 3 Using Aggregates, Grouping, and Sorting Transact-SQL User’s Guide 113 ----------- ------- -------------- trad_cook 0877 11.95 trad_cook 0877 14.99 trad_cook 0877 20.95 Compute Result: --------------- ---- 47.89 0877 (7 rows affected) Grand values: compute without by You can use the compute keyword without by to generate grand totals, grand counts, and so on. This statement finds the grand total of the prices and advances of all types of books that cost more than $20: select type, price, advance from titles where price > $20 compute sum(price), sum(advance) type price advance ------------ ---------------- ------------- popular_comp 22.95 7,000.00 psychology 21.59 7,000.00 trad_cook 20.95 7,000.00 Compute Result: --------------- --------- 65.49 21,000.00 (4 rows affected) You can use a compute with by and a compute without by in the same query. The following query finds the sum of prices and advances by type and then computes the grand total of prices and advances for all types of books. select type, price, advance from titles where type like "%cook" order by type compute sum(price), sum(advance) by type compute sum(price), sum(advance) type price advanceCombining queries: the union operator 114 Adaptive Server Enterprise ----------- ----------------- ------------ mod_ cook 2.99 15,000.00 mod_cook 19.99 0.00 Compute Result: --------------- --------- 22.98 15,000.00 type price advance ----------- ----------------- ------------ trad_cook 11.95 4,000.00 trad_cook 14.99 8,000.00 trad_cook 20.95 7,000.00 Compute Result: --------------- --------- 47.89 19,000.00 Compute Result: --------------- --------- 70.87 34,000.00 (8 rows affected) Combining queries: the union operator The union operator combines the results of two or more queries into a single result set. The Transact-SQL extension to union allows you to: • Use union in the select clause of an insert statement. • Specify new column headings in the order by clause of a select statement when union is present in the select statement. The syntax of the union operator is as follows: query1 [union [all] queryN ] ... [order by clause] [compute clause] where query1 is: select select_list [into clause]CHAPTER 3 Using Aggregates, Grouping, and Sorting Transact-SQL User’s Guide 115 [from clause] [where clause] [group by clause] [having clause] and queryN is: select select_list [from clause] [where clause] [group by clause] [having clause] Figure 3-1: Union combining queries For example, suppose you have the following two tables containing the data shown: The following query creates a union between the two tables: create table T1 (a char(4), b int) insert T1 values ("abc", 1) insert T1 values ("def", 2) insert T1 values ("ghi", 3) create table T2 (a char(4), b int) insert T2 values ("ghi", 3) insert T2 values ("jkl", 4) insert T2 values ("mno", 5) select * from T1 union select * from T2 a b ---- --------- abc 1 def 2 ghi 3 Combining queries: the union operator 116 Adaptive Server Enterprise jkl 4 mno 5 (5 rows affected) By default, the union operator removes duplicate rows from the result set. Use the all option to include duplicate rows. Notice also that the columns in the result set have the same names as the columns in T1. You can use any number of union operators in a Transact-SQL statement. For example: x union y union z By default, Adaptive Server evaluates a statement containing union operators from left to right. You can use parentheses to specify a different evaluation order. For example, the following two expressions are not equivalent: x union all (y union z) (x union all y) union z In the first expression, duplicates are eliminated in the union between y and z. Then, in the union between that set and x, duplicates are not eliminated. In the second expression, duplicates are included in the union between x and y, but are then eliminated in the subsequent union with z; all does not affect the final result of this statement. Guidelines for union queries When you use union statements: • All select lists in the union statement must have the same number of expressions (such as column names, arithmetic expressions, and aggregate functions). The following statement is invalid because the first select list is longer than the second: create table stores_east (stor_id char(4) not null, stor_name varchar(40) null, stor_address varchar(40) null, city varchar(20) null, state char(2) null, country varchar(12) null, postalcode char(10) null, payterms varchar(12) null)CHAPTER 3 Using Aggregates, Grouping, and Sorting Transact-SQL User’s Guide 117 select stor_id, city, state from stores union select stor_id, city from stores_east drop table stores_east • Corresponding columns in all tables, or any subset of columns used in the individual queries, must be of the same datatype, or an implicit data conversion must be possible between the two datatypes, or an explicit conversion should be supplied. For example, a union is not possible between a column of the char datatype and one of the int datatype, unless an explicit conversion is supplied. However, a union is possible between a column of the money datatype and one of the int datatype. See union and “Datatype Conversion Functions” in the Reference Manual for more information about comparing datatypes in a union statement. • You must place corresponding columns in the individual queries of a union statement in the same order, because union compares the columns one to one in the order given in the query. For example, suppose you have the following tables: Figure 3-2: Union comparing columns This query: select a, b from T3 union select b, a from T4 produces: a bCombining queries: the union operator 118 Adaptive Server Enterprise --------- --- 1 abc 2 def 3 ghi (3 rows affected) The following query results in an error message, because the datatypes of corresponding columns are not compatible: select a, b from T3 union select a, b from T4 drop table T3 drop table T4 When you combine different (but compatible) datatypes such as float and int in a union statement, Adaptive Server converts them to the datatype with the most precision. • Adaptive Server takes the column names in the table resulting from a union from the first individual query in the union statement. Therefore, to define a new column heading for the result set, do so in the first query. In addition, to refer to a column in the result set by a new name, for example, in an order by statement, refer to it in that way in the first select statement. The following query is correct: select Cities = city from stores union select city from authors order by Cities Using union with other Transact-SQL commands When you use union statements with other Transact-SQL commands: • The first query in the union statement may contain an into clause that creates a table to hold the final result set. For example, the following statement creates a table called results that contains the union of tables publishers, stores, and salesdetail: use master sp_dboption pubs2, "select into", trueCHAPTER 3 Using Aggregates, Grouping, and Sorting Transact-SQL User’s Guide 119 use pubs2 checkpoint select pub_id, pub_name, city into results from publishers union select stor_id, stor_name, city from stores union select stor_id, title_id, ord_num from salesdetail You can use the into clause only in the first query; if it appears anywhere else, you get an error message. • You can use order by and compute clauses only at the end of the union statement to define the order of the final results or to compute summary values. You cannot use them within the individual queries that make up the union statement. • You can use group by and having clauses within individual queries only; you cannot use them to affect the final result set. • You can also use the union operator within an insert statement. For example: create table tour (city varchar(20), state char(2)) insert into tour select city, state from stores union select city, state from authors drop table tour • Starting with Adaptive Server version 12.5, you can use the union operator within a create view statement. If you are using an earlier version of Adaptive Server, however, you cannot use the union operator within a create view statement. • You cannot use the union operator on text and image columns. • You cannot use the for browse clause in statements involving the union operator. Combining queries: the union operator 120 Adaptive Server EnterpriseTransact-SQL User’s Guide 121 C H A P T E R 4 Subqueries: Using Queries Within Other Queries A subquery is a select statement that is nested inside another select, insert, update, or delete statement, inside a conditional statement, or inside another subquery. This chapter discusses: You can also express subqueries as join operations. See Chapter 6, “Joins: Retrieving Data from Several Tables.” How subqueries work Subqueries, also called inner queries, appear within a where or having clause of another SQL statement or in the select list of a statement. You can use subqueries to handle query requests that are expressed as the results of other queries. A statement that includes a subquery operates on rows from one table, based on its evaluation of the subquery’s select list, which can refer either to the same table as the outer query, or to a different table. In Transact-SQL, a subquery can also be used almost anywhere an expression is allowed, if the subquery returns a single value. A case expression can also include a subquery. For example, this subquery lists the names of all authors whose royalty split is more than $75: select au_fname, au_lname from authors where au_id in (select au_id Topic Page How subqueries work 121 Types of subqueries 130 Using correlated subqueries 148How subqueries work 122 Adaptive Server Enterprise from titleauthor where royaltyper > 75) select statements that contain one or more subqueries are sometimes called nested queries or nested select statements. You can formulate as joins many SQL statements that include a subquery. Other questions can be posed only with subqueries. Some people find subqueries easier to understand. Other SQL users avoid subqueries whenever possible. You can choose whichever formulation you prefer. The result of a subquery that returns no values is NULL. If a subquery returns NULL, the query failed. Subquery syntax Always enclose the select statement of a subquery in parentheses. The select syntax for a subquery is somewhat restricted: (select [all | distinct] subquery_select_list [from_clause] [where search_conditions] [group by aggregate_free_expression [, aggregate_free_expression]...] [having search_conditions]) from_clause ::= from table_reference [,table_reference]... table_reference ::= table_view_name | ANSI_join table_view_name ::= {table_view_reference | derived_table_reference} [holdlock | noholdlock] [shared] table_view_reference ::= [[database.]owner.]{table_name | view_name} [[as] correlation_name ] [index {index_name | table_name }] [prefetch size ] [lru | mru]}} derived_table_reference ::= derived_table [as] correlation_name [‘(‘ derived_column_list’)’] derived_column_list ::= column_name [’,’ column_name] derived_table ::= ’(’ select ’)’CHAPTER 4 Subqueries: Using Queries Within Other Queries Transact-SQL User’s Guide 123 Subquery restrictions A subquery is subject to the following restrictions: • The subquery_select_list can consist of only one column name, except in the exists subquery, where an (*) is usually used in place of the single column name. Do not specify more than one column name. Qualify column names with table or view names if there is ambiguity about the table or view to which they belong. • Subqueries can be nested inside the where or having clause of an outer select, insert, update, or delete statement, inside another subquery, or in a select list. Alternatively, you can write many statements that contain subqueries as joins; Adaptive Server processes such statements as joins. • In Transact-SQL, a subquery can appear almost anywhere an expression can be used, if it returns a single value. • A subquery can appear almost anywhere an expression can be used. SQL derived tables can therefore be used in the from clause of a subquery wherever the subquery is used. • You cannot use subqueries in an order by, group by, or compute by list. • You cannot include a for browse clause in a subquery. • You cannot include a union clause in a subquery unless it is part of a derived table expression within the subquery. For more information on using SQL derived tables, see Chapter 5, “SQL Derived Tables.”. • The select list of an inner subquery introduced with a comparison operator can include only one expression or column name, and the subquery must return a single value. The column you name in the where clause of the outer statement must be join-compatible with the column you name in the subquery select list. • text and image datatypes are not allowed in subqueries. • Subqueries cannot manipulate their results internally, that is, a subquery cannot include the order by clause, the compute clause, or the into keyword. • Correlated (repeating) subqueries are not allowed in the select clause of an updatable cursor defined by declare cursor. • There is a limit of 16 nesting levels. • The maximum number of subqueries on each side of a union is 16.How subqueries work 124 Adaptive Server Enterprise • The where clause of a subquery can contain an aggregate function only if the subquery is in a having clause of an outer query and the aggregate value is a column from a table in the from clause of the outer query. • The result expression from a subquery is subject to the same limits as for any expression. The maximum length of an expression is 16K. For more information, see Chapter 4, “Expressions, Identifiers, and Wildcard “Characters” in the Adaptive Server Reference Manual. Example of using a subquery Suppose you want to find the books that have the same price as Straight Talk About Computers. First, you find the price of Straight Talk: select price from titles where title = "Straight Talk About Computers" price ------------- $19.99 (1 row affected) You use the results of the first query in a second query to find all the books that cost the same as Straight Talk: select title, price from titles where price = $19.99 title price ------------------------------------------ ----- The Busy Executive’s Database Guide 19.99 Straight Talk About Computers 19.99 Silicon Valley Gastronomic Treats 19.99 Prolonged Data Deprivation: Four Case Studies 19.99 (4 rows affected) You can use a subquery to receive the same results in only one step: select title, price from titles where price = (select price from titles where title = "Straight Talk About Computers") CHAPTER 4 Subqueries: Using Queries Within Other Queries Transact-SQL User’s Guide 125 title price --------------------------------------- ----- The Busy Executive’s Database Guide 19.99 Straight Talk About Computers 19.99 Silicon Valley Gastronomic Treats 19.99 Prolonged Data Deprivation: Four Case Studies 19.99 (4 rows affected) Qualifying column names Column names in a statement are implicitly qualified by the table referenced in the from clause at the same level. In the following example, the table name publishers implicitly qualifies the pub_id column in the where clause of the outer query. The reference to pub_id in the select list of the subquery is qualified by the subquery’s from clause—that is, by the titles table: select pub_name from publishers where pub_id in (select pub_id from titles where type = "business") This is what the query looks like with the implicit assumptions spelled out: select pub_name from publishers where publishers.pub_id in (select titles.pub_id from titles where type = "business") It is never wrong to state the table name explicitly, and you can override implicit assumptions about table names by using explicit qualifications. Subqueries with correlation names As discussed in Chapter 6, “Joins: Retrieving Data from Several Tables,” table correlation names are required in self-joins because the table being joined to itself appears in two different roles. You can also use correlation names in nested queries that refer to the same table in both an inner query and an outer query.How subqueries work 126 Adaptive Server Enterprise For example, you can find authors who live in the same city as Livia Karsen by using this subquery: select au1.au_lname, au1.au_fname, au1.city from authors au1 where au1.city in (select au2.city from authors au2 where au2.au_fname = "Livia" and au2.au_lname = "Karsen") au_lname au_fname city ----------- --------- ------- Green Marjorie Oakland Straight Dick Oakland Stringer Dirk Oakland MacFeather Stearns Oakland Karsen Livia Oakland (5 rows affected) Explicit correlation names make it clear that the reference to authors in the subquery is not the same as the reference to authors in the outer query. Without explicit correlation, the subquery is: select au_lname, au_fname, city from authors where city in (select city from authors where au_fname = "Livia" and au_lname = "Karsen") Alternatively, you can state the above query, as well as other statements in which the subquery and the outer query refer to the same table, as self-joins: select au1.au_lname, au1.au_fname, au1.city from authors au1, authors au2 where au1.city = au2.city and au2.au_lname = "Karsen" and au2.au_fname = "Livia" A subquery restated as a join may not return the results in the same order; additionally, the join may require the distinct keyword to eliminate duplicates. CHAPTER 4 Subqueries: Using Queries Within Other Queries Transact-SQL User’s Guide 127 Multiple levels of nesting A subquery can include one or more subqueries. You can nest up to 16 subqueries in a statement. For example: “Find the names of authors who have participated in writing at least one popular computing book:” select au_lname, au_fname from authors where au_id in (select au_id from titleauthor where title_id in (select title_id from titles where type = "popular_comp") ) au_lname au_fname ---------------------- ------------ Carson Cheryl Dull Ann Locksley Chastity Hunter Sheryl (4 rows affected) The outermost query selects all author names. The next query finds the authors’ IDs, and the innermost query returns the title ID numbers PC1035, PC8888, and PC9999. You can also express this query as a join: select au_lname, au_fname from authors, titles, titleauthor where authors.au_id = titleauthor.au_id and titles.title_id = titleauthor.title_id and type = "popular_comp"How subqueries work 128 Adaptive Server Enterprise Subqueries in update, delete, and insert statements You can nest subqueries in update, delete, and insert statements as well as in select statements. Note Running the sample queries in this section changes the pubs2 database. Ask a System Administrator to help you get a clean copy of the sample database. The following query doubles the price of all books published by New Age Books. The statement updates the titles table; its subquery references the publishers table. update titles set price = price * 2 where pub_id in (select pub_id from publishers where pub_name = "New Age Books") An equivalent update statement using a join is: update titles set price = price * 2 from titles, publishers where titles.pub_id = publishers.pub_id and pub_name = "New Age Books" You can remove all records of sales of business books with this nested select statement: delete salesdetail where title_id in (select title_id from titles where type = "business") An equivalent delete statement using a join is: delete salesdetail from salesdetail, titles where salesdetail.title_id = titles.title_id and type = "business" CHAPTER 4 Subqueries: Using Queries Within Other Queries Transact-SQL User’s Guide 129 Subqueries in conditional statements You can use subqueries in conditional statements. The preceding subquery that removed all records of sales of business books can be rewritten, as shown in the next example, to check for the records before deleting them: if exists (select title_id from titles where type = "business") begin delete salesdetail where title_id in (select title_id from titles where type = "business") end Using subqueries instead of expressions In Transact-SQL, you can substitute a subquery almost anywhere you can use an expression in a select, update, insert, or delete statement. For example, a subquery can compare with a column from the inner table of an outer join. You cannot use a subquery in an order by list or as an expression in the values list in an insert statement. The following statement shows how to find the titles and types of books that have been written by authors living in California and that are also published there: select title, type from titles where title in (select title from titles, titleauthor, authors where titles.title_id = titleauthor.title_id and titleauthor.au_id = authors.au_id and authors.state = "CA") and title in (select title from titles, publishers where titles.pub_id = publishers.pub_id and publishers.state = "CA") title type ----------------------------------- ---------- The Busy Executive’s Database Guide businessTypes of subqueries 130 Adaptive Server Enterprise Cooking with Computers: Surreptitious Balance Sheets business Straight Talk About Computers business But Is It User Friendly? popular_comp Secrets of Silicon Valley popular_comp Net Etiquette popular_comp (6 rows affected) The following statement selects the book titles that have had more than 5000 copies sold, lists their prices, and the price of the most expensive book: select title, price, (select max(price) from titles) from titles where total_sales > 5000 title price ----------------------------------- ----- ------ You Can Combat Computer Stress! 2.99 22.95 The Gourmet Microwave 2.99 22.95 But Is It User Friendly? 22.95 22.95 Fifty Years in Buckingham Palace Kitchens 11.95 22.95 (4 rows affected) Types of subqueries There are two basic types of subqueries: • Expression subqueries are introduced with an unmodified comparison operator, must return a single value, and can be used almost anywhere an expression is allowed in SQL. • Quantified predicate subqueries operate on lists introduced with in or with a comparison operator modified by any or all. Quantified predicate subqueries return 0 or more values. This type is also used as an existence test, introduced with exists. Subqueries of either type are either noncorrelated or correlated (repeating). CHAPTER 4 Subqueries: Using Queries Within Other Queries Transact-SQL User’s Guide 131 • A noncorrelated subquery can be evaluated as if it were an independent query. Conceptually, the results of the subquery are substituted in the main statement, or outer query. This is not how Adaptive Server actually processes statements with subqueries. Noncorrelated subqueries can alternatively be stated as joins and are processed as joins by Adaptive Server. • A correlated subquery cannot be evaluated as an independent query, but can reference columns in a table listed in the from list of the outer query. Correlated subqueries are discussed in detail at the end of this chapter. Expression subqueries Expression subqueries include: • Subqueries in a select list (introduced with in) • Subqueries in a where or having clause connected by a comparison operator (=, !=, >, >=, <, <=) Expression subqueries take the general form: [Start of select, insert, update, delete statement or subquery] where expression comparison_operator (subquery) [End of select, insert, update, delete statement or subquery] An expression consists of a subquery or any combination of column names, constants, and functions connected by arithmetic or bitwise operators. The comparison_operator is one of: Operator Meaning = Equal to > Greater than < Less than >= Greater than or equal to <= Less than or equal to != Not equal to <> Not equal to !> Not greater than !< Not less thanTypes of subqueries 132 Adaptive Server Enterprise If you use a column name in the where or having clause of the outer statement, make sure a column name in the subquery_select_list is join compatible with it. A subquery that is introduced with an unmodified comparison operator (that is, a comparison operator that is not followed by any or all) must resolve to a single value. If such a subquery returns more than one value, Adaptive Server returns an error message. For example, suppose that each publisher is located in only one city. To find the names of authors who live in the city where Algodata Infosystems is located, write a statement with a subquery that is introduced with the comparison operator =: select au_lname, au_fname from authors where city = (select city from publishers where pub_name = "Algodata Infosystems") au_lname au_fname -------------- -------------- Carson Cheryl Bennet Abraham (2 rows affected) Using scalar aggregate functions to guarantee a single value Subqueries that are introduced with unmodified comparison operators often include scalar aggregate functions, because these return a single value. For example, to find the names of books that are priced higher than the current minimum price: select title from titles where price > (select min(price) from titles) title --------------------------------------------------- The Busy Executive’s Database Guide Cooking with Computers: Surreptitious Balance Sheets Straight Talk About Computers Silicon Valley Gastronomic Treats CHAPTER 4 Subqueries: Using Queries Within Other Queries Transact-SQL User’s Guide 133 But Is It User Friendly? Secrets of Silicon Valley Computer Phobic and Non-Phobic Individuals: Behavior Variations Is Anger the Enemy? Life Without Fear Prolonged Data Deprivation: Four Case Studies Emotional Security: A New Algorithm Onions, Leeks, and Garlic: Cooking Secrets of the Mediterranean Fifty Years in Buckingham Palace Kitchens Sushi, Anyone? (14 rows affected) group by and having in expression subqueries Because subqueries that are introduced by unmodified comparison operators must return a single value, they cannot include group by and having clauses unless you know that the group by and having clauses will return a single value. For example, this query finds the books that are priced higher than the lowest priced book in the trad_cook category: select title from titles where price > (select min(price) from titles group by type having type = "trad_cook") Using distinct with expression subqueries Subqueries that are introduced with unmodified comparison operators often include the distinct keyword to ensure the return of a single value. For example, without distinct, this subquery would fail because it would return more than one value: select pub_name from publishers where pub_id = (select distinct pub_id from titles where pub_id = publishers.pub_id)Types of subqueries 134 Adaptive Server Enterprise Quantified predicate subqueries Quantified predicate subqueries, which return a list of 0 and higher values, are subqueries in a where or having clause that are connected by any, all, in, or exists. The any or all subquery operators modify comparison operators. There are three types of quantified predicate subqueries: • any/all subqueries. Subqueries introduced with a modified comparison operator, which may include a group by or having clause, take the general form: [Start of select, insert, update, delete statement; or subquery] where expression comparison_operator [any | all] (subquery) [End of select, insert, update, delete statement; or subquery] • in/not in subqueries. Subqueries introduced with in or not in take the general form: [Start of select, insert, update, delete statement; or subquery] where expression [not] in (subquery) [End of select, insert, update, delete statement; or subquery] • exists/not exists subqueries. Subqueries introduced by exists or not exists are existence tests which take the general form: [Start of select, insert, update, delete statement; or subquery] where [not] exists (subquery) [End of select, insert, update, delete statement; or subquery] Though Adaptive Server allows the keyword distinct in quantified predicate subqueries, it always processes the subquery as if distinct were not included. Subqueries with any and all The keywords all and any modify a comparison operator that introduces a subquery. When any is used with <, >, or = with a subquery, it returns results when any value retrieved in the subquery matches the value in the where or having clause of the outer statement.CHAPTER 4 Subqueries: Using Queries Within Other Queries Transact-SQL User’s Guide 135 When all is used with < or > in a subquery, it returns results when all values retrieved in the subquery match the value in the where or having clause of the outer statement. The syntax for any and all is: {where | having} [not] expression comparison_operator {any | all} (subquery) Using the > comparison operator as an example: • > all means greater than every value, or greater than the maximum value. For example, > all (1, 2, 3) means greater than 3. • > any means greater than at least one value, or greater than the minimum value. Therefore, > any (1, 2, 3) means greater than 1. If you introduce a subquery with all and a comparison operator does not return any values, the entire query fails. all and any can be tricky. For example, you might ask “Which books commanded an advance greater than any book published by New Age Books?” You can paraphrase this question to make its SQL “translation” more clear: “Which books commanded an advance greater than the largest advance paid by New Age Books?” The all keyword, not the any keyword, is required here: select title from titles where advance > all (select advance from publishers, titles where titles.pub_id = publishers.pub_id and pub_name = "New Age Books") title ---------------------------------------- The Gourmet Microwave (1 row affected) For each title, the outer query gets the titles and advances from the titles table, and it compares these to the advance amounts paid by New Age Books returned from the subquery. The outer query looks at the largest value in the list and determines whether the title being considered has commanded an even greater advance. Types of subqueries 136 Adaptive Server Enterprise > all means greater than all values The > all operator means that the value in the column that introduces the subquery must be greater than each of the values returned by the subquery, for a row to satisfy the condition in the outer query. For example, to find the books that are priced higher than the highest-priced book in the mod_cook category: select title from titles where price > all (select price from titles where type = "mod_cook") title --------------------------------------------------- But Is It User Friendly? Secrets of Silicon Valley Computer Phobic and Non-Phobic Individuals: Behavior Variations Onions, Leeks, and Garlic: Cooking Secrets of the Mediterranean (4 rows affected) However, if the set returned by the inner query contains a NULL, the query returns 0 rows. This is because NULL stands for “value unknown,” and it is impossible to tell whether the value you are comparing is greater than an unknown value. For example, try to find the books that are priced higher than the highest-priced book in the popular_comp category: select title from titles where price > all (select price from titles where type = "popular_comp") title --------------------------------------------------- (0 rows affected) No rows were returned because the subquery found that one of the books, Net Etiquette, has a null price. = all means equal to every value The = all operator means that the value in the column that introduces the subquery must be the same as each value in the list of values returned by the subquery, for a row to satisfy the outer query. CHAPTER 4 Subqueries: Using Queries Within Other Queries Transact-SQL User’s Guide 137 For example, the following query finds out which authors live in the same city by looking at the postal code: select au_fname, au_lname, city from authors where city = all (select city from authors where postalcode like "946%") > any means greater than at least one value > any means that the value in the column that introduces the subquery must be greater than at least one of the values in the list returned by the subquery, for a row to satisfy the outer query. The following example is introduced with a comparison operator modified by any. It finds each title that has an advance larger than any advance amount paid by New Age Books. select title from titles where advance > any (select advance from titles, publishers where titles.pub_id = publishers.pub_id and pub_name = "New Age Books") title --------------------------------------------------- The Busy Executive’s Database Guide Cooking with Computers: Surreptitious Balance Sheets You Can Combat Computer Stress! Straight Talk About Computers The Gourmet Microwave But Is It User Friendly? Secrets of Silicon Valley Computer Phobic and Non-Phobic Individuals: Behavior Variations Is Anger the Enemy? Life Without Fear Emotional Security: A New Algorithm Onions, Leeks, and Garlic: Cooking Secrets of the Mediterranean Fifty Years in Buckingham Palace Kitchens Sushi, Anyone? Types of subqueries 138 Adaptive Server Enterprise (14 rows affected) For each title selected by the outer query, the inner query finds a list of advance amounts paid by New Age Books. The outer query looks at all the values in the list and determines whether the title being considered has commanded an advance that is larger than any of those values. In other words, this example finds titles with advances as large as or larger than the lowest value paid by New Age Books. If the subquery does not return any values, the entire query fails. = any means equal to some value The = any operator is an existence check; it is equivalent to in. For example, to find authors that live in the same city as any publisher, you can use either =any or in: select au_lname, au_fname from authors where city = any (select city from publishers) select au_lname, au_fname from authors where city in (select city from publishers) au_lname au_fname -------------- -------------- Carson Cheryl Bennet Abraham (2 rows affected) However, the != any operator is different from not in. The != any operator means “not = a or not = b or not = c”; not in means “not = a and not = b and not = c”. For example, to find the authors who live in a city where no publisher is located: select au_lname, au_fname from authors where city != any (select city from publishers) The results include all 23 authors. This is because every author lives in some city where no publisher is located, and each author lives in only one city. CHAPTER 4 Subqueries: Using Queries Within Other Queries Transact-SQL User’s Guide 139 The inner query finds all the cities in which publishers are located, and then, for each city, the outer query finds the authors who do not live there. Here is what happens when you substitute not in in the same query: select au_lname, au_fname from authors where city not in (select city from publishers) au_lname au_fname -------------- ------------ White Johnson Green Marjorie O’Leary Michael Straight Dick Smith Meander Dull Ann Gringlesby Burt Locksley Chastity Greene Morningstar Blotchet-Halls Reginald Yokomoto Akiko del Castillo Innes DeFrance Michel Stringer Dirk MacFeather Stearns Karsen Livia Panteley Sylvia Hunter Sheryl McBadden Heather Ringer Anne Ringer Albert (21 rows affected) These are the results you want. They include all the authors except Cheryl Carson and Abraham Bennet, who live in Berkeley, where Algodata Infosystems is located. You get the same results if you use !=all, which is equivalent to not in: select au_lname, au_fname from authors where city != all (select city from publishers) Types of subqueries 140 Adaptive Server Enterprise Subqueries used with in Subqueries that are introduced with the keyword in return a list of 0 and higher values. For example, this query finds the names of the publishers who have published business books: select pub_name from publishers where pub_id in (select pub_id from titles where type = "business") pub_name ---------------------------------------- New Age Books Algodata Infosystems (2 rows affected) This statement is evaluated in two steps. The inner query returns the identification numbers of the publishers who have published business books, 1389 and 0736. These values are then substituted in the outer query, which finds the names that go with the identification numbers in the publishers table. The query looks like this: select pub_name from publishers where pub_id in ("1389", "0736") Another way to formulate this query using a subquery is: select pub_name from publishers where "business" in (select type from titles where pub_id = publishers.pub_id) Note that the expression following the where keyword in the outer query can be a constant as well as a column name. You can use other types of expressions, such as combinations of constants and column names. The preceding queries, like many other subqueries, can be alternatively formulated as a join query: select distinct pub_name from publishers, titles where publishers.pub_id = titles.pub_id and type = "business" CHAPTER 4 Subqueries: Using Queries Within Other Queries Transact-SQL User’s Guide 141 Both this query and the subquery versions find publishers who have published business books. All are equally correct and produce the same results, though you may need to use the distinct keyword to eliminate duplicates. However, one advantage of using a join query rather than a subquery for this and similar problems is that a join query shows columns from more than one table in the result. For example, to include the titles of the business books in the result, you would need to use the join version: select pub_name, title from publishers, titles where publishers.pub_id = titles.pub_id and type = "business" pub_name title -------------------- ---------------------------------------- Algodata Infosystems The Busy Executive’s Database Guide Algodata Infosystems Cooking with Computers: Surreptitious Balance Sheets New Age Books You Can Combat Computer Stress! Algodata Infosystems Straight Talk About Computers (4 rows affected) Here is another example of a statement that can be formulated either with a subquery or a join query: “Find the names of all second authors who live in California and receive less than 30 percent of the royalties on a book.” Using a subquery, the statement is: select au_lname, au_fname from authors where state = "CA" and au_id in (select au_id from titleauthor where royaltyper < 30 and au_ord = 2) au_lname au_fname ------------------------ ------------ MacFeather Stearns (1 row affected) The outer query produces a list of the 15 authors who live in California. The inner query is then evaluated, producing a list of the IDs of the authors who meet the qualifications. More than one condition can be included in the where clause of both the inner and the outer query. Types of subqueries 142 Adaptive Server Enterprise Using a join, the query is expressed like this: select au_lname, au_fname from authors, titleauthor where state = "CA" and authors.au_id = titleauthor.au_id and royaltyper < 30 and au_ord = 2 A join can always be expressed as a subquery. A subquery can often be expressed as a join. Subqueries used with not in Subqueries that are introduced with the keyword phrase not in also return a list of 0 and higher values. not in means “not = a and not = b and not = c”. This query finds the names of the publishers who have not published business books, the inverse of the example in “Subqueries used with in” on page 140: select pub_name from publishers where pub_id not in (select pub_id from titles where type = "business") pub_name ---------------------------------------- Binnet & Hardley (1 row affected) The query is the same as the previous one except that not in is substituted for in. However, you cannot convert this statement to a join; the “not equal” join finds the names of publishers who have published some book that is not a business book. The difficulties interpreting the meaning of joins that are not based on equality are discussed in detail in Chapter 6, “Joins: Retrieving Data from Several Tables.” Subqueries using not in with NULL A subquery using not in returns a set of values for each row in the outer query. If the value in the outer query is not in the set returned by the inner query, the not in evaluates to TRUE, and the outer query puts the record being considered in the results.CHAPTER 4 Subqueries: Using Queries Within Other Queries Transact-SQL User’s Guide 143 However, if the set returned by the inner query contains no matching value, but it does contain a NULL, the not in returns UNKNOWN. This is because NULL stands for “value unknown,” and it is impossible to tell whether the value you are looking for is in a set containing an unknown value. The outer query discards the row. For example: select pub_name from publishers where $100.00 not in (select price from titles where titles.pub_id = publishers.pub_id) pub_name ------ New Age Books (1 row affected) New Age Books is the only publisher that does not publish any books that cost $100. Binnet & Handley and Algodata Infosystems were not included in the query results because each publishes a book for which the price is undecided. Subqueries used with exists Use the exists keyword with a subquery to test for the existence of some result from the subquery: {where | having} [not] exists (subquery) That is, the where clause of the outer query tests for the existence of the rows returned by the subquery. The subquery does not actually produce any data, but returns a value of TRUE or FALSE. For example, this query finds the names of all the publishers who publish business books: select pub_name from publishers where exists (select * from titles where pub_id = publishers.pub_id and type = "business") pub_name ---------------------------------------- New Age Books Types of subqueries 144 Adaptive Server Enterprise Algodata Infosystems (2 rows affected) To conceptualize the resolution of this query, consider each publisher’s name in turn. Does this value cause the subquery to return at least one row? In other words, does it cause the existence test to evaluate to TRUE? In the results of the preceding query, the second publisher’s name is Algodata Infosystems, which has an identification number of 1389. Are there any rows in the titles table in which pub_id is 1389 and type is business? If so, “Algodata Infosystems” should be one of the values selected. The same process is repeated for each of the other publisher’s names. A subquery that is introduced with exists is different from other subqueries, in these ways: • The keyword exists is not preceded by a column name, constant, or other expression. • The subquery exists evaluates to TRUE or FALSE rather than returning any data. • The select list of the subquery usually consists of the asterisk (*). There is no need to specify column names, since you are simply testing for the existence or nonexistence of rows that meet the conditions specified in the subquery. Otherwise, the select list rules for a subquery introduced with exists are identical to those for a standard select list. The exists keyword is very important, because there is often no alternative nonsubquery formulation. In practice, a subquery introduced by exists is always a correlated subquery (see “Using correlated subqueries” on page 148). Although you cannot express some queries formulated with exists in any other way, you can express all queries that use in or a comparison operator modified by any or all with exists. Some examples of statements using exists and their equivalent alternatives follow. Here are two ways to find authors that live in the same city as a publisher: select au_lname, au_fname from authors where city = any (select city from publishers) select au_lname, au_fname from authors where exists CHAPTER 4 Subqueries: Using Queries Within Other Queries Transact-SQL User’s Guide 145 (select * from publishers where authors.city = publishers.city) au_lname au_fname -------------- -------------- Carson Cheryl Bennet Abraham (2 rows affected) Here are two queries that find titles of books published by any publisher located in a city that begins with the letter “B”: select title from titles where exists (select * from publishers where pub_id = titles.pub_id and city like "B%") select title from titles where pub_id in (select pub_id from publishers where city like "B%") title --------------------------------------------------- You Can Combat Computer Stress! Is Anger the Enemy? Life Without Fear Prolonged Data Deprivation: Four Case Studies Emotional Security: A New Algorithm The Busy Executive’s Database Guide Cooking with Computers: Surreptitious Balance Sheets Straight Talk About Computers But Is It User Friendly? Secrets of Silicon Valley Net Etiquette (11 rows affected) Types of subqueries 146 Adaptive Server Enterprise Subqueries used with not exists not exists is just like exists except that the where clause in which it is used is satisfied when no rows are returned by the subquery. For example, to find the names of publishers who do not publish business books, the query is: select pub_name from publishers where not exists (select * from titles where pub_id = publishers.pub_id and type = "business") pub_name ---------------------------------------- Binnet & Hardley (1 row affected) This query finds the titles for which there have been no sales: select title from titles where not exists (select title_id from salesdetail where title_id = titles.title_id) title ----------------------------------------- The Psychology of Computer Cooking Net Etiquette (2 rows affected) Finding intersection and difference with exists You can use subqueries that are introduced with exists and not exists for two set theory operations: intersection and difference. The intersection of two sets contains all elements that belong to both of the original sets. The difference contains the elements that belong only to the first set. The intersection of authors and publishers over the city column is the set of cities in which both an author and a publisher are located: select distinct city CHAPTER 4 Subqueries: Using Queries Within Other Queries Transact-SQL User’s Guide 147 from authors where exists (select * from publishers where authors.city = publishers.city) city -------------------- Berkeley (1 row affected) The difference between authors and publishers over the city column is the set of cities where an author lives but no publisher is located, that is, all the cities except Berkeley: select distinct city from authors where not exists (select * from publishers where authors.city = publishers.city) city -------------------- Gary Covelo Oakland Lawrence San Jose Ann Arbor Corvallis Nashville Palo Alto Rockville Vacaville Menlo Park Walnut Creek San Francisco Salt Lake City (15 rows affected) Subqueries using SQL derived tables A SQL derived table can be used in a subquery from clause. For example, this query finds the names of the publishers who have published business books:Using correlated subqueries 148 Adaptive Server Enterprise select pub_name from publishers where "business" in (select type from (select type from titles, publishers where titles.pub_id = publishers.pub_id) dt_titles) Here, dt_titles is the SQL derived table defined by the innermost select statement. SQL derived tables can be used in the from clause of subqueries wherever subqueries are legal. For more information on SQL derived tables, see Chapter 5, “SQL Derived Tables.” Using correlated subqueries You can evaluate many of the previous queries by executing the subquery once and substituting the resulting values into the where clause of the outer query; these are noncorrelated subqueries. In queries that include a repeating subquery, or correlated subquery, the subquery depends on the outer query for its values. The subquery is executed repeatedly, once for each row that is selected by the outer query. This example finds the names of all authors who earn 100 percent royalty on a book: select au_lname, au_fname from authors where 100 in (select royaltyper from titleauthor where au_id = authors.au_id) au_lname au_fname -------------- ---------- White Johnson Green Marjorie Carson Cheryl Straight Dick Locksley Chastity Blotchet-Hall Reginald del Castillo Innes Panteley Sylvia Ringer Albert CHAPTER 4 Subqueries: Using Queries Within Other Queries Transact-SQL User’s Guide 149 (9 rows affected) Unlike most of the previous subqueries, the subquery in this statement cannot be resolved independently of the main query. It needs a value for authors.au_id, but this value is a variable—it changes as Adaptive Server examines different rows of the authors table. This is how the preceding query is evaluated: Transact-SQL considers each row of the authors table for inclusion in the results, by substituting the value in each row in the inner query. For example, suppose Transact-SQL first examines the row for Johnson White. Then, authors.au_id takes the value “172- 32-1176,” which Transact-SQL substitutes for the inner query: select royaltyper from titleauthor where au_id = "172-32-1176" The result is 100, so the outer query evaluates to: select au_lname, au_fname from authors where 100 in (100) Since the where condition is true, the row for Johnson White is included in the results. If you go through the same procedure with the row for Abraham Bennet, you can see how that row is not included in the results. Correlated subqueries containing Transact-SQL outer joins Adaptive Server version 12.5 does not process correlated subqueries containing Transact-SQL outer joins in the same way that earlier versions of Adaptive Server did. The following is an example of a query using a correlated variable as the outer member of a Transact-SQL outer join: select t2.b1, (select t2.b2 from t1 where t2.b1 *= t1.a1) from t2 Earlier versions of Adaptive Server used trace flag 298 to display error messages for these queries. Depending on whether trace flag 298 was turned on or off and whether the query used the correlated variable as an inner or outer member of an outer join, Adaptive Server displayed the behavior described in Table 4-1: Table 4-1: Behavior in earlier versions of Adaptive Server Type of query Trace flag 298 turned off Trace flag 298 turned on Correlated as an inner member of an outer join Disallowed: produces error message 11013 No errorUsing correlated subqueries 150 Adaptive Server Enterprise Adaptive Server reverses the behavior of trace flag 298. Because Adaptive Server version 12.5 translates Transact-SQL outer joins into ANSI outer joins during the preprocessor stage, there is the potential for different results when allowing such queries to run. Allowing correlated subqueries that contain Transact-SQL outer joins to run with the 298 trace flag turned on is consistent with Sybase’s historical trace flag usage. For version 12.5, the behavior of trace flag 298 is: Table 4-2: Behavior in Adaptive Server version 12.5 Adaptive Server has changed error message 301 to error message 11055, although the text of the message remains the same. Correlated subqueries with correlation names You can use a correlated subquery to find the types of books that are published by more than one publisher: select distinct t1.type from titles t1 where t1.type in (select t2.type from titles t2 where t1.pub_id != t2.pub_id) type -------------------- business psychology (2 rows affected) Correlation names are required in the following query to distinguish between the two roles in which the titles table appears. This nested query is equivalent to the self-join query: Correlated as an outer member of an outer join No error Disallowed: produces error message 301 Type of query Trace flag 298 turned off Trace flag 298 turned on Type of query Trace flag 298 turned off Trace flag 298 turned on Correlated as an inner member of an outer join Disallowed: produces error message 11013 Disallowed: produces error message 11013 Correlated as an outer member of an outer join Disallowed: produces error message 11055 No errorCHAPTER 4 Subqueries: Using Queries Within Other Queries Transact-SQL User’s Guide 151 select distinct t1.type from titles t1, titles t2 where t1.type = t2.type and t1.pub_id != t2.pub_id Correlated subqueries with comparison operators Expression subqueries can be correlated subqueries. For example, to find the sales of psychology books where the quantity is less than average for sales of that title: select s1.ord_num, s1.title_id, s1.qty from salesdetail s1 where title_id like "PS%" and s1.qty < (select avg(s2.qty) from salesdetail s2 where s2.title_id = s1.title_id) ord_num title_id qty ------------------ -------- --- 91-A-7 PS3333 90 91-A-7 PS2106 30 55-V-7 PS2106 31 AX-532-FED-452-2Z7 PS7777 125 BA71224 PS7777 200 NB-3.142 PS2091 200 NB-3.142 PS7777 250 NB-3.142 PS3333 345 ZD-123-DFG-752-9G8 PS3333 750 91-A-7 PS7777 180 356921 PS3333 200 (11 rows affected) The outer query selects the rows of the sales table (or “s1”) one by one. The subquery calculates the average quantity for each sale being considered for selection in the outer query. For each possible value of s1, Transact-SQL evaluates the subquery and puts the record being considered in the results, if the quantity is less than the calculated average. Sometimes a correlated subquery mimics a group by statement. To find the titles of books that have prices higher than average for books of the same type, the query is: select t1.type, t1.title Using correlated subqueries 152 Adaptive Server Enterprise from titles t1 where t1.price > (select avg(t2.price) from titles t2 where t1.type = t2.type) type title --------- -------------------------------------- business The Busy Executive’s Database Guide business Straight Talk About Computers mod_cook Silicon Valley Gastronomic Treats popular_comp But Is It User Friendly? psychology Computer Phobic and Non-Phobic Individuals: Behavior Variations psychology Prolonged Data Deprivation: Four Case Studies trad_cook Onions, Leeks, and Garlic: Cooking Secrets of the Mediterranean (7 rows affected) For each possible value of t1, Transact-SQL evaluates the subquery and includes the row in the results if the price value of that row is greater than the calculated average. It is not necessary to group by type explicitly, because the rows for which the average price is calculated are restricted by the where clause in the subquery. Correlated subqueries in a having clause Quantified predicate subqueries can be correlated subqueries. This example of a correlated subquery in the having clause of an outer query finds the types of books in which the maximum advance is more than twice the average within a given group: select t1.type from titles t1 group by t1.type having max(t1.advance) >= any (select 2 * avg(t2.advance) from titles t2 where t1.type = t2.type) type ---------- mod_cook CHAPTER 4 Subqueries: Using Queries Within Other Queries Transact-SQL User’s Guide 153 (1 row affected) The subquery above is evaluated once for each group that is defined in the outer query, that is, once for each type of book.Using correlated subqueries 154 Adaptive Server EnterpriseTransact-SQL User’s Guide 155 C H A P T E R 5 SQL Derived Tables A SQL derived table is defined by one or more tables through the evaluation of a query expression. A SQL derived table is used in the query expression in which it is defined and exists only for the duration of the query. It is not described in system catalogs or stored on disk. This chapter discusses: Differences from abstract plan derived tables SQL derived tables should not be confused with abstract plan derived tables. An abstract plan derived table is a derived table used in query processing, the optimization and execution of queries. An abstract plan derived table differs from a SQL derived table in that it exists as part of an abstract plan and is invisible to the end user. How SQL derived tables work A SQL derived table is created with a derived table expression consisting of a nested select statement, as in the following example, which returns a list of cities in the publishers table of the pubs2 database: select city from (select city from publishers) cities Topic Page Differences from abstract plan derived tables 155 How SQL derived tables work 155 Advantages of SQL derived tables 156 SQL derived table syntax 157 Using SQL derived tables 160Advantages of SQL derived tables 156 Adaptive Server Enterprise The SQL derived table is named cities and has one column titled city. The SQL derived table is defined by the nested select statement and persists only for the duration of the query, which returns the following: city -------------------- Boston Washington Berkeley Advantages of SQL derived tables A user interested in viewing only the titles of books written in Colorado might create a view like the following: create view vw_colorado_titles as select title from titles, titleauthor, authors where titles.title_id = titleauthor.title_id and titleauthor.au_id = authors.au_id and authors.state = “CO” The view vw_colorado_titles, stored in memory, can be used repeatedly to display its results: select * from vw_colorado_titles Once the view is no longer needed, it is dropped: drop view vw_colorado_titles If the query results are only needed once, the user might instead use a SQL derived table: select title from (select title from titles, titleauthor, authors where titles.title_id = titleauthor.title_id and titleauthor.au_id = authors.au_id and authors.state = “CO”) dt_colo_titles The SQL derived table created is named dt_colo_titles. The SQL derived table persists only for the duration of the query, in contrast with a temporary table, which exists for the entire session.CHAPTER 5 SQL Derived Tables Transact-SQL User’s Guide 157 In the previous example for query results that are only needed once, a view is less desirable than a SQL derived table query because the view is more complicated, requiring both create and drop statements in addition to a select statement. The benefits of creating a view for only one query are additionally offset by the overhead of administrative tasks such as dealing with system catalogs. SQL derived tables eliminate this overhead by enabling queries to spontaneously create non-persistent tables without needing to drop the tables or make insertions into the system catalog. Consequently, no administrative tasks are required. A SQL derived table used multiple times performs comparably to a query using a view with a cached definition. SQL derived tables and optimization Queries expressed as a single SQL statement exploit the optimizer better than queries expressed in two or more SQL statements. SQL derived tables enable one to concisely express in a single step what might otherwise require several SQL statements and temporary tables, especially where intermediate aggregate results must be stored. For example, select dt_1.* from (select sum(total_sales) from titles_west group by total_sales) dt_1(sales_sum), (select sum(total_sales) from titles_east group by total_sales) dt_2(sales_sum) where dt_1.sales_sum = dt_2.sales_sum Here aggregate results are obtained from the SQL derived tables dt_1 and dt_2, and a join is computed between the two SQL derived tables. Everything is accomplished in a single SQL statement. SQL derived table syntax The query expression for a SQL derived table is specified in the from clause of the select or select into command in place of a table or view name: from_clause ::= from table_reference [,table_reference]... table_reference ::= table_view_name | ANSI_joinSQL derived table syntax 158 Adaptive Server Enterprise table_view_name ::= {table_view_reference | derived_table_reference} [holdlock | noholdlock] [readpast] [shared] table_view_reference ::= [[database.]owner.] {table_name | view_name} [[as] correlation_name] [index {index_name | table_name }] [parallel [degree_of_parallelism]] [prefetch size ] [lru | mru] derived_table_reference ::= derived_table [as] correlation_name [’(’ derived_column_list’)’] derived_column_list ::= column_name [’,’ column_name] ... derived_table ::= ’(’ select ’)’ A derived table expression is similar to the select in a create view statement and follows the same rules, with the following exceptions: • Temporary tables are permitted in a derived table expression except when it is part of a create view statement. • A local variable is permitted in a derived table expression except when it is part of a create view statement. You cannot assign a value to a variable within a derived table expression. • A correlation_name, which must follow the derived table expression to specify the name of the SQL derived table, may omit a derived column list, whereas a view cannot have unnamed columns: select * from (select sum(advance) from total_sales) dt For information on view restrictions, refer to "Restrictions on views" in the section describing the create view command. CHAPTER 5 SQL Derived Tables Transact-SQL User’s Guide 159 Derived column lists If a derived column list is not included in a SQL derived table, the names of the SQL derived table columns must match the names of the columns specified in the target list of the derived table expression. If a column name is not specified in the target list of the derived table expression, as in the case where a constant expression or an aggregate is present in the target list of the derived table expression, the resulting column in the SQL derived table has no name. If a derived column list is included in a SQL derived table, it must specify names for all columns in the target list of the derived table expression. These column names must be used in the query block in place of the natural column names of the SQL derived table. The columns must be listed in the order in which they occur in the derived table expression, and a column name cannot be specified more than once in the derived column list. Correlated SQL derived tables Correlated SQL derived tables, which are not ANSI standard, are not supported. For example, the following query is not supported because it references the SQL derived table dt_publishers2 inside the derived table expression for dt_publishers1: select * from (select * from titles where titles.pub_id = dt_publishers2.pub_id) dt_publishers1, (select * from publishers where city = "Boston") dt_publishers2 where dt_publishers1.pub_id = dt_publishers2.pub_id Similarly, the following query is not supported because the derived table expression for dt_publishers references the publishers_pub_id column, which is outside the scope of the SQL derived table: select * from publishers where pub_id in (select pub_id from (select pub_id from titles where pub_id = publishers.pub_id) dt_publishers) The following query illustrates proper referencing and is supported: select * from publishers where pub_id in (select pub_id from (select pub_id from titles)Using SQL derived tables 160 Adaptive Server Enterprise dt_publishers where pub_id = publishers.pub_id) Using SQL derived tables SQL derived tables can be used to form part of a larger integrated query using assorted SQL clauses and operators. Nesting A query can use numerous nested derived table expressions, SQL expressions that define a SQL derived table. In the following example, the innermost derived table expression defines SQL derived table dt_1, the select from which forms the derived table expression defining SQL derived table dt_2. select postalcode from (select postalcode from (select postalcode from authors) dt_1) dt_2 The degree of nesting is limited to 25. Subqueries using SQL derived tables A SQL derived table can be used in a subquery from clause. For example, this query finds the names of the publishers who have published business books: select pub_name from publishers where "business" in (select type from (select type from titles, publishers where titles.pub_id = publishers.pub_id) dt_titles) Here, dt_titles is the SQL derived table defined by the innermost select statement. SQL derived tables can be used in the from clause of subqueries wherever subqueries are legal. For more information on subqueries, see Chapter 4, “Subqueries: Using Queries Within Other Queries”.CHAPTER 5 SQL Derived Tables Transact-SQL User’s Guide 161 Unions A union clause is allowed within a derived table expression. For example, the following query yields the contents of the stor_id and ord_num columns of both the sales and sales_east tables: select * from (select stor_id, ord_num from sales union select stor_id, ord_num from sales_east) dt_sales_info Here, the union of two select operations defines the SQL derived table dt_sales_info. Unions in subqueries A union clause is allowed in a subquery inside a derived table expression. The following example uses a union clause in a subquery within a SQL derived table to list the titles of books sold at stores listed in the sales and sales_east tables: select title_id from salesdetail where stor_id in (select stor_id from (select stor_id from sales union select stor_id from sales_east) dt_stores) Renaming columns with SQL derived tables While a view cannot have unnamed columns, column naming is optional for a SQL derived table. If a derived column list is included for a SQL derived table, it follows the name of the SQL derived table and is enclosed in parentheses, as in the following example: select dt_b.book_title, dt_b.tot_sales from (select title, total_sales from titles) dt_b (book_title, tot_sales) where dt_b.book_title like "%Computer%"Using SQL derived tables 162 Adaptive Server Enterprise Here the column names title and total_sales in the derived table expression are respectively renamed to book_title and tot_sales using the derived column list. The book_title and tot_sales column names are used in the rest of the query. Constant expressions If a column name is not specified in the target list of the derived table expression, as in the case where a constant expression is used for the column name, the resulting column in the SQL derived table has no name: 1> select * from 2> (select title_id, (lorange + hirange)/2 3> from roysched) as dt_avg_range 4> go title_id --------- ----------- BU1032 2500 BU1032 27500 PC1035 1000 PC1035 2500 You can specify column names for the target list of a derived table expression using a derived column list: 1> select * from 2> (select title_id, (lorange + hirange)/2 3> from roysched) as dt_avg_range (title, avg_range) 4> go title avg_range --------- ----------- BU1032 2500 BU1032 27500 PC1035 1000 PC1035 2500 Alternately, you can specify column names by renaming the column in the target list of the derived table expression: 1> select * from 2> (select title_id, (lorange + hirange)/2 avg_range 3> from roysched) as dt_avg_range 4> goCHAPTER 5 SQL Derived Tables Transact-SQL User’s Guide 163 title avg_range --------- ----------- BU1032 2500 BU1032 27500 PC1035 1000 PC1035 2500 Note If you specify column names in both a derived column list and in the target list of the derived table expression, the resulting columns are named by the derived column list. The column names in a derived column list take precedence over the names specified in the target list of the derived table expression. If you use a constant expression within a create view statement, you must specify a column name for the constant expression results. Aggregate functions Derived table expressions may use aggregate functions, such as sum, avg, max, min, and count. The following example selects columns pub_id and adv_sum from the SQL derived table dt_a. The second column is created in the derived table expression using the sum function over the advance column of the titles table. select dt_a.pub_id, dt_a.adv_sum from (select pub_id, sum(advance) adv_sum from titles group by pub_id) dt_a If you use an aggregate function within a create view statement, you must specify a column name for the aggregate results. Joins with SQL derived tables The following example illustrates a join between a SQL derived table and an existing table. The join is specified by the where clause. The two tables joined are dt_c, a SQL derived table, and publishers, an existing table in the pubs2 database. select dt_c.title_id, dt_c.pub_id from (select title_id, pub_id from titles) as dt_c,Using SQL derived tables 164 Adaptive Server Enterprise publishers where dt_c.pub_id = publishers.pub_id The following example illustrates a join between two SQL derived tables. The two tables joined are dt_c and dt_d. select dt_c.title_id, dt_c.pub_id from (select title_id, pub_id from titles) as dt_c, (select pub_id from publishers) as dt_d where dt_c.pub_id = dt_d.pub_id Outer joins involving SQL derived tables are also possible. Sybase supports both left and right outer joins. The following example illustrates a left outer join between two SQL derived tables. select dt_c.title_id, dt_c.pub_id from (select title_id, pub_id from titles) as dt_c, (select title_id, pub_id from publishers) as dt_d where dt_c.title_id *= dt_d.title_id The following example illustrates a left outer join within a derived table expression. select dt_titles.title_id from (select * from titles, titleauthor where titles.title_id *= titleauthor.title_id) dt_titles Creating a table from a SQL derived table Data obtained from a SQL derived table can then be inserted into a new table, as in the following example. select pubdate into pub_dates from (select pubdate from titles) dt_e where pubdate = "450128 12:30:1PM" Here data from the SQL derived table dt_e is inserted into the new table pub_dates.CHAPTER 5 SQL Derived Tables Transact-SQL User’s Guide 165 Using views with SQL derived tables The following example creates a view, view_colo_publishers, using a SQL derived table, dt_colo_pubs, to display publishers based in Colorado: create view view_colo_publishers (Pub_Id, Publisher, City, State) as select pub_id, pub_name, city, state from (select * from publishers where state="CO") dt_colo_pubs Data can be inserted through a view that contains a SQL derived table if the insert rules and permission settings for the derived table expression follow the insert rules and permission settings for the select part of the create view statement. For example, the following insert statement inserts a row through the view_colo_publishers view into the publishers table on which the view is based: insert view_colo_publishers values (’1799’, ’Gigantico Publications’, ’Denver’, ’CO’) You can also update existing data through a view that uses a SQL derived table: update view_colo_publishers set Publisher = "Colossicorp Industries" where Pub_Id = "1699" Note You must specify the column names of the view definition, not the column names of the underlying table. Views that use a SQL derived table are dropped in the standard manner: drop view view_colo_publishers Correlated attributes Correlated attributes that exceed the scope of a SQL derived table cannot be referenced from a SQL derived table expression. For example, the following query will result in an error: select * from publishers where pub_id in (select pub_id from (select pub_id from titlesUsing SQL derived tables 166 Adaptive Server Enterprise where pub_id = publishers.pub_id) dt_publishers) Here, the column publishers.pub_id is referenced in the SQL derived table expression, but it is outside the scope of the SQL derived table dt_publishers.Transact-SQL User’s Guide 167 C H A P T E R 6 Joins: Retrieving Data from Several Tables A join operation compares two or more tables (or views) by specifying a column from each, comparing the values in those columns row by row, and linking the rows that have matching values. It then displays the results in a new table. The tables specified in the join can be in the same database or in different databases. This chapter discusses: You can state many joins as subqueries, which also involve two or more tables. See Chapter 4, “Subqueries: Using Queries Within Other Queries.” When Component Integration Services is enabled, you can perform joins across remote servers. For more information, see the Component Integration Services User’s Guide. Topic Page How joins work 168 How joins are structured 169 How joins are processed 174 Equijoins and natural joins 175 Joins with additional conditions 176 Joins not based on equality 177 Self-joins and correlation names 178 The not-equal join 179 Joining more than two tables 182 Outer joins 184 Transact-SQL outer joins 204 How null values affect joins 207 Determining which table columns to join 208How joins work 168 Adaptive Server Enterprise How joins work When you join two or more tables, the columns being compared must have similar values—that is, values using the same or similar datatypes. There are several types of joins, such as equijoins, natural joins, and outer joins. The most common join, the equijoin, is based on equality. The following join finds the names of authors and publishers located in the same city: select au_fname, au_lname, pub_name from authors, publishers where authors.city = publishers.city au_fname au_lname pub_name -------- -------- -------------------- Cheryl Carson Algodata Infosystems Abraham Bennet Algodata Infosystems (2 rows affected) Because the query draws on information contained in two separate tables, publishers and authors, you need a join to retrieve the requested information. This statement joins the publishers and authors tables using the city column as the link.: where authors.city = publishers.city Join syntax You can embed a join in a select, update, insert, delete, or subquery. Other join restrictions and clauses may follow the join conditions. Joins use the following syntax: start of select, update, insert, delete, or subquery from {table_list | view_list} where [not] [table_name. | view_name.]column_name join_operator [table_name. | view_name.]column_name [{and | or} [not] [table_name.|view_name.]column_name join_operator [table_name.|view_name.]column_name]... End of select, update, insert, delete, or subqueryCHAPTER 6 Joins: Retrieving Data from Several Tables Transact-SQL User’s Guide 169 Joins and the relational model The join operation is the hallmark of the relational model of database management. More than any other feature, the join distinguishes relational database management systems from other types of database management systems. In structured database management systems, often known as network and hierarchical systems, relationships between data values are predefined. Once a database has been set up, it is difficult to make queries about unanticipated relationships among the data. In a relational database management system, on the other hand, relationships among data values are left unstated in the definition of a database. They become explicit when the data is manipulated—when you query the database, not when you create it. You can ask any question that comes to mind about the data stored in the database, regardless of what was intended when the database was set up. According to the rules of good database design, called normalization rules, each table should describe one kind of entity—a person, place, event, or thing. That is why, when you want to compare information about two or more kinds of entities, you need the join operation. Relationships among data stored in different tables are discovered by joining them. A corollary of this rule is that the join operation gives you unlimited flexibility in adding new kinds of data to your database. You can always create a new table that contains data about a different kind of entity. If the new table has a field with values similar to those in some field of an existing table or tables, it can be linked to those other tables by joining. How joins are structured A join statement, like a select statement, starts with the keyword select. The columns named after the select keyword are the columns to be included in the query results, in their desired order. The previous example specified the columns that contained the authors’ names from the authors table, and publishers’ names from the publishers tables: select au_fname, au_lname, pub_name from authors, publishersHow joins are structured 170 Adaptive Server Enterprise You do not have to qualify the columns au_fname, au_lname, and pub_name by a table name because there is no ambiguity about the table to which they belong. But the city column used for the join comparison does need to be qualified, because there are columns of that name in both the authors and publishers tables: select au_fname, au_lname, pub_name from authors, publishers where authors.city = publishers.city Though neither of the city columns is printed in the results, Adaptive Server needs the table name to perform the comparison. To specify that all the columns of the tables involved in the query be included in the results, use an asterisk (*) with select. For example, to include all the columns in authors and publishers in the preceding join query, the statement is: select * from authors, publishers where authors.city = publishers.city au_id au_lname au_fname phone address city state postalcode contract pub_id pub_name city state ----------- -------- -------- ------------ --------------------- ---------- ----- ---------- -------- ------ -------------------- ---------- ----- 238-95-7766 Carson Cheryl 415 548-7723 589 Darwin Ln. Berkeley CA 94705 1 1389 Algodata Infosystems Berkeley CA 409-56-7008 Bennet Abraham 415 658-9932 223 Bateman St Berkeley CA 94705 1 1389 Algodata Infosystems Berkeley CA (2 rows affected) The display shows a total of 2 rows with 13 columns each. Because of the length of the rows, each takes up multiple horizontal lines in this display. Whenever “*” is used, the columns in the results are displayed in the order in which they were stated in the create statement that created the table. The select list and the results of a join need not include columns from both of the tables being joined. For example, to find the names of the authors that live in the same city as one of the publishers, your query need not include any columns from publishers: select au_lname, au_fname from authors, publishers where authors.city = publishers.city CHAPTER 6 Joins: Retrieving Data from Several Tables Transact-SQL User’s Guide 171 Remember, just as in any select statement, column names in the select list and table names in the from clause must be separated by commas. The from clause Use the from clause to specify which tables and views to join. This is the clause that indicates to Adaptive Server that a join is desired. You can list the tables or views in any order. The order of tables affects the results displayed only when you use select * to specify the select list. More than two tables or views can be named in the from clause. At most, a query can reference 16 tables. This maximum includes: • Base tables or views listed in the from clause • Each instance of multiple references to the same table (self-joins) • Tables referenced in subqueries • Base tables referenced by the views listed in the from clause • Tables being created with into • Work tables created as a result of the query If the join is part of an update or delete statement, the query can only refer to 15 tables. The following example joins columns from the titles and publishers tables, doubling the price of all books published in California: begin tran update titles set price = price * 2 from titles, publishers where titles.pub_id = publishers.pub_id and publishers.state = "CA" rollback tran See “Joining more than two tables” on page 182 for information on joins involving more than two tables or views. As explained in Chapter 2, “Queries: Selecting Data from a Table,” table or view names can be qualified by the names of the owner and database, and can be given correlation names for convenience. For example: select au_lname, au_fname from pubs2.blue.authors, pubs2.blue.publishers How joins are structured 172 Adaptive Server Enterprise where authors.city = publishers.city You can join views in exactly the same way as tables and use views wherever tables are used. Chapter 10, “Views: Limiting Access to Data” discusses views; this chapter uses only tables in its examples. The where clause Use the where clause to determine which rows are included in the results. where specifies the connection between the tables and views named in the from clause. Be sure to qualify column names if there is ambiguity about the table or view to which they belong. For example: where authors.city = publishers.city This where clause gives the names of the columns to be joined, qualified by table names if necessary, and the join operator—often equality, sometimes “greater than” or “less than.” For details of where clause syntax, see Chapter 2, “Queries: Selecting Data from a Table”. Note You will get unexpected results if you omit the where clause of a join. Without a where clause, any of the join queries discussed so far will produce 69 rows instead of 2. “How joins are processed” on page 174 explains this unexpected result. The where clause of a join statement can include other conditions in addition to the one that links columns from different tables. In other words, you can include a join operation and a select operation in the same SQL statement. See “How joins are processed” on page 174 for an example. Join operators Joins that match columns on the basis of equality are called equijoins. A more precise definition of an equijoin is given under “Equijoins and natural joins” on page 175, along with examples of joins not based on equality. Equijoins use the following comparison operators: CHAPTER 6 Joins: Retrieving Data from Several Tables Transact-SQL User’s Guide 173 Table 6-1: Join operators Joins that use the relational operators are collectively called theta joins. Another set of join operators is used for outer joins, also discussed in detail later in this chapter. The outer join operators are Transact-SQL extensions, as shown in Table 6-2: Table 6-2: Outer join operators Datatypes in join columns The columns being joined must have the same or compatible datatypes. Use the convert function when comparing columns whose datatypes cannot be implicitly converted. Columns being joined need not have the same name, although they often do. If the datatypes used in the join are compatible, Adaptive Server automatically converts them. For example, Adaptive Server converts among any of the numeric type columns—int, smallint, tinyint, decimal, or float, and among any of the character type and date columns—char, varchar, unichar, univarchar, nchar, nvarchar, datetime, date and time. For details on datatype conversion, see Chapter 11, “Using the Built-In Functions in Queries,” and the “Datatype Conversion Functions” section of the Reference Manual. Operator Meaning = Equal to > Greater than >= Greater than or equal to < Less than <= Less than or equal to != Not equal to !> Less than or equal to !< Greater than or equal to Operator Action *= Include in the results all the rows from the first table, not just the ones where the joined columns match. =* Include in the results all the rows from the second table, not just the ones where the joined columns match. How joins are processed 174 Adaptive Server Enterprise Joins and text and image columns You cannot use joins for columns containing text or image values. You can, however, compare the lengths of text columns from two tables with a where clause. For example: where datalength(textab_1.textcol) > datalength(textab_2.textcol) How joins are processed Knowing how joins are processed helps to understand them—and to figure out why, when you incorrectly state a join, you sometimes get unexpected results. This section describes the processing of joins in conceptual terms. Adaptive Server’s actual procedure is more sophisticated. Conceptually speaking, the first step in processing a join is to form the Cartesian product of the tables—all the possible combinations of the rows from each of the tables. The number of rows in a Cartesian product of two tables is equal to the number of rows in the first table multiplied by the number of rows in the second table. The Cartesian product of the authors table and the publishers table is 69 (23 authors multiplied by 3 publishers). You can have a look at a Cartesian product with any query that includes columns from more than one table in the select list, more than one table in the from clause, and no where clause. For example, if you leave the where clause off the join used in previous examples, Adaptive Server combines each of the 23 authors with each of the 3 publishers, and returns all 69 rows. This Cartesian product does not contain any particularly useful information. In fact, it is downright misleading, because it implies that every author in the database has a relationship with every publisher in the database—which is not true at all. That is why you must include a where clause in the join, which specifies the columns to be matched and the basis on which to match them. It may also include other restrictions. Once Adaptive Server forms the Cartesian product, it eliminates the rows that do not satisfy the join by using the conditions in the where clause. For example, the where clause in the previous example eliminates from the results all rows in which the author’s city is not the same as the publisher’s city:CHAPTER 6 Joins: Retrieving Data from Several Tables Transact-SQL User’s Guide 175 where authors.city = publishers.city Equijoins and natural joins Joins based on equality (=) are called equijoins. Equijoins compare the values in the columns being joined for equality and then include all the columns in the tables being joined in the results. This earlier query is an example of an equijoin: select * from authors, publishers where authors.city = publishers.city In the results of that statement, the city column appears twice. By definition, the results of an equijoin contain two identical columns. Because there is usually no point in repeating the same information, one of these columns can be eliminated by restating the query. The result is called a natural join. The query that results in the natural join of publishers and authors on the city column is: select publishers.pub_id, publishers.pub_name, publishers.state, authors.* from publishers, authors where publishers.city = authors.city The column publishers.city does not appear in the results. Another example of a natural join is: select au_fname, au_lname, pub_name from authors, publishers where authors.city = publishers.city You can use more than one join operator to join more than two tables or to join more than two pairs of columns. These “join expressions” are usually connected with and, although or is also legal. Following are two examples of joins connected by and. The first lists information about books (type of book, author, and title), ordered by book type. Books with more than one author have multiple listings, one for each author. select type, au_lname, au_fname, title from authors, titles, titleauthor where authors.au_id = titleauthor.au_id Joins with additional conditions 176 Adaptive Server Enterprise and titles.title_id = titleauthor.title_id order by type The second finds the names of authors and publishers that are located in the same city and state: select au_fname, au_lname, pub_name from authors, publishers where authors.city = publishers.city and authors.state = publishers.state Joins with additional conditions The where clause of a join query can include selection criteria as well as the join condition. For example, to retrieve the names and publishers of all the books for which advances of more than $7500 were paid, the statement is: select title, pub_name, advance from titles, publishers where titles.pub_id = publishers.pub_id and advance > $7500 title pub_name advance ----------------------------- -------------------- --------- You Can Combat Computer Stress! New Age Books 10,125.00 The Gourmet Microwave Binnet & Hardley 15,000.00 Secrets of Silicon Valley Algodata Infosystems 8,000.00 Sushi, Anyone? Binnet & Hardley 8,000.00 (4 rows affected) The columns being joined (pub_id from titles and publishers) do not need to appear in the select list and, therefore, do not show up in the results. You can include as many selection criteria as you want in a join statement. The order of the selection criteria and the join condition is not important.CHAPTER 6 Joins: Retrieving Data from Several Tables Transact-SQL User’s Guide 177 Joins not based on equality The condition for joining the values in two columns does not need to be equality. You can use any of the other comparison operators: not equal (!=), greater than (>), less than (<), greater than or equal to (>=), and less than or equal to (<=). Transact-SQL also provides the operators !> and !<, which are equivalent to <= and >=, respectively. This example of a greater-than join finds New Age authors who live in states that come after New Age Books’ state, Massachusetts, in alphabetical order. select pub_name, publishers.state, au_lname, au_fname, authors.state from publishers, authors where authors.state > publishers.state and pub_name = "New Age Books" pub_name state au_lname au_fname state ------------- ------ -------------- ----------- ----- New Age Books MA Greene Morningstar TN New Age Books MA Blotchet-Halls Reginald OR New Age Books MA del Castillo Innes MI New Age Books MA Panteley Sylvia MD New Age Books MA Ringer Anne UT New Age Books MA Ringer Albert UT (6 rows affected) The following example uses a >= join and a < join to look up the correct royalty from the roysched table, based on the book’s total sales. select t.title_id, t.total_sales, r.royalty from titles t, roysched r where t.title_id = r.title_id and t.total_sales >= r.lorange and t.total_sales < r.hirange title_id total_sales royalty -------- ----------- ------- BU1032 4095 10 BU1111 3876 10 BU2075 1872 24 BU7832 4095 10 MC2222 2032 12 MC3021 22246 24 PC1035 8780 16 PC8888 4095 10 PS1372 375 10 PS2091 2045 12 Self-joins and correlation names 178 Adaptive Server Enterprise PS2106 111 10 PS3333 4072 10 PS7777 3336 10 TC3218 375 10 TC4203 15096 14 TC7777 4095 10 (16 rows affected) Self-joins and correlation names Joins that compare values within the same column of one table are called selfjoins. To distinguish the two roles in which the table appears, use aliases, or correlation names. For example, you can use a self-join to find out which authors in Oakland, California, live in the same postal code area. Since this query involves a join of the authors table with itself, the authors table appears in two roles. To distinguish these roles, you can temporarily and arbitrarily give the authors table two different correlation names—such as au1 and au2—in the from clause. These correlation names qualify the column names in the rest of the query. The self-join statement looks like this: select au1.au_fname, au1.au_lname, au2.au_fname, au2.au_lname from authors au1, authors au2 where au1.city = "Oakland" and au2.city = "Oakland" and au1.state = "CA" and au2.state = "CA" and au1.postalcode = au2.postalcode au_fname au_lname au_fname au_lname --------- ----------- -------- -------- Marjorie Green Marjorie Green Dick Straight Dick Straight Dick Straight Dirk Stringer Dick Straight Livia Karsen Dirk Stringer Dick Straight Dirk Stringer Dirk Stringer Dirk Stringer Livia Karsen Stearns MacFeather Stearns MacFeather Livia Karsen Dick Straight Livia Karsen Dirk Stringer Livia Karsen Livia Karsen CHAPTER 6 Joins: Retrieving Data from Several Tables Transact-SQL User’s Guide 179 (11 rows affected) List the aliases in the from clause in the same order as you refer to them in the select list, as in this example. Depending on the query, the results may be ambiguous if you list them in a different order. To eliminate the rows in the results where the authors match themselves, and are identical except that the order of the authors is reversed, you can make this addition to the self-join query: select au1.au_fname, au1.au_lname, au2.au_fname, au2.au_lname from authors au1, authors au2 where au1.city = "Oakland" and au2.city = "Oakland" and au1.state = "CA" and au2.state = "CA" and au1.postalcode = au2.postalcode and au1.au_id < au2.au_id au_fname au_lname au_fname au_lname --------- ----------- --------- --------- Dick Straight Dirk Stringer Dick Straight Livia Karsen Dirk Stringer Livia Karsen (3 rows affected) It is now clear that Dick Straight, Dirk Stringer, and Livia Karsen all have the same postal code. The not-equal join The not-equal join is particularly useful in restricting the rows returned by a self-join. In the following example, a not-equal join and a self-join find the categories in which there are two or more inexpensive (less than $15) books of different prices: select distinct t1.type, t1.price from titles t1, titles t2 where t1.price < $15 and t2.price < $15 and t1.type = t2.type and t1.price != t2.price type price ---------- ----- business 2.99 The not-equal join 180 Adaptive Server Enterprise business 11.95 psychology 7.00 psychology 7.99 psychology 10.95 trad_cook 11.95 trad_cook 14.99 (7 rows affected) The expression “not column_name = column_name” is equivalent to “column_name != column_name.” The following example uses a not-equal join, combined with a self-join. It finds all the rows in the titleauthor table where there are two or more rows with the same title_id, but different au_id numbers that is, books which have more than one author. select distinct t1.au_id, t1.title_id from titleauthor t1, titleauthor t2 where t1.title_id = t2.title_id and t1.au_id != t2.au_id order by t1.title_id au_id title_id ----------- -------- 213-46-8915 BU1032 409-56-7008 BU1032 267-41-2394 BU1111 724-80-9391 BU1111 722-51-5454 MC3021 899-46-2035 MC3021 427-17-2319 PC8888 846-92-7186 PC8888 724-80-9391 PS1372 756-30-7391 PS1372 899-46-2035 PS2091 998-72-3567 PS2091 267-41-2394 TC7777 472-27-2349 TC7777 672-71-3249 TC7777 (15 rows affected) For each book in titles, the following example finds all other books of the same type that have a different price: select t1.type, t1.title_id, t1.price, t2.title_id, t2.price from titles t1, titles t2 CHAPTER 6 Joins: Retrieving Data from Several Tables Transact-SQL User’s Guide 181 where t1.type = t2.type and t1.price != t2.price Be careful when interpreting the results of a not-equal join. For example, it would be easy to think you could use a not-equal join to find the authors who live in a city where no publisher is located: select distinct au_lname, authors.city from publishers, authors where publishers.city != authors.city However, this query finds the authors who live in a city where no publishers are located, which is all of them. The correct SQL statement is a subquery: select distinct au_lname, authors.city from publishers, authors where authors.city not in (select city from publishers where authors.city = publishers.city) Not-equal joins and subqueries Sometimes a not-equal join query is not sufficiently restrictive and needs to be replaced by a subquery. For example, suppose you want to list the names of authors who live in a city where no publisher is located. For the sake of clarity, let us also restrict this query to authors whose last names begin with “A”, “B”, or “C”. A not-equal join query might be: select distinct au_lname, authors.city from publishers, authors where au_lname like "[ABC]%" and publishers.city != authors.city The results are not an answer to the question that was asked: au_lname city ---------------- ------------ Bennet Berkeley Carson Berkeley Blotchet-Halls Corvallis (3 rows affected) The system interprets this version of the SQL statement to mean: “find the names of authors who live in a city where some publisher is not located.” All the excluded authors qualify, including the authors who live in Berkeley, home of the publisher Algodata Infosystems. Joining more than two tables 182 Adaptive Server Enterprise In this case, the way that the system handles joins (first finding every eligible combination before evaluating other conditions) causes this query to return undesirable results. You must use a subquery to get the results you want. A subquery can eliminate the ineligible rows first and then perform the remaining restrictions. Here is the correct statement: select distinct au_lname, city from authors where au_lname like "[ABC]%" and city not in (select city from publishers where authors.city = publishers.city) Now, the results are what you want: au_lname city ------------- ------------ Blotchet-Halls Corvallis (1 row affected) Subqueries are covered in greater detail in Chapter 4, “Subqueries: Using Queries Within Other Queries.” Joining more than two tables The titleauthor table of pubs2 offers a good example of a situation in which joining more than two tables is helpful. To find the titles of all the books of a particular type and the names of their authors, the query is: select au_lname, au_fname, title from authors, titles, titleauthor where authors.au_id = titleauthor.au_id and titles.title_id = titleauthor.title_id and titles.type = "trad_cook" au_lname au_fname title -------------- ----------- ------------------------ Panteley Sylvia Onions, Leeks, and Garlic: Cooking Secrets of the Mediterranean Blotchet-Halls Reginald Fifty Years in Buckingham PalaceCHAPTER 6 Joins: Retrieving Data from Several Tables Transact-SQL User’s Guide 183 Kitchens O’Leary Michael Sushi, Anyone? Gringlesby Burt Sushi, Anyone? Yokomoto Akiko Sushi, Anyone? (5 rows affected) Notice that one of the tables in the from clause, titleauthor, does not contribute any columns to the results. Nor do any of the columns that are joined—au_id and title_id—appear in the results. Nonetheless, this join is possible only by using titleauthor as an intermediate table. You can also join more than two pairs of columns in the same statement. For example, here is a query that shows the title_id, its total sales and the range in which they fall, and the resulting royalty: select titles.title_id, total_sales, lorange, hirange, royalty from titles, roysched where titles.title_id = roysched.title_id and total_sales >= lorange and total_sales < hirange title_id total_sales lorange hirange royalty -------- ----------- ------- ------- ------- BU1032 4095 0 5000 10 BU1111 3876 0 4000 10 BU2075 18722 14001 50000 24 BU7832 4095 0 5000 10 MC2222 2032 2001 4000 12 MC3021 2224 12001 50000 24 PC1035 8780 4001 10000 16 PC8888 4095 0 5000 10 PS1372 375 0 10000 10 PS2091 2045 1001 5000 12 PS2106 111 0 2000 10 PS3333 4072 0 5000 10 PS7777 3336 0 5000 10 TC3218 375 0 2000 10 TC4203 15096 8001 16000 14 TC7777 4095 0 5000 10 (16 rows affected) When there is more than one join operator in the same statement, either to join more than two tables or to join more than two pairs of columns, the “join expressions” are almost always connected with and, as in the earlier examples. However, it is also legal to connect them with or. Outer joins 184 Adaptive Server Enterprise Outer joins Joins that include all rows, regardless of whether there is a matching row, are called outer joins. Adaptive Server supports both left and right outer joins. For example, the following query joins the titles and the titleauthor tables on their title_id column: select * from titles, titleauthor where titles.title_id *= titleauthor.title_id Sybase supports both Transact-SQL and ANSI outer joins. Transact-SQL outer joins (shown in the previous example) use the *= command to indicate a left outer join and the =* command to indicate a right outer join. Transact-SQL outer joins were created by Sybase as part of the Transact-SQL language. See “Transact-SQL outer joins” on page 204 for more information about TransactSQL outer joins. ANSI outer joins use the keywords left join and right join to indicate a left and right join, respectively. Sybase implemented the ANSI outer join syntax to fully comply with the ANSI standard. See “ANSI Inner and outer joins” on page 186 for more information about ANSI outer joins. This is the previous example rewritten as an ANSI outer join: select * from titles left join titleauthor on titles.title_id = titleauthor.title_id Inner and outer tables The terms outer table and inner table describe the placement of the tables in an outer join: • In a left join, the outer table and inner table are the left and right tables respectively. The outer table and inner table are also referred to as the rowpreserving and null-supplying tables, respectively. • In a right join, the outer table and inner table are the right and left tables respectively. For example, in the queries below, T1 is the outer table and T2 is the inner table: T1 left join T2 T2 right join T1 Or, using Transact-SQL syntax:CHAPTER 6 Joins: Retrieving Data from Several Tables Transact-SQL User’s Guide 185 T1 *= T2 T2 =* T1 Outer join restrictions If a table is an inner member of an outer join, it cannot participate in both an outer join clause and a regular join clause. The following query fails because the salesdetail table is part of both the outer join and a regular join clause: select distinct sales.stor_id, stor_name, title from sales, stores, titles, salesdetail where qty > 500 and salesdetail.title_id =* titles.title_id and sales.stor_id = salesdetail.stor_id and sales.stor_id = stores.stor_id Msg 303, Level 16, State 1: Server ’FUSSY’, Line 1: The table ’salesdetail’ is an inner member of an outerjoin clause. This is not allowed if the table also participates in a regular join clause. If you want to know the name of the store that sold more than 500 copies of a book, you would have to use a second query. If you submit a query with an outer join and a qualification on a column from the inner table of the outer join, the results may not be what you expect. The qualification in the query does not restrict the number of rows returned, but rather affects which rows contain the null value. For rows that do not meet the qualification, a null value appears in the inner table’s columns of those rows. Views used with outer joins If you define a view with an outer join, and then query the view with a qualification on a column from the inner table of the outer join, the results may not be what you expect. The query returns all rows from the inner table. Rows that do not meet the qualification show a NULL value in the appropriate columns of those rows. The following rules determine what types of updates you can make to columns through join views: • delete statements are not allowed on join views. • insert statements are not allowed on join views created with check option.Outer joins 186 Adaptive Server Enterprise • update statements are allowed on join views with check option. The update fails if any of the affected columns appears in the where clause, in an expression that includes columns from more than one table. • If you insert or update a row through a join view, all affected columns must belong to the same base table. ANSI Inner and outer joins This is the ANSI syntax for joining tables: left_table [inner | left [outer] | right [outer]] join right_table on left_column_name = right_column_name The result of the join between the left and the right tables is called a joined table. Joined tables are defined in the from clause. For example: select titles.title_id, title, ord_num, qty from titles left join salesdetail on titles.title_id = salesdetail.title_id title_id title ord_num qty ----------------------------- -------------------- --- -- BU1032 The Busy Executive AX-532-FED-452-2Z7 200 BU1032 The Busy Executive NF-123-ADS-642-9G3 1000 . . . TC7777 Sushi, Anyone? ZD-123-DFG-752-9G8 1500 TC7777 Sushi, Anyone? XS-135-DER-432-8J2 1090 (118 rows affected) ANSI join syntax allows you to write either: • Inner joins, in which the joined table includes only the rows of the inner and outer tables that meet the conditions of the on clause. For information, see “ANSI inner joins” on page 189. The result set of a query that includes an inner join does not include any null-supplied rows for the rows of the outer table that do not meet the conditions of the on clause.CHAPTER 6 Joins: Retrieving Data from Several Tables Transact-SQL User’s Guide 187 • Outer joins, in which the joined table includes all the rows from the outer table whether or not they meet the conditions of the on clause. If a row does not meet the conditions of the on clause, values from the inner table are stored in the joined table as null values. The where clause of an ANSI outer join restricts the rows that are included in the query result. For more information, see “ANSI outer joins” on page 192. Note You can also use ANSI syntax to join views. Sybase ANSI join syntax does not support the using clause. Correlation name and column referencing rules for ANSI joins The following are the correlation name and column reference rules specifically for ANSI joins. For more information about correlation names, see “Self-joins and correlation names” on page 178. • If a table or view uses a correlation name reference to the column or view it must always use the same correlation name, rather than the table name or view name. That is, you cannot name a table in a query with a correlation name and then use its table name later. The following example correctly uses the correlation name t to specify the table where its pub_id column is specified: select title, t.pub_id, pub_name from titles t left join publishers p on t.pub_id = p.pub_id However, the following example incorrectly uses the table name instead of the correlation name for the titles table (t.pub_id) in the on clause of the query and produces the subsequent error message: select title, t.pub_id, pub_name from titles t left join publishers p on titles.pub_id = p.pub_id Msg 107, Level 15, State 1: Server ‘server_name’, Line 1: The column prefix ‘t’ does not match with a table name or alias name used in the query. Either the table is not specified in the FROM clause or it has a correlation name which must be used instead. • The restriction specified in the on clause can reference: • Columns that are specified in the joined table’s referenceOuter joins 188 Adaptive Server Enterprise • Columns that are specified in joined tables that are contained in the ANSI join (for example, in a nested join) • Correlation names in subqueries for tables specified in outer query blocks • The condition specified in the on clause cannot reference columns that are introduced in ANSI joins that contain another ANSI join (typically when the joined table produced by the second join is joined with the first join). Here is an example of an illegal column reference that produces an error: select * from titles left join titleauthor on titles.title_id=roysched.title_id /*join #1*/ left join roysched on titleauthor.title_id=roysched.title_id /*join #2*/ where titles.title_id != "PS7777" The first left join cannot reference the roysched.title_id column because this column is not introduced until the second join. You can correctly rewrite this query as: select * from titles left join (titleauthor left join roysched on titleauthor.title_id = roysched.title_id) /*join #1*/ on titles.title_id = roysched.title_id /*join #2*/ where titles.title_id != "PS7777" And another example: select title, price, titleauthor.au_id, titleauthor.title_id, pub_name, publishers.city from roysched, titles left join titleauthor on roysched.title_id=titleauthor.title_id left join authors on titleauthor.au_id=roysched.au_id, publishers In this query, neither the roysched table or the publishers table are part of either left join. Because of this, neither left join can refer to columns in either the roysched or publishers tables as part of their on clause condition.CHAPTER 6 Joins: Retrieving Data from Several Tables Transact-SQL User’s Guide 189 ANSI inner joins Joins that produce a result set that includes only the rows of the joining tables that meet the restriction are called inner joins. Rows that do not meet the join restriction are not included in the joined table. If you require the joined table to include all the rows from one of the tables, regardless of whether they meet the restriction, use an outer join. See “ANSI outer joins” on page 192, for more information. Adaptive Server supports the use of both Transact-SQL inner joins and ANSI inner joins. Queries using Transact-SQL inner joins separate the tables being joined by commas and list the join comparisons and restrictions in the where clause. For example: select au_id, titles.title_id, title, price from titleauthor, titles where titleauthor.title_id = titles.title_id and price > $15 For information about writing Transact-SQL inner joins, see “How joins are structured” on page 169. ANSI-standard inner joins syntax is: select select_list from table1 inner join table2 on join_condition For example, the following use of inner join is equivalent to the Transact SQL join above: select au_id, titles.title_id, title, price from titleauthor inner join titles on titleauthor.title_id = titles.title_id and price > 15 au_id title_id title price ---------- -------- ------------------------ -- --- 213-46-8915 BU1032 The Busy Executive’s Datab 19.99 409-56-7008 BU1032 The Busy Executive’s Datab 19.99 . . . 172-32-1176 PS3333 Prolonged Data Deprivation 19.99 807-91-6654 TC3218 Onions, Leeks, and Garlic: 20.95 (11 rows affected) The two methods of writing joins, ANSI or Transact-SQL, are equivalent. For example, there is no difference between the result sets produced by the following queries:Outer joins 190 Adaptive Server Enterprise select title_id, pub_name from titles, publishers where titles.pub_id = publishers.pub_id and select title_id, pub_name from titles left join publishers on titles.pub_id = publishers.pub_id An inner join can be part of an update or delete statement. For example, the following query multiplies the price for all the titles published in California by 1.25: begin tran update titles set price = price * 1.25 from titles inner join publishers on titles.pub_id = publishers.pub_id and publishers.state = "CA" The join table of an inner join An ANSI join specifies which tables or views to join in the query. The table references specified in the ANSI join comprise the joined table. For example, the join table of the following query includes the title, price, advance, and royaltyper columns: select title, price, advance, royaltyper from titles inner join titleauthor on titles.title_id = titleauthor.title_id title price advance royaltyper ----------- ------- ---------- ---------- The Busy... 19.99 5,000.00 40 The Busy... 19.99 5,000.00 60 . . . Sushi, A... 14.99 8,000.00 30 Sushi, A... 14.99 8,000.00 40 (25 rows affected) If a joined table is used as a table reference in an ANSI inner join, it becomes a nested inner join. ANSI nested inner joins follow the same rules as ANSI outer joins. A query can reference a maximum of 50 user tables (or 14 work tables) on each side of a union, including: • Base tables or views listed in the from clauseCHAPTER 6 Joins: Retrieving Data from Several Tables Transact-SQL User’s Guide 191 • Each correlated reference to the same table (self-join) • Tables referenced in subqueries • Base tables referenced by the views or nested views • Tables being created with into The on clause of an ANSI inner join The on clause of an ANSI inner join specifies the conditions used when the tables or views are joined. Although you can join on any column of a table, your performance may be better if these columns are indexed. Often, you must use qualifiers (table or correlation names) to uniquely identify the columns and the tables to which they belong. For example: from titles t left join titleauthor ta on t.title_id = ta.title_id This on clause eliminates rows from both tables where there is no matching title_id. For more information about correlation names, see “Self-joins and correlation names” on page 178. The on clause often compares the ANSI joins tables, as in the third and fourth line of the following query: select title, price, pub_name from titles inner join publishers on titles.pub_id = publishers.pub_id and total_sales > 300 The join restriction specified in this on clause removes all rows from the join table that do not have sales greater than 300. The on clause can also specify search arguments, as illustrated in the fourth line of the query. ANSI inner joins restrict the result set similarly whether the condition is placed in the on clause or the where clause (unless they are nested in an outer join). That is, the following queries produce the same result sets: select stor_name, stor_address, ord_num, qty from salesdetail inner join stores on salesdetail.stor_id = stores.stor_id where qty > 3000 and select stor_name, stor_address, ord_num, qty from salesdetail inner join stores on salesdetail.stor_id = stores.stor_id and qty > 3000Outer joins 192 Adaptive Server Enterprise A query is usually more readable if the restriction is placed in the where clause; this explicitly tells users which rows of the join table are included in the result set. ANSI outer joins Joins that produce a joined table that includes all rows from the outer table, regardless of whether the on clause produces matching rows or not, are called outer joins. Inner joins and equijoins produce a result set that includes only the rows from the tables where there are matching values in the join clause. There are times, however, when you want to include not only the matching rows, but also the rows from one of the tables where there are no matching rows in the second table. This type of join is an outer join. In an outer join, rows that do not meet the on clause conditions are included in the joined table with nullsupplied values for the inner table of the outer join. The inner table is also referred to as the null-supplying member. The roles of the inner and outer tables are described in Figure 4-1:CHAPTER 6 Joins: Retrieving Data from Several Tables Transact-SQL User’s Guide 193 Figure 6-1: The roles of an outer and inner table in an outer join Sybase recommends that applications use ANSI outer joins because they unambiguously specify whether the on or where clause contains the predicate. This section discusses only the ANSI outer joins; for information about Transact-SQL outer joins, see “Transact-SQL outer joins” on page 204. Note Queries that contain ANSI outer joins cannot contain Transact-SQL outer joins, and vice versa. However, a query with ANSI outer joins can reference a view that contains a Transact-SQL outer join, and vice versa. ANSI outer join syntax is: select select_list from table1 {left | right} [outer] join table2 on predicate [join restriction]Outer joins 194 Adaptive Server Enterprise Left joins retain all the rows of the table reference listed on the left of the join clause; right joins retain all the rows of the table reference on the right of the join clause. In left joins, the left table reference is referred to as the outer table or row-preserving table. The following example determines the authors who live in the same city as their publishers: select au_fname, au_lname, pub_name from authors left join publishers on authors.city = publishers.city au_fname au_lname pub_name --------- ---------- ------------- Johnson White NULL Marjorie Green NULL Cheryl Carson Algodata Infosystems . . . Abraham Bennet Algodata Infosystems . . . Anne Ringer NULL Albert Ringer NULL (23 rows affected) The result set contains all the authors from the authors table. The authors who do not live in the same city as their publishers produce null values in the pub_name column. Only the authors who live in the same city as their publishers, Cheryl Carson and Abraham Bennet, produce a non-null value in the pub_name column. You can rewrite a left outer join as a right outer join by reversing the placement of the tables in the from clause. Also, if the select statement specifies “select *”, you must write an explicit list of all the column names, otherwise the columns in the result set may not be in the same order for the rewritten query. Here is the previous example rewritten as a right outer join, which produces the same result set as the left outer join above: select au_fname, au_lname, pub_name from publishers right join authors on authors.city = publishers.cityCHAPTER 6 Joins: Retrieving Data from Several Tables Transact-SQL User’s Guide 195 Should the predicate be in the on or where clause? The result set of an ANSI outer join depends on whether you place the restriction in the on or the where clause. The on clause defines the result set of a joined table and which rows of this joined table have null-supplied values; the where clause defines which rows of the joined table are included in the result set. Whether you use an on or a where clause in your join condition depends on what you want your result set to include. The following examples may help you decide whether to place the predicate in the on or the where clause. Predicate restrictions on an outer table The following query places a restriction on the outer table in the where clause. Because the restriction is applied to the result of the outer join, it removes all the rows for which the condition is not true: select title, titles.title_id, price, au_id from titles left join titleauthor on titles.title_id = titleauthor.title_id where titles.price > $20.00 title title_id price au_id ------------------- -------- ---------- ----------------- But Is It User F... PC1035 22.95 238-95-7766 Computer Phobic ... PS1372 21.59 724-80-9391 Computer Phobic ... PS1372 21.59 756-30-7391 Onions, Leeks, a... TC3218 20.95 807-91-6654 (4 rows affected) Four rows meet the criteria and only these are included in the result set. However, if you move this restriction on the outer table to the on clause, the result set includes all the rows that meet the on clause condition. Rows from the outer table that do not meet the condition are null-extended: select title, titles.title_id, price, au_id from titles left join titleauthor on titles.title_id = titleauthor.title_id and titles.price > $20.00 title title_id price au_id -------------------- --------- ------ --------------- The Busy Executive’s BU1032 19.99 NULL Cooking with Compute BU1111 11.95 NULL You Can Combat Compu BU2075 2.99 NULL Straight Talk About BU7832 19.99 NULL Silicon Valley Gastro MC2222 19.99 NULL The Gourmet Microwave MC3021 2.99 NULL The Psychology of Com MC3026 NULL NULL But Is It User Friend PC1035 22.95 238-95-7766Outer joins 196 Adaptive Server Enterprise Secrets of Silicon Va PC8888 20.00 NULL Net Etiquette PC9999 NULL NULL Computer Phobic and PS1372 21.59 724-80-9391 Computer Phobic and PS1372 21.59 756-30-7391 Is Anger the Enemy? PS2091 10.95 NULL Life Without Fear PS2106 7.00 NULL Prolonged Data Depri PS3333 19.99 NULL Emotional Security: PS7777 7.99 NULL Onions, Leeks, and Ga TC3218 20.95 807-91-6654 Fifty Years in Buckin TC4203 11.95 NULL Sushi, Anyone? TC7777 14.99 NULL (19 rows affected) Moving the restriction to the on clause added 15 null-supplied rows to the result set. Generally, if your query uses a restriction on an outer table, and you want the result set to remove only the rows for which the restriction is false, you should probably place the restriction in the where clause to limit the rows of the result set. Outer table predicates are not used for index keys if they are in the on clause. Whether you place the restriction on an outer table in the on or where clause ultimately depends on the information you need the query to return. If you only want the result set to include only the rows for which the restriction is true, you should place the restriction in the where clause. However if you require the result set to include all the rows of the outer table, regardless of whether they satisfy the restriction, you should place the restriction in the on clause. Restrictions on an inner table The following query includes a restriction on an inner table in the where clause: select title, titles.title_id, titles.price, au_id from titleauthor left join titles on titles.title_id = titleauthor.title_id where titles.price > $20.00 title title_id price au_id ------------- -------- ----- ----------- But Is It U... PC1035 22.95 238-95-7766 Computer Ph... PS1372 21.59 724-80-9391 Computer Ph... PS1372 21.59 756-30-7391 Onions, Lee... TC3218 20.95 807-91-6654 (4 rows affected)CHAPTER 6 Joins: Retrieving Data from Several Tables Transact-SQL User’s Guide 197 Because the restriction of the where clause is applied to the result set after the join is made, it removes all the rows for which the restriction is not true. Put another way, the where clause is not true for all null-supplied values and removes them. A join that places its restriction in the where clause is effectively an inner join. However, if you move the restriction to the on clause, it is applied during the join and is utilized in the production of the joined table. In this case, the result set includes all the rows of the inner table for which the restriction is true, plus all the rows of the outer table, which are null-extended if they do not meet the restriction criteria: select title, titles.title_id, price, au_id from titleauthor left join titles on titles.title_id = titleauthor.title_id and price > $20.00 title title_id price au_id --------- --------- ----------- ----------- NULL NULL NULL 172-32-1176 NULL NULL NULL 213-46-8915 . . . Onions, TC3218 20.95 807-91-6654 . . . NUL NULL NULL 998-72-3567 NULL NULL NULL 998-72-3567 (25 rows affected) This result set includes 21 rows that the previous example did not include. Generally, if your query requires a restriction on an inner table (for example “and price > $20.00” in query above), you probably want to place the condition in the on clause; this preserves the rows of the outer table. If you include a restriction for an inner table in the where clause, the result set might not include the rows of the outer table. Like the criteria for the placement of a restriction on an outer table, whether you place the restriction for an inner table in the on or where clause ultimately depends on the result set you want. If you are interested only in the rows for which the restriction is true, and not including the full set of rows for the outer table, place the restriction in the where clause. However, if you require the result set to include all the rows of the outer table, regardless of whether they satisfy the restriction, you should place the restriction in the on clause. Restrictions included in both an inner and outer table The restriction in the where clause of the following query includes both the inner and outer tables: select title, titles.title_id, price, price*qty, qty Outer joins 198 Adaptive Server Enterprise from salesdetail left join titles on titles.title_id = salesdetail.title_id where price*qty > $30000.00 title title_id price qty ----------------- -------- ----- --------- ----- Silicon Valley Ga MC2222 19.99 40,619.68 2032 But Is It User Fr PC1035 22.95 45,900.00 2000 But Is It User Fr PC1035 22.95 45,900.00 2000 But Is It User Fr PC1035 22.95 49,067.10 2138 Secrets of Silico PC8888 20.00 40,000.00 2000 Prolonged Data De PS3333 19.99 53,713.13 2687 Fifty Years in Bu TC4203 11.95 32,265.00 2700 Fifty Years in Bu TC4203 11.95 41,825.00 3500 (8 rows affected) Placing the restriction in the where clause eliminates the following rows from the result set: • The rows for which the restriction “price*qty>$30000.0” is false • The rows for which the restriction “price*qty>$30000.0” is unknown because price is null To keep the unmatched rows of the outer table, move the restriction into the on clause, as in this example: select title, titles.title_id, price, price*qty, qty from salesdetail left join titles on titles.title_id = salesdetail.title_id and price*qty > $30000.00 title title_id price qty ----------------- -------- ----- --------- ----- NULL NULL NULL NULL 75 NULL NULL NULL NULL 75 . . . Secrets of Silico PC8888 20.00 40,000.00 2000 . . . NULL NULL NULL NULL 300 NULL NULL NULL NULL 400 (116 rows affected) This query retains all 116 rows of the salesdetail table in the result set, and nullextends the rows that do not meet the restriction.CHAPTER 6 Joins: Retrieving Data from Several Tables Transact-SQL User’s Guide 199 Where you place the restriction that includes both the inner and outer table depends on the result set you want. If you are interested in only the rows for which the restriction is true, place the restriction in the where clause. However, if you want to include all the rows of the outer table, regardless of whether they satisfy the restriction, place the restriction in the on clause. Nested ANSI outer joins Nested outer joins use the result set of one outer join as the table reference for another. For example: select t.title_id, title, ord_num, sd.stor_id, stor_name from (salesdetail sd left join titles t on sd.title_id = t.title_id) /*join #1*/ left join stores on sd.stor_id = stores.stor_id /*join #2*/ title_id title ord_num stor_id stor_name -------- ------------ ------- ------- ------------------------ TC3218 Onions, L... 234518 7896 Fricative Bookshop TC7777 Sushi, An... 234518 7896 Fricative Bookshop . . . TC4203 Fifty Yea... 234518 6380 Eric the Read Books MC3021 The Gourmet... 234518 6380 Eric the Read Books (116 rows affected) In this example, the joined table between the salesdetail and titles tables is logically produced first and is then joined with the columns of the stores table where salesdetail.stor_id equals stores.stor_id. Semantically, each level of nesting in a join creates a joined table and is then used for the next join. In the query above, because the first outer join becomes an operator of the second outer join, this query is a left-nested outer join. This example shows a right nested outer join: select stor_name, qty, date, sd.ord_num from salesdetail sd left join (stores /*join #1 */ left join sales on stores.stor_id = sales.stor_id) /*join #2 */ on stores.stor_id = sd.stor_id where date > "1/1/1990" stor_name qty date ord_num ------------ ---- ------------------ -------------------- News & Brews 200 Jun 13 1990 12:00AM NB-3.142 News & Brews 250 Jun 13 1990 12:00AM NB-3.142 News & Brews 345 Jun 13 1990 12:00AM NB-3.142 . . .Outer joins 200 Adaptive Server Enterprise Thoreau Read 1005 Mar 21 1991 12:00AM ZZ-999-ZZZ-999-0A0 Thoreau Read 2500 Mar 21 1991 12:00AM AB-123-DEF-425-1Z3 Thoreau Read 4000 Mar 21 1991 12:00AM AB-123-DEF-425-1Z3 In this example, the second join (between the stores and the sales tables) is logically produced first, and is joined with the salesdetail table. Because the second outer join is used as the table reference for the first outer join, this query is a right-nested outer join. If the on clause for the first outer join (“from salesdetail. . .”) fails, it supplies null values to both the stores and sales tables in the second outer join. Parentheses in nested outer joins Nested outer joins produce the same result set with or without parenthesis. Large queries with many outer joins can be much more readable for users if the joins are structured using parentheses. The on clause in nested outer joins The placement of the on clause in a nested outer join determines which join is logically processed first. Reading from left to right, the first on clause is the first join to be defined. In this example, the position of the on clause in the first join (in parentheses indicates that it is the table reference for the second join, so it is defined first, producing the table reference to be joined with the authors table: select title, price, au_fname, au_lname from (titles left join titleauthor on titles.title_id = titleauthor.title_id) /*join #1*/ left join authors on titleauthor.au_id = authors.au_id /*join #2*/ and titles.price > $15.00 title price au_fname au_lname --------------- --------- ------------ ------------- The Busy Exe... 19.99 Marjorie Green The Busy Exe... 19.99 Abrahame Bennet . . . Sushi, Anyon... 14.99 Burt Gringlesby Sushi, Anyon... 14.99 Akiko Yokomoto (26 rows affected) However, if the on clauses are in different locations, the joins are evaluated in a different sequence, but still produce the same result set (this is for explanatory purposes only; if joined tables are logically produced in a different order, it is highly unlikely that they will produce the same result set):CHAPTER 6 Joins: Retrieving Data from Several Tables Transact-SQL User’s Guide 201 select title, price, au_fname, au_lname from titles left join (titleauthor left join authors on titleauthor.au_id = authors.au_id) /*join #2*/ on titles.title_id = titleauthor.title_id /*join #1*/ and au_lname like “Yokomoto” title price au_fname au_lname ---------------------- ------- ----------- ----------- The Busy Executive’s 19.99 Marjorie Green The Busy Executive’s 19.99 Abraham Bennet . . . Sushi, Anyone? 14.99 Burt Gringlesby Sushi, Anyone? 14.99 Akiko Yokomoto (26 rows affected) The position of the on clause of the first join (the last line of the query) indicates that the second left join is a table reference of the first join, so it is performed first. That is, the result of the second left join is joined with the titles table. Converting outer joins with join-order dependency Almost all Transact-SQL outer joins written for earlier versions of Adaptive Server that are run on a version 12.0 and later Adaptive Server produce the same result set. However, there is a category of outer join queries whose result sets depend on the join order chosen during optimization. Depending on where in the query the predicate is evaluated, these queries may produce different result sets when they are issued using the current version of Adaptive Server. The result sets they return are determined by the ANSI rules for assigning predicates to joins. Predicates cannot be evaluated until all the tables they reference are processed. That is, in the following query the predicate “and titles.price > 20” cannot be evaluated until the titles table is processed: select title, price, au_ord from titles, titleauthor where titles.title_id *= titleauthor.title_id and titles.price > 20 Predicates in earlier versions of Adaptive Server were evaluated according to the following semantics:Outer joins 202 Adaptive Server Enterprise • If the predicate was evaluated on the inner table of an outer join, the predicate had on clause semantics. • If the predicate was evaluated with a table that is outer to all outer joins, or is join-order independent, the predicate had where clause semantics. Note Before you run Adaptive Server in a production environment, make sure you start it with traceflag 4413 and run any queries that you think may be join-order dependent in pre-12.0 versions of Adaptive Server. Adaptive Server started with trace flag 4413 issues a message similar to the following when you run a query that is join-order dependent in a pre-12.0 version of Adaptive Server: Warning: The results of the statement on line %d are join-order independent. Results may differ on pre- 12.0 releases, where the query is potentially joinorder dependent. Make sure you resolve dependencies your applications have on result sets of join-order queries produced by pre-12.0 Adaptive Server. When do join-order dependent outer joins affect me? Generally, you will not have any problem from join-order dependent queries because predicates typically only reference: • An outer table, which is evaluated using where clause semantics • An inner table, which is evaluated using on clause semantics • The inner table and tables upon which the inner table is dependent These do not produce join-order dependent outer joins. However, TransactSQL queries that have any of the following characteristics may produce a different result set after they are translated to an ANSI outer join: • Predicates that contain or statements and reference an inner table of an outer join and another table that this inner table is not dependent on • Inner table attributes that are referenced in the same predicate as a table which is not in the inner table’s join-order dependency • An inner table referenced in a subquery as a correlated reference The following examples demonstrate the issues of translating Transact-SQL queries with join-order dependency to ANSI outer join queries. Example:CHAPTER 6 Joins: Retrieving Data from Several Tables Transact-SQL User’s Guide 203 select title, price, authors.au_id, au_lname from titles, titleauthor, authors where titles.title_id =* titleauthor.title_id and titleauthor.au_id = authors.au_id and (titles.price is null or authors.postalcode = ’94001’) This query is join-order independent because the outer join references both the titleauthor and the titles tables, and the authors table can be joined with these tables according to three join orders: • authors, titleauthors, titles (as part of the on clause) • titleauthors, authors, titles (as part of the on clause) • titleauthors, titles, authors (as part of the where clause) This query produces the following message: Warning: The results of the statement on line 1 are join-order independent. Results may differ on pre-12.0 releases, where the query is potentially joinorder dependent. Use trace flag 4413 to suppress this warning message. Following is the ANSI equivalent: select title, price, authors.au_id, au_lname from titles right join (titleauthor inner join authors on titleauthor.au_id = authors.au_id) on titles.title_id = titleauthor.title_id where (titles.price is null or authors.postalcode = ’94001’) Another example: select title, au_fname, au_lname, titleauthor.au_id, price from titles, titleauthor, authors where authors.au_id *= titleauthor.au_id and titleauthor.au_ord*titles.price > 40 The query is join-order dependent for the same reason as the previous example. Here is the ANSI equivalent: select title, au_fname, au_lname, titleauthor.au_id, price from titles,(authors left join titleauthor on titleauthor.au_id = authors.au_id) where titleauthor.au_ord*titles.price > 40Outer joins 204 Adaptive Server Enterprise Transact-SQL outer joins Transact-SQL includes syntax for both left and right outer joins. The left outer join, *=, selects all rows from the first table that meet the statement’s restrictions. The second table generates values if there is a match on the join condition. Otherwise, the second table generates null values. For example, the following left outer join lists all authors and finds the publishers (if any) in their city: select au_fname, au_lname, pub_name from authors, publishers where authors.city *= publishers.city The right outer join, =*, selects all rows from the second table that meet the statement’s restrictions. The first table generates values if there is a match on the join condition. Otherwise, the first table generates null values. Note You cannot include a Transact-SQL outer join in a having clause. A table is either an inner or an outer member of an outer join. If the join operator is *=, the second table is the inner table; if the join operator is =*, the first table is the inner table. You can compare a column from the inner table to a constant as well as using it in the outer join. For example, if you want to find out which title has sold more than 4000 copies: select qty, title from salesdetail, titles where qty > 4000 and titles.title_id *= salesdetail.title_id However, the inner table in an outer join cannot also participate in a regular join clause. An earlier example used a join to find the names of authors who live in the same city as a publisher returned two names: Abraham Bennet and Cheryl Carson. To include all the authors in the results, regardless of whether a publisher is located in the same city, use an outer join. Here is what the query and the results of the outer join look like: select au_fname, au_lname, pub_name from authors, publishers where authors.city *= publishers.city au_fname au_lname pub_name --------- -------------- --------------- Johnson White NULL Marjorie Green NULL Cheryl Carson Algodata Infosystems CHAPTER 6 Joins: Retrieving Data from Several Tables Transact-SQL User’s Guide 205 Michael O’Leary NULL Dick Straight NULL Meander Smith NULL Abraham Bennet Algodata Infosystems Ann Dull NULL Burt Gringlesby NULL Chastity Locksley NULL Morningstar Greene NULL Reginald Blotche-Halls NULL Akiko Yokomoto NULL Innes del Castillo NULL Michel DeFrance NULL Dirk Stringer NULL Stearns MacFeather NULL Livia Karsen NULL Sylvia Panteley NULL Sheryl Hunter NULL Heather McBadden NULL Anne Ringer NULL Albert Ringer NULL (23 rows affected) The comparison operator *= distinguishes the outer join from an ordinary join. This “left” outer join tells Adaptive Server to include all the rows in the authors table in the results, whether or not there is a match on the city column in the publishers table. Notice that in the results, there is no matching data for most of the authors listed, so these rows contain NULL in the pub_name column. The “right” outer join is specified with the comparison operator =*, which indicates that all the rows in the second table are to be included in the results, regardless of whether there is matching data in the first table. Substituting this operator in the outer join query shown earlier gives this result: select au_fname, au_lname, pub_name from authors, publishers where authors.city =* publishers.city au_fname au_lname pub_name --------- --------- --------------- NULL NULL New Age Books NULL NULL Binnet & Hardley Cheryl Carson Algodata Infosystems Abraham Bennet Algodata Infosystems (4 rows affected) Outer joins 206 Adaptive Server Enterprise You can further restrict an outer join by comparing it to a constant. This means that you can zoom in on precisely the values you really want to see and use the outer join to list the rows that did not make the cut. Let us look at the equijoin first and compare it to the outer join. For example, to find out which titles had a sale of more than 500 copies from any store, use this query: select distinct salesdetail.stor_id, title from titles, salesdetail where qty > 500 and salesdetail.title_id = titles.title_id stor_id title ------- -------------------------------------------- 5023 Sushi, Anyone? 5023 Is Anger the Enemy? 5023 The Gourmet Microwave 5023 But Is It User Friendly? 5023 Secrets of Silicon Valley 5023 Straight Talk About Computers 5023 You Can Combat Computer Stress! 5023 Silicon Valley Gastronomic Treats 5023 Emotional Security: A New Algorithm 5023 The Busy Executive’s Database Guide 5023 Fifty Years in Buckingham Palace Kitchens 5023 Prolonged Data Deprivation: Four Case Studies 5023 Cooking with Computers: Surreptitious Balance Sheets 7067 Fifty Years in Buckingham Palace Kitchens (14 rows affected) Also, to show the titles that did not have a sale of more than 500 copies in any store, you can use an outer join query: select distinct salesdetail.stor_id, title from titles, salesdetail where qty > 500 and salesdetail.title_id =* titles.title_id stor_id title ------- ------------------------------------------- NULL Net Etiquette NULL Life Without Fear 5023 Sushi, Anyone? 5023 Is Anger the Enemy? 5023 The Gourmet Microwave 5023 But Is It User Friendly? 5023 Secrets of Silicon Valley 5023 Straight Talk About Computers NULL The Psychology of Computer Cooking CHAPTER 6 Joins: Retrieving Data from Several Tables Transact-SQL User’s Guide 207 5023 You Can Combat Computer Stress! 5023 Silicon Valley Gastronomic Treats 5023 Emotional Security: A New Algorithm 5023 The Busy Executive’s Database Guide 5023 Fifty Years in Buckingham Palace Kitchens 7067 Fifty Years in Buckingham Palace Kitchens 5023 Prolonged Data Deprivation: Four Case Studies 5023 Cooking with Computers: Surreptitious Balance Sheets NULL Computer Phobic and Non-Phobic Individuals: Behavior Variations NULL Onions, Leeks, and Garlic: Cooking Secrets of the Mediterranean (19 rows affected) You can restrict an inner table with a simple clause. The following example lists the authors who live in the same city as a publisher, but excludes the author Cheryl Carson, who would normally be listed as an author living in a publisher’s city: select au_fname, au_lname, pub_name from authors, publishers where authors.city =* publishers.city and authors.au_lname != "Carson" au_fname au_lname pub_name --------- --------- --------------- NULL NULL New Age Books NULL NULL Binnet & Hardley Abraham Bennet Algodata Infosystems (3 rows affected) How null values affect joins Null values in tables or views being joined will never match each other. Since bit columns do not permit null values, a value of 0 appears in an outer join when there is no match for a bit column that is in the inner table. The result of a join of NULL with any other value is NULL. Because null values represent unknown or inapplicable values, Transact-SQL has no reason to believe that one unknown value matches another. Determining which table columns to join 208 Adaptive Server Enterprise You can detect the presence of null values in a column from one of the tables being joined only by using an outer join. Here are two tables, each of which has a NULL in the column that will participate in the join. A left outer join displays the null value in the first table. Figure 6-2: Null values in outer join Here is the left outer join: select * from t1, t2 where a *= c a b c d ----------- ------ ----------- ------ 1 one NULL NULL NULL three NULL NULL 4 join4 4 four (3 rows affected) The results make it difficult to distinguish a null in the data from a null that represents a failure to join. When null values are present in data being joined, it is usually preferable to omit them from the results by using a regular join. Determining which table columns to join sp_helpjoins lists the columns in two tables or views that are likely join candidates. Its syntax is: sp_helpjoins table1, table2CHAPTER 6 Joins: Retrieving Data from Several Tables Transact-SQL User’s Guide 209 For example, here is how to use sp_helpjoins to find the likely join columns between titleauthor and titles: sp_helpjoins titleauthor, titles first_pair ----------------------------- -------------------- title_id title_id The column pairs that sp_helpjoins displays come from two sources. First, sp_helpjoins checks the syskeys table in the current database to see if any foreign keys have been defined on the two tables with sp_foreignkey, and then checks to see if any common keys have been defined on the two tables with sp_commonkey. If it does not find any common keys there, the procedure applies less restrictive criteria to identify any keys that may be reasonably joined. It checks for keys with the same user datatypes, and if that fails, for columns with the same name and datatype. For complete information on the system procedures, see the Reference Manual.Determining which table columns to join 210 Adaptive Server EnterpriseTransact-SQL User’s Guide 211 C H A P T E R 7 Using and Creating Datatypes A datatype defines the kind of information each column in a table holds, and how that information is stored. You can use Adaptive Server system datatypes when you are defining columns, or you can create and use userdefined datatypes. This chapter discusses: How Transact-SQL datatypes work In Transact-SQL, datatypes specify the type of information, size, and storage format of table columns, stored procedure parameters, and local variables. For example, the int (integer) datatype stores whole numbers in the range of plus or minus 2 31 , and the tinyint (tiny integer) datatype stores whole numbers between 0 and 255 only. Adaptive Server supplies several system datatypes, and two user-defined datatypes, timestamp and sysname. You can use sp_addtype to build userdefined datatypes based on the system datatypes. You must specify a system datatype or user-defined datatype when declaring a column, local variable, or parameter. The following example uses the system datatypes char, numeric, and money to define the columns in the create table statement: create table sales_daily (stor_id char(4), ord_num numeric(10,0), Topic Page How Transact-SQL datatypes work 211 Using system-supplied datatypes 212 Converting between datatypes 223 Mixed-mode arithmetic and datatype hierarchy 224 Creating user-defined datatypes 226 Getting information about datatypes 229Using system-supplied datatypes 212 Adaptive Server Enterprise ord_amt money) The next example uses the bit system datatype to define the local variable in the declare statement: declare @switch bit Subsequent chapters describe in more detail how to declare columns, local variables, and parameters using the datatypes described in this chapter. You can determine which datatypes have been defined for columns of existing tables by using sp_help. Using system-supplied datatypes Table 7-1 lists the system-supplied datatypes provided for various types of information, the synonyms recognized by Adaptive Server, and the range and storage size for each. The system datatypes are printed in lowercase characters, although Adaptive Server allows you to enter them in either uppercase or lowercase. Most Adaptive Server-supplied datatypes are not reserved words and can be used to name other objects. Table 7-1: Adaptive Server system datatypes Datatypes by category Synonyms Range Bytes of storage Exact numeric: integers tinyint 0 to 255 (Negative numbers are not permitted.) 1 smallint 2 15 -1 (32,767) to -2 15 (-32,768) 2 int integer 2 31 -1 (2,147,483,647) to -2 31 (-2,147,483,648 4 Exact numeric: decimals numeric (p, s) 10 38 -1 to -10 38 2 to 17 decimal (p, s) dec 10 38 -1 to -10 38 2 to 17 Approximate numeric float (precision) machine dependent 4 for default precision < 16, 8 for default precision >= 16 double precision machine dependent 8 real machine dependent 4 Money smallmoney 214,748.3647 to -214,748.3648 4Chapter 7 Using and Creating Datatypes Transact-SQL User’s Guide 213 money 922,337,203,685,477.5807 to -922,337,203,685,477.5808 8 Date/time smalldatetime January 1, 1900 to June 6, 2079 4 datetime January 1, 1753 to December 31, 9999 8 date January 1, 0001 to December 31, 9999 4 time 12:00:00AM to 11:59:59:999PM 4 Character char(n) character pagesize n varchar(n) character varying, char varying pagesize actual entry length unichar Unicode character pagesize n * @@unicharsize (@@unicharsize equals 2) univarchar Unicode character varying, char varying pagesize actual number of characters * @@unicharsize nchar(n) national character, national char pagesize n * @@ncharsize nvarchar(n) nchar varying, national char varying, national character varying pagesize @@ncharsize * number of characters text 2 31 -1 (2,147,483,647) bytes or fewer 0 when uninitialized; multiple of 2K after initialization Binary binary(n) pagesize n varbinary(n) pagesize actual entry length image 2 31 -1 (2,147,483,647) bytes or fewer 0 when uninitialized; multiple of 2K after initialization Bit bit 0 or 1 1 (one byte holds up to 8 bit columns)) Datatypes by category Synonyms Range Bytes of storageUsing system-supplied datatypes 214 Adaptive Server Enterprise Exact numeric types: integers Adaptive Server provides three datatypes, tinyint, smallint, and int, to store integers (whole numbers). These types are exact numeric types; they preserve their accuracy during arithmetic operations. Choose among the integer types based on the expected size of the numbers to be stored. Internal storage size varies by datatype. Exact numeric types: decimal numbers Use the exact numeric types, numeric and decimal, for numbers that include decimal points. Data stored in numeric and decimal columns is packed to conserve disk space and preserves its accuracy to the least significant digit after arithmetic operations. The numeric and decimal types are identical in all respects but one: Only numeric types with a scale of 0 can be used for the IDENTITY column. The exact numeric types accept two optional parameters, precision and scale, enclosed within parentheses and separated by a comma: datatype [(precision [, scale ])] Adaptive Server defines each combination of precision and scale as a distinct datatype. For example, numeric(10,0) and numeric(5,0) are two separate datatypes. The precision and scale determine the range of values that can be stored in a decimal or numeric column: • The precision specifies the maximum number of decimal digits that can be stored in the column. It includes all digits to the right or left of the decimal point. You can specify a precision of 1–38 digits or use the default precision of 18 digits. • The scale specifies the maximum number of digits that can be stored to the right of the decimal point. The scale must be less than or equal to the precision. You can specify a scale of 0–38 digits or use the default scale of 0 digits. Exact numeric types with a scale of 0 display without a decimal point. You cannot enter a value that exceeds either the precision or the scale for the column. The storage size for a numeric or decimal column depends on its precision. The minimum storage requirement is 2 bytes for a 1- or 2-digit column. Storage size increases by 1 byte for each additional 2 digits of precision, to a maximum of 17 bytes.Chapter 7 Using and Creating Datatypes Transact-SQL User’s Guide 215 Approximate numeric datatypes The numeric types float, double precision, and real store numeric data that can tolerate rounding during arithmetic operations. Approximate numeric datatypes store, as binary tractions, slightly inaccurate representations of real numbers, stored as binary fractions. Anytime an approximate numeric value is displayed, printed, transferred between hosts, or used in calculations, the numbers lose precision. Note that isql displays only six significant digits after the decimal point and rounds the remainder. For more information on precision and approximate numeric datatypes, see the Reference Manual. Use the approximate numeric types for data that covers a wide range of values. They support all aggregate functions and all arithmetic operations except modulo (%). The real and double precision types are built on types supplied by the operating system. The float type accepts an optional precision in parentheses. float columns with a precision of 1–15 are stored as real; those with higher precision are stored as double precision. The range and storage precision for all three types is machine dependent. Money datatypes The money datatypes, money and smallmoney, store monetary data. You can use these datatypes for U.S. dollars and other decimal currencies, although Adaptive Server provides no means to convert from one currency to another. You can use all arithmetic operations except modulo, and all aggregate functions, with money and smallmoney data. Both money and smallmoney are accurate to one ten-thousandth of a monetary unit, but round values up to two decimal places for display purposes. The default print format places a comma after every three digits. Date and time datatypes Use the datetime and smalldatetime datatypes to store date and time information from January 1, 1753 through December 31, 9999. Use date for dates from January 1, 0001 to December 31, 9999 or time for 12:00:00 AM to 11:59:59:999. Dates outside this range must be entered, stored, and manipulated as char or varchar values.Using system-supplied datatypes 216 Adaptive Server Enterprise • datetime columns hold dates between January 1, 1753 and December 31, 9999. datetime values are accurate to 1/300 second on platforms that support this level of granularity. Storage size is 8 bytes: 4 bytes for the number of days since the base date of January 1, 1900 and 4 bytes for the time of day. • smalldatetime columns hold dates from January 1, 1900 to June 6, 2079, with accuracy to the minute. Its storage size is 4 bytes: 2 bytes for the number of days after January 1, 1900, and 2 bytes for the number of minutes after midnight. • date is a literal value consisting of a date portion in single or double quotes. This column can hold dates between January 1, 0001 to December 31, 9999. Storage size is 4 bytes. • time is a literal value consisting of a time portion enclosed in single or double quotes. This column holds time from 12:00:00AM to 11:59:59:999PM. Enclose date and time information in single or double quotes. You can enter it in either uppercase or lowercase letters and include spaces between data parts. Adaptive Server recognizes a wide variety of data entry formats, which are described in Chapter 9, “Adding, Changing, and Deleting Data.” However, Adaptive Server rejects values such as 0 or 00/00/00, which are not recognized as dates. The default display format for dates is “Apr 15 1987 10:23PM”. You can use the convert function for other styles of date display. You can also do some arithmetic calculations on datetime values with the built-in date functions, though Adaptive Server may round or truncate millisecond values, unless you use the time datatype. Character datatypes Use the character datatypes to store strings consisting of letters, numbers, and symbols entered within single or double quotes. You can use the like keyword to search these strings for particular characters and the built-in string functions to manipulate their contents. Strings consisting of numbers can be converted to exact and approximate numeric datatypes with the convert function, and then used for arithmetic.Chapter 7 Using and Creating Datatypes Transact-SQL User’s Guide 217 The char(n) datatype stores fixed-length strings, and the varchar(n) datatype stores variable-length strings, in single-byte character sets such as English. Their national character counterparts, nchar(n) and nvarchar(n), store fixed- and variable-length strings in multibyte character sets such as Japanese.The unichar and univarchar datatypes store Unicode characters, which are a constant size. You can specify the maximum number of characters with n or use the default column length of one character. For strings larger than the page size, use the text datatype. Table 7-2: Character datatypes Adaptive Server truncates entries to the specified column length without warning or error, unless you set string_rtruncation on. See the set command in the Reference Manual for more information. The empty string, ““or ‘’, is stored as a single space rather than as NULL. Thus, “abc” + ““ + “def” is equivalent to “abc def”, not to “abcdef”. Fixed- and variable-length columns behave somewhat differently: • Data in fixed-length columns is blank-padded to the column length. For the char and unichar datatypes, storage size is n bytes, (unichar = n*@@unicharsize); for the nchar datatype, n times the average national character length (@@ncharsize). When you create a char, unichar, or nchar column that allows nulls, Adaptive Server converts it to a varchar, univarchar, or nvarchar column and uses the storage rules for those datatypes. This is not true of char and nchar variables and parameters. • Data in variable-length columns is stripped of trailing blanks; storage size is the actual length of the data. For varchar or univarchar columns, this is the number of characters; for nvarchar columns, it is the number of characters times the average character length. Variable-length character data may require less space than fixed-length data, but it is accessed somewhat more slowly. Datatype Stores char(n) Fixed-length data, such as social security numbers or postal codes varchar(n) Data, such as names, that is likely to vary greatly in length unichar Fixed-length Unicode data, comparable to Char univarchar Unicode data that is likely to vary greatly in length, comparable to varchar nchar(n) Fixed-length data in multibyte character sets nvarchar(n) Variable-length data in multibyte character sets text Up to 2,147,483,647 bytes of printable characters on linked lists of data pages Using system-supplied datatypes 218 Adaptive Server Enterprise Unichar datatype The unichar and univarchar datatypes support the UTF-16 encoding of Unicode in the Adaptive Server. These datatypes are independent of the char and varchar datatypes, but mirror their behavior. For example, the built-in functions that operate on char and varchar also operate on unichar and univarchar. However, unichar and univarchar store only UTF-16 characters and have no connection to the default character set ID or the default sortorder ID as char and varchar do. To use the unichar and univarchar datatypes, the default character set for the server must be set to UTF-8. Each unichar/univarchar character requires two bytes of storage. The declaration of a unichar/univarchar column is the number of 16-bit Unicode values. The following example creates a table with one unichar column for 10 Unicode values requiring 20 bytes of storage: create table unitbl (unicol unichar(10)) The length of a unichar/univarchar column is limited by the size of a data page, just as the length of char/varchar columns. Note that Unicode surrogate pairs use the storage of two 16-bit Unicode values (i.e., four bytes). Be aware of this when declaring columns intended to store Unicode surrogate pairs. By default, Adaptive Server Enterprise correctly handles surrogates, taking care not to split the pair. Truncation of Unicode data is handled in a manner similar to that of char and varchar data. Unichar expressions can be used anywhere char expressions are used, including comparison operators, joins, subqueries, etc. Note however, that mixed-mode expressions of both unichar and char are performed as unichar. The number of Unicode values that can participate in such operations is limited to the maximum size of a unichar string. The normalization process modifies Unicode data so there is only a single representation in the database for a given sequence of abstract characters. Often, characters followed by combined diacritics are replaced by precombined forms. This allows significant performance optimizations. By default, the server assumes all Unicode data should be normalized.Chapter 7 Using and Creating Datatypes Transact-SQL User’s Guide 219 Relational expressions All relational expressions involving at least one expression of unichar or univarchar, will be based on the default Unicode sort order. If one expression is unichar and the other is varchar (nvarchar, char, or nchar), the latter will be implicitly converted to unichar. The following expressions are most often used in where clauses, where it may be combined with logical operators. When comparing Unicode character data “less than” means closer to the beginning of the default Unicode default sort order, and “greater than” means closer to the end. “Equality “means the Unicode default sort order makes no distinction between two values (although they need not be identical). For example, the precomposed character ê must be considered equal to the combining sequence consisting of the letter e followed by U+0302. If the Unicode normalization feature is turned on (the default), the Unicode data is automatically normalized and the server never sees unnormalized data. Table 7-3: Relational expressions Join operators Join operators appear in the same manner as comparison operators. In fact, any comparison operator can be used in a join. Expressions involving at least one expression of type unichar will be based on the default Unicode sort order. If one expression is of type unichar and the other type varchar (nvarchar, char, or nchar), the latter will be implicitly converted to unichar. expr1 op_compare [any | all] (subquery) The use of any or all with comparison operators and expr2 being a subquery, implicitly invokes min or max. For instance “expr1> any expr2” means, in effect, “expr1> min(expr2)”. expr1 [not] in (expression list) expr1 [not] in (subquery) The in operator checks for equality with each of the elements in expr2, which can be a list of constants, or the results of a subquery. expr1 [not] between expr2 and expr3 The between operator specifies a range. It is, in effect, shorthand for “expr1 = expr2 and expr1<= expr3”. expr1 [not] like “match_string” [escape “esc_char”] The like operator specifies a pattern to be matched. The semantics for pattern matching with Unicode data are the same for regular character data. If expr1 is a unichar column name, then “match_string” may be either a unichar string or a varchar string. In the latter case, an implicit conversion will take place between varchar and unicharUsing system-supplied datatypes 220 Adaptive Server Enterprise Union operators The union operator will operate with unichar data much like it does with varchar data. Corresponding columns from individual queries must be implicitly convertible to unichar, or explicit conversion must be used. Clauses and modifiers When unichar and univarchar columns are used in group by and order by clauses, equality is judged according to the default Unicode sort order. This is also true when using the distinct modifier. text datatype The text datatype stores up to 2,147,483,647 bytes of printable characters on linked lists of separate data pages. Each page stores a maximum of 1800 bytes of data. To save storage space, define text columns as NULL. When you initialize a text column with a non-null insert or update, Adaptive Server assigns a text pointer and allocates an entire 2K data page to hold the value. You cannot use the text datatype: • For parameters to stored procedures, as values passed to these parameters, or for local variables • For parameters to remote procedure calls (RPCs) • In order by, compute, group by, or union clauses • In an index • In subqueries or joins • In a where clause, except with the keyword like • With the + concatenation operator If you are using databases connected with Component Integration Services, there are several differences in the way text datatypes are handled. See the Component Integration Services User’s Guide for more information. For more information about the text datatype, see “Changing text and image data” on page 342.Chapter 7 Using and Creating Datatypes Transact-SQL User’s Guide 221 Binary datatypes The binary datatypes store raw binary data, such as pictures, in a hexadecimallike notation. Binary data begins with the characters “0x” and includes any combination of digits and the uppercase and lowercase letters A–F. The two digits following “0x” in binary and varbinary data indicate the type of number: “00” represents a positive number and “01” represents a negative number. If the input value does not include the “0x”, Adaptive Server assumes that the value is an ASCII value and converts it. Note Adaptive Server manipulates the binary types in a platform-specific manner. For true hexadecimal data, use the hextoint and inttohex functions. See Chapter 11, “Using the Built-In Functions in Queries.” Use the binary(n) and varbinary(n) datatypes to store data up to 255 bytes in length. Each byte of storage holds 2 binary digits. Specify the column length with n, or use the default length of 1 byte. If you enter a value longer than n, Adaptive Server truncates the entry to the specified length without warning or error. • Use the fixed-length binary type, binary(n), for data in which all entries are expected to have a similar length. Because entries in binary columns are zero-padded to the column length, they may require more storage space than those in varbinary columns, but they are accessed somewhat faster. • Use the variable-length binary type, varbinary(n), for data that is expected to vary greatly in length. Storage size is the actual size of the data values entered, not the column length. Trailing zeros are truncated. When you create a binary column that allows nulls, Adaptive Server converts it to a varbinary column and uses the storage rules for that datatype. You can search binary strings with the like keyword and operate on them with the built-in string functions. Because the exact form in which you enter a particular value depends upon the hardware you are using, calculations involving binary data may produce different results on different platforms. image datatype Use the image datatype to store larger blocks of binary data on external data pages. An image column can store up to 2,147,483,647 bytes of data on linked lists of data pages separate from other data storage for the table. Using system-supplied datatypes 222 Adaptive Server Enterprise When you initialize an image column with a non-null insert or update, Adaptive Server assigns a text pointer and allocates an entire 2K data page to hold the value. Each page stores a maximum of 1800 bytes. To save storage space, define image columns as NULL. To add image data without saving large blocks of binary data in your transaction log, use writetext. See the Reference Manual for details on writetext. You cannot use the image datatype: • For parameters to stored procedures, as values passed to these parameters, or for local variables • For parameters to remote procedure calls (RPCs) • In order by, compute, group by, or union clauses • In an index • In subqueries or joins • In a where clause, except with the keyword like • With the + concatenation operator • In the if update clause of a trigger If you are using databases connected with Component Integration Services, there are several differences in the way image datatypes are handled. See the Component Integration Services User’s Guide for more information. For more information about the image datatype, see “Changing text and image data” on page 342. The bit datatype Use bit columns for true and false or yes and no types of data. bit columns hold either 0 or 1. Integer values other than 0 or 1 are accepted, but are always interpreted as 1. Storage size is 1 byte. Multiple bit datatypes in a table are collected into bytes. For example, 7-bit columns fit into 1 byte; 9-bit columns take 2 bytes. Columns of datatype bit cannot be NULL and cannot have indexes on them. The status column in the syscolumns system table indicates the unique offset position for bit columns.Chapter 7 Using and Creating Datatypes Transact-SQL User’s Guide 223 The timestamp datatype The timestamp user-defined datatype is necessary for columns in tables that are to be browsed in Open Client™ DB-Library applications. Every time a row containing a timestamp column is inserted or updated, the timestamp column is automatically updated. A table can have only one column of the timestamp datatype. A column named timestamp automatically has the system datatype timestamp. Its definition is: varbinary(8) "NULL" Because timestamp is a user-defined datatype, you cannot use it to define other user-defined datatypes. You must enter it as “timestamp” in all lowercase letters. The sysname datatype sysname is a user-defined datatype that is used in the system tables. Its definition is: varchar(30) "NULL" You cannot use the sysname datatype to create a column. You can, however, create a user-defined datatype with a base type of sysname. You can then use this user-defined datatype to create columns. For more information about user-defined datatypes, see “Creating user-defined datatypes” on page 226. Converting between datatypes Adaptive Server automatically handles many conversions from one datatype to another. These are called implicit conversions. You can explicitly request other conversions with the convert, inttohex, and hextoint functions. Other conversions cannot be done, either explicitly or automatically, because of incompatibilities between the datatypes. For example, Adaptive Server automatically converts char expressions to datetime for the purposes of a comparison, if they can be interpreted as datetime values. However, for the purposes of display, you must use the convert function to convert char to int. Similarly, you must use convert on integer data if you want Adaptive Server to treat it as character data so that you can use the like keyword with it. Mixed-mode arithmetic and datatype hierarchy 224 Adaptive Server Enterprise The syntax for the convert function is: convert (datatype, expression, [style]) In the following example, convert displays the total_sales column using the char datatype, in order to display all sales beginning with the digit 2: select title, total_sales from titles where convert (char(20), total_sales) like "2%" The optional style parameter is used to convert datetime values to char or varchar datatypes to get a wide variety of date display formats. See Chapter 11, “Using the Built-In Functions in Queries” for details on the convert, inttohex, and hextoint functions. Mixed-mode arithmetic and datatype hierarchy When you perform arithmetic on values with different datatypes, Adaptive Server must determine the datatype and, in some cases, the length and precision, of the result. Each system datatype has a datatype hierarchy, which is stored in the systypes system table. User-defined datatypes inherit the hierarchy of the system type on which they are based. The following query ranks the datatypes in a database by hierarchy. In addition to the information shown below, your query results will include information about any user-defined datatypes in the database: select name, hierarchy from systypes order by hierarchy name hierarchy --------------------------- --------- floatn 1 float 2 datetimn 3 datetime 4 real 5 numericn 6 numeric 7 decimaln 8 decimal 9Chapter 7 Using and Creating Datatypes Transact-SQL User’s Guide 225 moneyn 10 money 11 smallmoney 12 smalldatetime 13 intn 14 int 15 smallint 16 tinyint 17 bit 18 univarchar 19 unichar 20 reserved 21 varchar 22 sysname 22 nvarchar 22 char 23 nchar 23 varbinary 24 timestamp 24 binary 25 text 26 image 27 (30 rows affected) The datatype hierarchy determines the results of computations using values of different datatypes. The result value is assigned the datatype that is closest to the top of the list. In the following example, qty from the sales table is multiplied by royalty from the roysched table. qty is a smallint, which has a hierarchy of 16; royalty is an int, which has a hierarchy of 15. Therefore, the datatype of the result is an int. smallint(qty) * int(royalty) = int Working with money datatypes If you are combining money and literals or variables, and you need results of money type, use money literals or variables: create table mytable (moneycol money,) insert into mytable values ($10.00) select moneycol * $2.5 from mytableCreating user-defined datatypes 226 Adaptive Server Enterprise If you are combining money with a float or numeric datatype from column values, use the convert function: select convert (money, moneycol * percentcol) from debits, interest drop table mytable Determining precision and scale For the numeric and decimal types, each combination of precision and scale is a distinct Adaptive Server datatype. If you perform arithmetic on two numeric or decimal values, n1 with precision p1 and scale s1, and n2 with precision p2 and scale s2, Adaptive Server determines the precision and scale of the results as shown in Table 7-4: Table 7-4: Precision and scale after arithmetic operations Creating user-defined datatypes A Transact-SQL enhancement to SQL allows you to name and design your own datatypes to supplement the system datatypes. A user-defined datatype is defined in terms of system datatypes. You can give one name to a frequently used datatype definition. This makes it easy for you to custom fit datatypes to columns. Note To use a user-defined datatype in more than one database, create it in the model database. The user-defined datatype definition then becomes known to all new databases you create. Once you define a datatype, it can be used as the datatype for any column in the database. For example, tid is used as the datatype for columns in several pubs2 tables: titles.title_id, titleauthor.title_id, sales.title_id, and roysched.title_id. Operation Precision Scale n1 + n2 max(s1, s2) + max(p1 -s1, p2 - s2) + 1 max(s1, s2) n1 - n2 max(s1, s2) + max(p1 -s1, p2 - s2) + 1 max(s1, s2) n1 * n2 s1 + s2 + (p1 - s1) + (p2 - s2) + 1 s1 + s2 n1 / n2 max(s1 + p2 + 1, 6) + p1 - s1 + p2 max(s1 + p2 -s2 + 1, 6)Chapter 7 Using and Creating Datatypes Transact-SQL User’s Guide 227 The advantage of user-defined datatypes is that you can bind rules and defaults to them for use in several tables. For more about this topic, see Chapter 13, “Defining Defaults and Rules for Data.” Use sp_addtype to create user datatypes. It takes as parameters the name of the user datatype being created, the Adaptive Server-supplied datatype from which it is being built, and an optional NULL, NOT NULL, or IDENTITY specification. You can build a user-defined datatype using any system datatype other than timestamp. User-defined datatypes have the same datatype hierarchy as the system datatypes on which they are based. Unlike Adaptive Server-supplied datatypes, user-defined datatype names are case-sensitive. Here is the syntax for sp_addtype: sp_addtype datatypename, phystype [ (length) | (precision [, scale] ) ] [, "identity" |nulltype] Here is how tid was defined: sp_addtype tid, "char(6)", "not null" You must enclose a parameter within single or double quotes if it includes a blank or some form of punctuation, or if it is a keyword other than null (for example, identity or sp_helpgroup). In this example, quotes are required around char(6) because of the parentheses, but around “not null” because of the blank. They are not required around tid. Specifying length, precision, and scale When you build a user-defined datatype based upon certain Adaptive Server datatypes, you must specify additional parameters: • The char, nchar, varchar, nvarchar, binary, and varbinary datatypes expect a length in parentheses. If you do not supply one, Adaptive Server assumes the default length of 1 character. • The float datatype expects a precision in parentheses. If you do not supply one, Adaptive Server uses the default precision for your platform. • The numeric and decimal datatypes expect a precision and scale, in parentheses and separated by a comma. If you do not supply them, Adaptive Server uses a default precision of 18 and scale of 0.Creating user-defined datatypes 228 Adaptive Server Enterprise You cannot change the length, precision, or scale specification when you include the user-defined datatype in a create table statement. Specifying null type The null type determines how the user-defined datatype treats nulls. You can create a user-defined datatype with a null type of “null”, “NULL”, “nonull”, “NONULL”, “not null”, or “NOT NULL”. bit and IDENTITY types do not allow null values. If you omit the null type, Adaptive Server uses the null mode defined for the database (by default, NOT NULL). For compatibility with the SQL standards, use sp_dboption to set the allow nulls by default option to true. You can override the null type when you include the user-defined datatype in a create table statement. Associating rules and defaults with user-defined datatypes Once you have created a user-defined datatype, use sp_bindrule and sp_bindefault to associate rules and defaults with the datatype. Use sp_help to print a report that lists the rules, defaults, and other information associated with the datatype. Rules and defaults are discussed in Chapter 13, “Defining Defaults and Rules for Data.” For complete information on, and syntax for, system procedures, see the Reference Manual. Creating a user-defined datatype with the IDENTITY property To create a user-defined datatype with the IDENTITY property, use sp_addtype. The new type must be based on a physical type of numeric with a scale of 0: sp_addtype typename, "numeric (precision, 0)", "identity" The following example creates a user-defined type, IdentType, with the IDENTITY property: sp_addtype IdentType, "numeric(4,0)", "identity"Chapter 7 Using and Creating Datatypes Transact-SQL User’s Guide 229 When you create a column from an IDENTITY type, you can specify either identity or not null—or neither one—in the create or alter table statement. The column automatically inherits the IDENTITY property. Here are three different ways to create an IDENTITY column from the IdentType user-defined type: create table new_table (id_col IdentType) drop table new_table create table new_table (id_col IdentType identity) drop table new_table create table new_table (id_col IdentType not null) drop table new_table Note If you try to create a column that allows nulls from an IDENTITY type, the create table or alter table statement fails. Creating IDENTITY columns from other user-defined datatypes You can create IDENTITY columns from user-defined datatypes that do not have the IDENTITY property. The user-defined types must have a physical datatype of numeric with a scale of 0 and must be defined as not null. Dropping a user-defined datatype To drop a user-defined datatype, execute sp_droptype: sp_droptype typename Note You cannot drop a datatype that is already in use in any table. Getting information about datatypes Use sp_help to display information about the properties of a system datatype or a user-defined datatype. The report indicates the base type from which the datatype was created, whether it allows nulls, the names of any rules and defaults bound to the datatype, and whether it has the IDENTITY property.Getting information about datatypes 230 Adaptive Server Enterprise The following examples display the information about the money system datatype and the tid user-defined datatype: sp_help money Type_name Storage_type Length Prec Scale ---------- ------------ ------ ----- ----- money money 8 NULL NULL Nulls Default_name Rule_name Identity ----- ------------ --------- -------- 1 NULL NULL NULL (return status = 0) sp_help tid Type_name Storage_type Length Prec Scale ---------- ------------ ------ ----- ----- tid varchar 6 NULL NULL Nulls Default_name Rule_name Identity ----- ------------ --------- -------- 0 NULL NULL 0 (return status = 0)Transact-SQL User’s Guide 231 C H A P T E R 8 Creating Databases and Tables This chapter describes how to create databases and tables. This chapter includes these sections: For information on managing databases, see the System Administration Guide. What are databases and tables? A database stores information (data) in a set of database objects, such as tables, that relate to each other. A table is a collection of rows that have associated columns containing individual data items. You define how your data is organized when you create your databases and tables. This process is called data definition. Adaptive Server database objects include: • Tables Topic Page What are databases and tables? 231 Using and creating databases 234 Altering the sizes of databases 239 Dropping databases 240 Creating tables 240 Managing identity gaps in tables 254 Defining integrity constraints for tables 263 How to design and create a table 274 Creating new tables from query results: select into 277 Altering existing tables 283 Dropping tables 302 Assigning permissions to users 303 Getting information about databases and tables 305What are databases and tables? 232 Adaptive Server Enterprise • Rules • Defaults • Stored procedures • Triggers • Views • Referential integrity constraints • Check integrity constraints This chapter covers the creation, modification, and deletion of databases and tables, including integrity constraints. Columns and datatypes define the type of data included in tables and are discussed in this chapter. Indexes describe how data is organized in tables. They are not considered database objects by Adaptive Server and are not listed in sysobjects. Indexes are discussed in Chapter 12, “Creating Indexes on Tables.” Enforcing data integrity in databases Data integrity refers to the correctness and completeness of data within a database. To enforce data integrity, you can constrain or restrict the data values that users can insert, delete, or update in the database. For example, the integrity of data in the pubs2 and pubs3 databases requires that a book title in the titles table must have a publisher in the publishers table. You cannot insert books that do not have a valid publisher into titles, because it violates the data integrity of pubs2 or pubs3. Transact-SQL provides several mechanisms for integrity enforcement in a database such as rules, defaults, indexes, and triggers. These mechanisms allow you to maintain these types of data integrity: • Requirement – requires that a table column must contain a valid value in every row; it cannot allow null values. The create table statement allows you to restrict null values for a column. • Check or Validity – limits or restricts the data values inserted into a table column. You can use triggers or rules to enforce this type of integrity. • Uniqueness – no two table rows can have the same non-null values for one or more table columns. You can use indexes to enforce this integrity.CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 233 • Referential – data inserted into a table column must already have matching data in another table column or another column in the same table. A single table can have up to 192 references. Consistency of data values in the database is another example of data integrity, which is described in Chapter 19, “Transactions: Maintaining Data Consistency and Recovery.” As an alternative to using rules, defaults, indexes, and triggers, Transact-SQL provides a series of integrity constraints as part of the create table statement to enforce data integrity as defined by the SQL standards. These integrity constraints are described later in this chapter. Permissions within databases Whether or not you can create and drop databases and database objects depends on your permissions or privileges. Ordinarily, a System Administrator or Database Owner sets up the permissions for you, based on the kind of work you do and the functions you need. These permissions can be different for each user in a given installation or database. You can determine what your permissions are by executing: sp_helprotect user_name user_name is your Adaptive Server login name. To make your experiments with database objects as convenient as possible, the pubs2 and pubs3 databases have a “guest” user name in their sysusers system tables. The scripts that create pubs2 and pubs3 grant a variety of permissions to “guest”. The “guest” mechanism means that anyone who has a login on Adaptive Server, that is, anyone who is listed in master..syslogins, has access to pubs2 and pub3, and permission to create and drop such objects as tables, indexes, defaults, rules, procedures, and so on. The “guest” user name also allows you to use certain stored procedures, create user-defined datatypes, query the database, and modify the data in it. Using and creating databases 234 Adaptive Server Enterprise To use the pubs2 or pubs3 database, issue the use command. Adaptive Server checks whether you are listed under your own name in pubs2.sysusers or pubs3..sysusers. If not, you are admitted as a guest without any action on your part. If you are listed in the sysusers table for pubs2 or pubs3, Adaptive Server admits you as yourself, but may give you different permissions from those of “guest.” Note All the examples in this chapter assume you are being treated as “guest.” Most users can look at the system tables in the master database by means of the “guest” mechanism previously described. Users who are not recognized by name in the master database are allowed in and treated as a user named “guest.” The “guest” user is added to the master database in the script that creates the master database when it is installed. A Database Owner, “dbo”, can add a “guest” user to any user database using sp_adduser. System Administrators automatically become the Database Owner in any database they use. For more information, see the System Administration Guide and the Reference Manual. Using and creating databases A database is a collection of related tables and other database objects—views, indexes, and so on. When you install Adaptive Server, it contains these system databases: • The master database controls the user databases and the operation of Adaptive Server as a whole. • The sybsystemprocs database contains the system stored procedures. • The sybsystemdb database contains information about distributed transactions. • The temporary database, tempdb, stores temporary objects, including temporary tables created with the name prefix “tempdb..”. • The model database is used by Adaptive Server as a template for creating new user databases. In addition, System Administrators can install these optional databases:CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 235 • pubs2 – a sample database that contains data representing a publishing operation. You can use this database to test your server connections and learn Transact-SQL. Most of the examples in the Adaptive Server documentation query the pubs2 database. • pubs3 – a version of pubs2 that uses referential integrity examples. pubs3 has a table, store_employees, that uses a self-referencing column. pubs3 also includes an IDENTITY column in the sales table. Additionally, the primary keys in its master tables use nonclustered unique indexes, and the titles table has an example of the numeric datatype. • interpubs – similar to pubs2, but contains French and German data. • jpubs – similar to pubs2, but contains Japanese data. Use it if you have installed the Japanese Language Module. These optional databases are user databases. All of your data is stored in user databases. Adaptive Server manages each database by means of system tables. The data dictionary tables in the master database and in other databases are considered system tables. Choosing a database: use The use command lets you access an existing database. Its syntax is: use database_name For example, to access the pubs2 database, type: use pubs2 This command allows you to access the pubs2 database only if you are a known user in pubs2. Otherwise, you see an error message. It is likely that you will be automatically connected to the master database when you log in to Adaptive Server, so if you want to use another database, issue the use command. You or a System Administrator can change the database to which you initially connect by using sp_modifylogin. Only a System Administrator can change the default database for another user. Using and creating databases 236 Adaptive Server Enterprise Creating a user database: create database You can create a new database if a System Administrator has granted you permission to use create database. You must be using the master database when you create a new database. In many enterprises, a System Administrator creates all databases. The creator of a database is its owner. Another user who creates a database for you can transfer ownership of it using sp_changedbowner. The Database Owner is responsible for giving users access to the database and for granting and revoking certain other permissions to users. In some organizations, the Database Owner is also responsible for maintaining regular backups of the database and for reloading it in case of system failure. The Database Owner can temporarily attain any other user’s permissions on a database by using the setuser command. Because each database is allocated a significant amount of space, even if it contains only small amounts of data, you may not have permission to use create database. The simplest form of create database is: create database database_name To create a new database called newpubs database, first verify you are using the master database rather than pubs2, and then type this command: use master create database newpubs drop database newpubs use pubs2 A database name must be unique on Adaptive Server, and must follow the rules for identifiers described under “Identifiers” on page 7. Adaptive Server can manage up to 32,767 databases. You can create only one database at a time. The maximum number of segments for any database is 32. Adaptive Server creates a new database as a copy of the model database, which contains the system tables that belong in every user database. The creation of a new database is recorded in the master database tables sysdatabases and sysusages. The full syntax of create database is: create database database_name [on {default | database_device} [= size] [, database_device [= size]]...] [log on database_device [= size] [, database_device [= size]]...]CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 237 [with override] [for load] This chapter describes all the create database options except with override. For information about with override, see the System Administration Guide. The on clause The optional on clause allows you to specify where to store the database and how much space in megabytes to allocate for it. If you use the keyword default, the database is assigned to an available database device in the pool of default database devices indicated in the master database table sysdevices. Use sp_helpdevice to see which devices are in the default list. Note A System Administrator may have made certain storage allocations based on performance statistics and other considerations. Before creating databases, you should check with a System Administrator. To specify a size of 5MB for a database to be stored in this default location, use on default = size: use master create database newpubs on default = 5 drop database newpubs use pubs2 To specify a different location for the database, give the logical name of the database device where you want it stored. A database can be stored on more than one database device, with different amounts of space on each. This example creates the newpubs database and allocates 3MB to it on pubsdata and 2MB on newdata: create database newpubs on pubsdata = 3, newdata = 2 If you omit the on clause and the size, the database is created with 2MB of space from the pool of default database devices indicated in sysdevices. A database allocation can range in size from 2MB to 2 23 MB.Using and creating databases 238 Adaptive Server Enterprise The log on clause Unless you are creating very small, noncritical databases, always use the log on database_device extension to create database. This places the transaction logs on a separate database device. There are several reasons for placing the logs on a separate device: • It allows you to use dump transaction rather than dump database, thus saving time and tapes. • It allows you to establish a fixed size for the log, keeping it from competing with other database activity for space. Additional reasons for placing the log on a separate physical device from the data tables are: • It improves performance. • It ensures full recovery in the event of hard disk failures. The following command places the log for newpubs on the logical device pubslog, with a size of 1MB: create database newpubs on pubsdata = 3, newdata = 2 log on pubslog = 1 Note When you use the log on extension, you are placing the database transaction log on a segment named “logsegment”. To add more space for an existing log, use alter database and, in some cases, sp_extendsegment. See the Reference Manual or the System Administration Guide for details. The size of the device required for the transaction log varies according to the amount of update activity and the frequency of transaction log dumps. As a rule of thumb, allocate to the log between 10 and 25 percent of the space you allocate to the database. The for load option The optional for load clause invokes a streamlined version of create database that you can use only for loading a database dump. Use the for load option for recovery from media failure or for moving a database from one machine to another. See the System Administration Guide for more information.CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 239 Altering the sizes of databases If a database has filled its allocated storage space, you cannot add new data or updates to it. Existing data, of course, is always preserved. If the space allocated for a database proves to be too small, the Database Owner can increase it with the alter database command. alter database permission defaults to the Database Owner, and cannot be transferred. You must be using the master database to use alter database. The default increase is 2MB from the default pool of space. This statement adds 2MB to newpubs on the default database device: alter database newpubs The full alter database syntax allows you to extend a database by a specified number of megabytes (minimum 1MB) and to specify where the storage space is to be added: alter database database_name [on {default | database_device} [= size] [, database_device [= size]]...] [log on {default | database_device} [ = size ] [, database_device [= size]]...] [with override] [for load] The on clause in the alter database command is just like the on clause in create database. The for load clause is just like the for load clause in create database and can be used only on a database created with the for load clause. To increase the space allocated for newpubs by 2MB on the database device pubsdata, and by 3MB on the database device newdata, type: alter database newpubs on pubsdata = 2, newdata = 3 When you use alter database to allocate more space on a device already in use by the database, all of the segments already on that device use the added space fragment. All the objects already mapped to the existing segments can now grow into the added space. The maximum number of segments for any database is 32. Dropping databases 240 Adaptive Server Enterprise When you use alter database to allocate space on a device that is not yet in use by a database, the system and default segments are mapped to the new device. To change this segment mapping, use sp_dropsegment to drop the unwanted segments from the device. Note Using sp_extendsegment automatically unmaps the system and default segments. For information about with override, see the System Administration Guide. Dropping databases Use the drop database command to remove a database. drop database deletes the database and all of its contents from Adaptive Server, frees the storage space that had been allocated for it, and deletes references to it from the master database. The syntax is: drop database database_name [, database_name]... You cannot drop a database that is in use, that is, open for reading or writing by any user. As indicated, you can drop more than one database in a single command. For example: drop database newpubs, newdb You cannot remove damaged database with drop database. Use dbcc dbrepair instead. Creating tables When you create a table, you name its columns and supply a datatype for each column. You can also specify whether a particular column can hold null values or specify integrity constraints for columns in the table. There can be as many as 2,000,000,000 tables per database.CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 241 Maximum number of columns per table The maximum number of columns in a table depends on many factors, including, among others, your server’s logical page size and whether the tables are configured for allpages- or data only-locking. For a complete description of the maximum number of columns per table, see the create table command in the Reference Manual. Example of creating a table Use the newpubs database you created in the previous section if you want to try these examples. Otherwise, these changes will affect another database, like pubs2 or pubs3. The simplest form of |create|table| is: create table table_name (column_name datatype) For example, to create a table named names with one column named some_name, and a fixed length of 11 bytes, enter: create table names (some_name char(11)) drop table names If you have set quoted_identifier on, both the table name and the column names can be delimited identifiers. Otherwise, they must follow the rules for identifiers described under “Identifiers” on page 7. Column names must be unique within a table, but you can use the same column name in different tables in the same database. There must be a datatype for each column. The word “char” after the column name in the example above refers to the datatype of the column—the type of value that column will contain. Datatypes are discussed in Chapter 7, “Using and Creating Datatypes.” The number in parentheses after the datatype gives the maximum number of bytes that can be stored in the column. You give a maximum length for some datatypes. Others have a system-defined length.Creating tables 242 Adaptive Server Enterprise Be sure to put parentheses around the list of column names, and commas after each column definition. The last column definition does not need a comma after it. Note A variable cannot be used in a default if the default is part of a create table statement. Choosing table names The create table command builds the new table in the currently open database. Table names must be unique for each user. You can create temporary tables either by preceding the table name in a create table statement with a pound sign (#) or by specifying the name prefix “tempdb..”. For more information, see “Using temporary tables” on page 250. You can use any tables or other objects that you have created without qualifying their names. You can also use objects created by the Database Owner without qualifying their names, as long as you have the appropriate permissions on them. These rules hold for all users, including the System Administrator and the Database Owner. Different users can create tables of the same name. For example, a user named “jonah” and a user named “sally” can each create a table named info. Users who have permissions on both tables have to qualify them as jonah.info and sally.info. Sally must qualify references to Jonah’s table as jonah.info, but she can refer to her own table simply as info. create table syntax The syntax of create table is: create table [database.[owner].]table_name (column_name datatype [default {constant_expression | user | null}] {[{identity | null | not null}] [off row | in row] [[constraint constraint_name] {{unique | primary key} [clustered | nonclustered] [asc | desc] [with {fillfactor = pct, max_rows_per_page = num_rows, reservepagegap = num_pages}]CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 243 [on segment_name] | references [[database.]owner.]ref_table [ ref_column)] | check (search_condition)}]}... | [constraint constraint_name] {{unique | primary key} [clustered | nonclustered] (column_name [asc | desc] [{, column_name [asc | desc]}...]) [with {fillfactor = pct max_rows_per_page = num_rows , reservepagegap = num_pages }] [on segment_name] |foreign key (column_name [{,column_name}...]) references [[database.]owner.]ref_table [(ref_column [{, ref_column}...])] | check (search_condition) ...} [{, {next_column | next_constraint}}...]) [lock {datarows | datapages | allpages}] [with {max_rows_per_page = num_rows, exp_row_size = num_bytes, reservepagegap = num_pages, identity_gap = num_values}] [on segment_name ] [[external table] at pathname] Note For a complete discussion of the syntax, see create table in the Reference Manual. The create table statement: • Defines each column in the table. • Provides the column name and datatype and specifies how each column handles null values. • Specifies which column, if any, has the IDENTITY property. • Defines column-level integrity constraints and table-level integrity constraints. Each table definition can have multiple constraints per column and per table. For example, the create table statement for the titles table in the pubs2 database is: create table titles (title_id tid, title varchar(80) not null, type char(12), Creating tables 244 Adaptive Server Enterprise pub_id char(4) null, price money null, advance money null, royalty int null, total_sales int null, notes varchar(200) null, pubdate datetime, contract bit not null) The following sections describe components of table definition: systemsupplied datatypes, user-defined datatypes, null types, and IDENTITY columns. Note The on segment_name extension to create table allows you to place your table on an existing segment. segment_name points to a specific database device or a collection of database devices. Before creating a table on a segment, see a System Administrator or the Database Owner for a list of segments that you can use. Certain segments may be allocated to specific tables or indexes for performance reasons, or for other considerations. Allowing null values For each column, you can specify whether to allow null values. A null value is not the same as “zero” or “blank.” NULL means no entry has been made, and usually implies “value unknown” or “value not applicable.” It indicates that the user did not make any entry, for whatever reason. For example, a null entry in the price column of the titles table does not mean that the book is being given away free, but that the price is not known or has not yet been set. If the user does not make an entry in a column defined with the keyword null, Adaptive Server supplies the value “NULL”. A column defined with the keyword null also accepts an explicit entry of NULL from the user, no matter what datatype it is. Be careful when you enter null values in character columns. If you put the word “null” inside single or double quotes, Adaptive Server interprets the entry as a character string rather than as the value NULL. If you omit null or not null in the create table statement, Adaptive Server uses the null mode defined for the database (by default, NOT NULL). Use sp_dboption to set the allow nulls by default option to true. You must make an entry in a column defined as NOT NULL; otherwise, Adaptive Server displays an error message. CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 245 Defining columns as NULL provides a placeholder for data you may not yet know. For example, in the titles table, price, advance, royalty, and total_sales are set up to allow NULL. However, title_id and title are not, because the lack of an entry in these columns would be meaningless and confusing. A price without a title makes no sense, whereas a title without a price simply means that the price has not been set yet or is not available. In create table , use the keywords not null when the information in the column is critical to the meaning of the other columns. Constraints and rules used with null values You cannot define a column to allow null values, and then override this definition with a constraint or a rule that prohibits null values. For example, if a column definition specifies NULL and a rule specifies: @val in (1,2,3) An implicit or explicit NULL does not violate the rule. The column definition overrides the rule, even a rule that specifies: @val is not null See “Defining integrity constraints for tables” on page 263 for more information on constraints. Rules are covered in detail in Chapter 13, “Defining Defaults and Rules for Data.” Defaults and null values You can use defaults, that is, values that are supplied automatically when no entry is made, with both NULL and NOT NULL columns. A default counts as an entry. However, you cannot designate a NULL default for a NOT NULL column. You can specify null values as defaults using the default constraint of create table or using create default. The default constraint is described later in this chapter; create default is described in Chapter 13, “Defining Defaults and Rules for Data.” If you specify NOT NULL when you create a column and do not create a default for it, an error message occurs when a user fails to make an entry in that column during an insert. In addition, the user cannot insert or update such a column with NULL as a value. Creating tables 246 Adaptive Server Enterprise Table 8-1illustrates the interaction between a column’s default and its null type when a user specifies no column value or explicitly enters a NULL value. The three possible results are a null value for the column, the default value for the column, or an error message. Table 8-1: Column definition and null defaults Nulls require variable length datatypes Only columns with variable-length datatypes can store null values. When you create a NULL column with a fixed-length datatype, Adaptive Server converts it to the corresponding variable-length datatype. Adaptive Server does not inform you of the type change. Table 8-2 lists the fixed-length datatypes and the variable-length datatypes to which Adaptive Server converts them. Certain variable-length datatypes, such as moneyn, are reserved; you cannot use them to create columns, variables, or parameters. Column definition User entry Result Null and default defined Enters no value Enters NULL value Default used NULL used Null defined, no default defined Enters no value Enters NULL value NULL used NULL used Not null, default defined Enters no value Enters NULL value Default used NULL used Not null, no default defined Enters no value Enters NULL value Error ErrorCHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 247 Table 8-2: Conversion of fixed-length to variable-length datatypes Data entered into char, nchar, and binary columns follows the rules for variablelength columns, rather than being padded with spaces or zeros to the full length of the column specification. text and image columns text and image columns created with insert and NULL are not initialized and contain no value. They do not use storage space and cannot be accessed with readtext or writetext. When a NULL value is written in a text or image column with update, the column is initialized, a valid text pointer to the column is inserted into the table, and a 2K data page is allocated to the column. Once the column is initialized, it can be accessed by readtext and writetext. See the Adaptive Server for more information. Using IDENTITY columns An IDENTITY column contains a value for each row, generated automatically by Adaptive Server, that uniquely identifies the row within the table. Each table can have only one IDENTITY column. You can define an IDENTITY column when you create a table with a create table or select into statement, or add it later with an alter table statement. IDENTITY columns cannot be updated and do not allow nulls. Original Fixed-Length Datatype Converted To char varchar nchar nvarchar binary datetime datetimn float floatn int, smallint, and tinyint intn decimal decimaln numeric numericn money and smallmoney moneynCreating tables 248 Adaptive Server Enterprise You define an IDENTITY column by specifying the keyword identity, instead of null or not null, in the create table statement. IDENTITY columns must have a datatype of numeric and scale of 0. Define the IDENTITY column with any desired precision, from 1 to 38 digits, in a new table: create table table_name (column_name numeric(precision ,0) identity) The maximum possible column value is 10 precision - 1. For example, this command creates a table with an IDENTITY column that allows a maximum value of 10 5 - 1, or 9999: create table sales_daily (sale_id numeric(5,0) identity, stor_id char(4) not null) You can create automatic IDENTITY columns by using the auto identity database option and the size of auto identity configuration parameter. To include IDENTITY columns in nonunique indexes, use the identity in nonunique index database option. Note By default, Adaptive Server begins numbering rows with the value 1, and continues numbering rows consecutively as they are added. Some activities, such as manual insertions, deletions, or transaction rollbacks, and server shutdowns or failures, can create gaps in IDENTITY column values. Adaptive Server provides several methods of controlling identity gaps described in “Managing identity gaps in tables” on page 254. Creating IDENTITY columns with user-defined datatypes You can use user-defined datatypes to create IDENTITY columns. The userdefined datatype must have an underlying type of numeric and a scale of 0. If the user-defined datatype was created with the IDENTITY property, you do not have to repeat the identity keyword when creating the column. This example shows a user-defined datatype with the IDENTITY property: sp_addtype ident, "numeric(5)", "identity" This example shows an IDENTITY column based on the ident datatype: create table sales_monthly (sale_id ident, stor_id char(4) not null)CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 249 If the user-defined type was created as not null, you must specify the identity keyword in the create table statement. You cannot create an IDENTITY column from a user-defined datatype that allows null values. Referencing IDENTITY columns When you create a table column that references an IDENTITY column, as with any referenced column, make sure it has the same datatype definition as the IDENTITY column. For example, in the pubs3 database, the sales table is defined using the ord_num column as an IDENTITY column: create table sales (stor_id char(4) not null references stores(stor_id), ord_num numeric(6,0) identity, date datetime not null, unique nonclustered (ord_num)) Notice that the ord_num IDENTITY column is defined as a unique constraint, which it needs for referencing the ord_num column in salesdetail. salesdetail is defined as follows: create table salesdetail (stor_id char(4) not null references storesz(stor_id), ord_num numeric(6,0) references salesz(ord_num), title_id tid not null references titles(title_id), qty smallint not null, discount float not null) An easy way to insert a row into salesdetail after inserting a row into sales is to use the @@identity global variable to insert the IDENTITY column value into salesdetail. The @@identity global variable stores the most recently generated IDENTITY column value. For example: begin tran insert sales values ("6380", "04/25/97") insert salesdetail values ("6380", @@identity, "TC3218", 50, 50) commit tran This example is in a transaction because both inserts depend on each other to succeed. For example, if the sales insert fails, the value of @@identity will be different, resulting in an erroneous row being inserted into salesdetail. Because the two inserts are in a transaction, if one fails, the entire transaction is rejected.Creating tables 250 Adaptive Server Enterprise For more information on IDENTITY columns, see “Retrieving IDENTITY column values with @@identity” on page 331. For information on transactions, see Chapter 19, “Transactions: Maintaining Data Consistency and Recovery.” Referring to IDENTITY columns with syb_identity Once you have defined an IDENTITY column, you do not have to remember the actual column name. You can use the syb_identity keyword, qualified by the table name where necessary, in a select, insert, update, or delete statement on the table. For example, this query selects the row for which sale_id equals 1: select * from sales_monthly where syb_identity = 1 Creating “hidden” IDENTITY columns automatically System Administrators can use the auto identity database option to automatically include a 10-digit IDENTITY column in new tables. To turn this feature on in a database, use: sp_dboption database_name, "auto identity", "true" Each time a user creates a new table without specifying either a primary key, a unique constraint, or an IDENTITY column, Adaptive Server automatically defines an IDENTITY column. The IDENTITY column is not visible when you use select * to retrieve all columns from the table. You must explicitly include the column name, SYB_IDENTITY_COL (all uppercase letters), in the select list. If Component Integration Services is enabled, the automatic IDENTITY column for proxy tables is called OMNI_IDENTITY_COL. To set the precision of the automatic IDENTITY column, use the size of auto identity configuration parameter. For example, to set the precision of the IDENTITY column to 15 use: sp_configure "size of auto identity", 15 Using temporary tables Temporary tables are created in the tempdb database. To create a temporary table, you must have create table permission in tempdb. create table permission defaults to the Database Owner.CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 251 To make a table temporary, use the pound sign (#) or “tempdb..” before the table name in the create table statement. There are two kinds of temporary tables: • Tables that can be shared among Adaptive Server sessions You create a shareable temporary table by specifying tempdb as part of the table name in the create table statement. For example, the following statement creates a temporary table that can be shared among Adaptive Server sessions: create table tempdb..authors (au_id char(11)) drop table tempdb..authors Adaptive Server does not change the names of temporary tables created this way. The table exists until the current session ends or until its owner drops it using drop table. • Tables that are accessible only by the current Adaptive Server session or procedure You create a nonshareable temporary table by specifying a pound sign (#) before the table name in the create table statement. For example: create table #authors (au_id char (11)) The table exists until the current session or procedure ends, or until its owner drops it using drop table. If you do not use the pound sign or “tempdb..” before the table name, and you are not currently using tempdb, the table is created as a permanent table. A permanent table stays in the database until it is explicitly dropped by its owner. This statement creates a nonshareable temporary table: create table #myjobs (task char(30), start datetime, stop datetime, notes varchar(200)) You can use this table to keep a list of today’s chores and errands, along with a record of when you start and finish, and any comments you may have. This table and its data will automatically be deleted at the end of the current work session. Temporary tables are not recoverable.Creating tables 252 Adaptive Server Enterprise You can associate rules, defaults, and indexes with temporary tables, but you cannot create views on temporary tables or associate triggers with them. You can use a user-defined datatype when creating a temporary table only if the datatype exists in tempdb..systypes. To add an object to tempdb for the current session only, execute sp_addtype while using tempdb. To add an object permanently, execute sp_addtype in model, then restart Adaptive Server so model is copied to tempdb. Ensuring that the temporary table name is unique To ensure that a temporary table name is unique for the current session, Adaptive Server: • Truncates the table name to 13 characters, including the pound sign (#) • Pads shorter names to 13 characters, using underscores (_) • Appends a 17-digit numeric suffix that is unique for an Adaptive Server session The following example shows a table created as #temptable and stored as #temptable___00000050010721973: use pubs2 go create table #temptable (task char(30)) go use tempdb go select name from sysobjects where name like "#temptable%" go name ------------------------------ #temptable___00000050010721973 (1 row affected) Manipulating temporary tables in stored procedures Stored procedures can reference temporary tables that are created during the current session. Within a stored procedure, you cannot create a temporary table, drop it, and then create a new temporary table with the same name. CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 253 Temporary tables with names beginning with “#” Temporary tables with names beginning with “#” that are created within stored procedures disappear when the procedure exits. A single procedure can: • Create a temporary table • Insert data into the table • Run queries on the table • Call other procedures that reference the table Since the temporary table must exist in order to create procedures that reference it, here are the steps to follow: 1 Use create table to create the temporary table. 2 Create the procedures that access the temporary table, but do not create the procedure that creates the table. 3 Drop the temporary table. 4 Create the procedure that creates the table and calls the procedures created in step 2. tables with names beginning with tempdb.. You can create temporary tables without the # prefix, using create table tempdb..tablename from inside a stored procedure. These tables do not disappear when the procedure completes, so they can be referenced by independent procedures. Follow the steps above to create these tables. Warning! Create temporary tables with the “tempdb..” prefix from inside a stored procedure only if you intend to share the table among users and sessions. Stored procedures that create and drop a temporary table should use the # prefix to avoid inadvertent sharing. General rules on temporary tables Temporary tables with names that begin with # are subject to the following restrictions: • You cannot create views on these tables. • You cannot associate triggers with these tables. • You cannot tell which session or procedure has created these tables.Managing identity gaps in tables 254 Adaptive Server Enterprise These restrictions do not apply to shareable, temporary tables created in tempdb. Rules that apply to both types of temporary tables: • You can associate rules, defaults, and indexes with temporary tables. Indexes created on a temporary table disappear when the temporary table disappears. • System procedures such as sp_help work on temporary tables only if you invoke them from tempdb. • You cannot use user-defined datatypes in temporary tables unless the datatypes exist in tempdb; that is, unless the datatypes have been explicitly created in tempdb since the last time Adaptive Server was restarted. • You do not have to set the select into/bulkcopy option on to select into a temporary table. Creating tables in different databases As the create table syntax shows, you can create a table in a database other than the current one by qualifying the table name with the name of the other database. However, you must be an authorized user of the database in which you are creating the table, and you must have create table permission in it. If you are using pubs2 or pubs3 and there is another database called newpubs, you can create a table called newtab in newpubs like this: create table newpubs..newtab (col1 int) You cannot create other database objects—views, rules, defaults, stored procedures, and triggers—in a database other than the current one. Managing identity gaps in tables The IDENTITY column contains a unique ID number, generated by Adaptive Server, for each row in a table. Because of the way the server generates ID numbers by default, you may occasionally have large gaps in the ID numbers. The identity_gap parameter gives you control over ID numbers, and potential gaps in them, for a specific table.CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 255 By default, Adaptive Server allocates a block of ID numbers in memory instead of writing each ID number to disk as it is needed, which requires more processing time. The server writes the highest number of each block to the table’s object allocation map (OAM) page. This number is used as the starting point for the next block after the currently allocated block of numbers is used or “burned”. The other numbers of the block are held in memory, but are not saved to disk. Numbers are considered burned when they are allocated to memory, then deleted from memory either because they were assigned to a row, or because they were erased from memory due to some abnormal occurrence such as a system failure. Allocating a block of ID numbers improves performance by reducing contention for the table. However, if the server fails or is shut down with no wait before all the ID numbers are assigned, the unused numbers are burned. When the server is running again, it starts numbering with the next block of numbers based on the highest number of the previous block that the server wrote to disk. Depending on how many allocated numbers were assigned to rows before the failure, you may have a large gap in the ID numbers. Identity gaps can also result from dumping and loading an active database. When dumping, database objects are saved to the OAM page. If an object is currently being used, the ‘maximum used identity value’ is not be in the OAM page and, therefore, is not dumped. Parameters for controlling identity gaps Adaptive Server provides parameters that allow you to control gaps in identity numbers as described in Table 8-3. Table 8-3: Parameters for controlling identity gaps Parameter Name Scope Used with Description identity_gap table-specific create table or select into Creates ID number blocks of a specific size for a specific table. Overrides identity burning set factor for the table. Works with identity grab size.Managing identity gaps in tables 256 Adaptive Server Enterprise Comparison of identity burning set factor and identity_gap The identity_gap parameter gives you control over the size of identity gaps for a particular table as illustrated in the following examples. In the examples, we have created a table named books to list all the books in our bookstore. We want each book to have a unique ID number, and we want Adaptive Server to automatically generate the ID numbers. Example of using identity burning set factor When defining the IDENTITY column for the books table, we used the default numeric value of (18, 0), which provides a total of 999,999,999,999,999,999 ID numbers. For the identity burning set factor configuration parameter, we are using the default setting of 5000 (.05 percent of 999,999,999,999,999,999), which means that Adaptive Server allocates blocks of 500,000,000,000,000 numbers. identity burning set factor server-wide sp_configure Indicates a percentage of the total available ID numbers you want to have allocated for each block. Works with identity grab size. If the identity_gap for a table is set to 1 or higher, identity burning set factor has no effect on that table. The burning set factor is used for all tables for which identity_gap is set to 0. When you set identity burning set factor, you express the number in decimal form, and then multiply it by 10,000,000 (10 7 ) to get the correct value to use with sp_configure. For example, to release 15 percent (.15) of the potential IDENTITY column values at one time, you specify a value of .15 times 10 7 (or 1,500,000): sp_configure "identity burning set factor", 1500000 identity grab size server-wide sp_configure Reserves a block of contiguous ID numbers for each process. Works with identity burning set factor and identity_gap. Parameter Name Scope Used with DescriptionCHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 257 The server allocates the first 500,000,000,000,000 numbers in memory and stores the highest number of the block (500,000,000,000,000) on the table’s OAM page. When all the numbers are assigned to rows or burned, the server takes the next block of numbers (the next 500,000,000,000,000), starting with 500,000,000,000,001, and stores the number 1,000,000,000,000,000 as the highest number of the block. Let’s say, after row number 500,000,000,000,022 the server fails. Only numbers 1 through 500,000,000,000,022 were used as ID numbers for books. Numbers 500,000,000,000,023 through 1,000,000,000,000,000 are burned. When the server is running again, it creates ID numbers starting from the highest number stored on the table’s OAM page plus one (1,000,000,000,000,001),which leaves a gap of 499,999,999,999,978 ID numbers. To reduce this large gap in identity numbers for a specific table, you can set the identity gap as described in “Example of using identity_gap.” Example of using identity_gap In this case, we create the books table with an identity_gap value of 1000. This overrides the server-wide identity burning set factor setting that resulted in blocks of 500,000,000,000,000 ID numbers. Instead, ID numbers are allocated in memory in blocks of 1000. The server allocates the first 1000 numbers and stores the highest number of the block (1000) to disk. When all the numbers are used, the server takes the next 1000 numbers, starting with 1001, and stores the number 2000 as the highest number. Now, let’s say that after row number 1002 we lose power, which causes the server to fail. Only the numbers 1000 through 1002 were used, and numbers 1003 through 2000 are lost. When the server is running again, it creates ID numbers starting from the highest number stored on the table’s OAM page plus one (2000), which leaves a gap of only 998 numbers. You can significantly reduce the gap in ID numbers by setting the identity_gap for a table instead of using the server-wide table burning set factor. However, there may be a performance cost to setting this value too low. Each time the server must write the highest number of a block to disk, performance is affected. For example, if identity_gap is set to 1, which means you are allocating one ID number at a time, the server must write the new number every time a row is created, which may reduce performance because of page lock contention on the table. You must find the best setting to achieve the optimal performance with the lowest gap value acceptable for your situation.Managing identity gaps in tables 258 Adaptive Server Enterprise Setting the table-specific identity gap Set the table-specific identity gap when you create a table using either create table or select into. Setting identity gap with create table The syntax is: create table table_name (column_name datatype(constant_expression) identity) with identity_gap = value For example: create table mytable (IdNum numeric(12,0) identity) with identity_gap = 10 This statement creates a table named mytable with an identity column. The identity gap is set to 10, which means ID numbers will be allocated in memory in blocks of ten. If the server fails or is shut down with no wait, the maximum gap between the last ID number assigned to a row and the next ID number assigned to a row is ten numbers. Setting identity gap with select into If you are creating a table in a select into statement from a table that has a specific identity gap setting, the new table does not inherit the identity gap setting from the parent table. Instead, the new table uses the identity burning set factor setting. To give the new table a specific identity_gap setting, specify the identity gap in the select into statement. You can give the new table an identity gap that is the same as or different from the parent table. For example, to create a new table (newtable) from the existing table (mytable) with an identity gap: select identity into newtable with identity_gap = 20 from mytable Changing the table-specific identity gap To change the identity gap for a specific table, use sp_chgattribute: sp_chgattribute "table_name", "identity_gap", set_numberCHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 259 where: • table_name is the name of the table for which you want to change the identity gap. • identity_gap indicates that you want to change the identity gap. • set_number is the new size of the identity gap. For example: sp_chgattribute "mytable", "identity_gap", 20 To change mytable to use the identity burning set factor setting instead of the identity_gap setting, set identity_gap to 0: sp_chgattribute "mytable", "identity_gap", 0 Displaying table-specific identity gap information To see the identity_gap setting for a table, use sp_help. For example, the zero value in the identity_gap column (towards the end of the output) indicates that no table-specific identity gap is set. mytable uses the server-wide identity burning set factor value. sp_help mytable Name Owner Type ------------------------------ ----------------------- ------- ---------------------- mytable dbo user table (1 row affected) Data_located_on_segment When_created ------------------------------ ----------------------- --- default Jun 8 1999 5:35PM Column_name Type Length Prec Scale Nulls Default_name Rule_name Identity --------------- --------------- ------ ---- ----- ---- - --------------- --------------- --------Managing identity gaps in tables 260 Adaptive Server Enterprise idnum numeric 6 12 0 0 NULL NULL 1 Object does not have any indexes. No defined keys for this object. Object is not partitioned. Lock scheme Allpages The attribute ’exp_row_size’ is not applicable to tables with allpages lock scheme. The attribute ’concurrency_opt_threshold’ is not applicable to tables with allpages lock scheme. exp_row_size reservepagegap fillfactor max_rows_per_page identity_gap ------------ -------------- ---------- -------------- --- ------------ 1 0 0 0 0 concurrency_opt_threshold ------------------------- 0 If you change the identity_gap of mytable to 20, the sp_help output for the table shows 20 in the identity_gap column. This setting overrides the server-wide identity burning set factor value. sp_help mytable Name Owner Type ------------------------------ ----------------------- ------- ---------------------- mytable dbo user table (1 row affected) Data_located_on_segment When_created ------------------------------ ----------------------- --- default Jun 8 1999 5:35PM Column_name Type Length Prec Scale Nulls Default_name Rule_name Identity --------------- --------------- ------ ---- ----- ---- - --------------- CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 261 --------------- -------- idnum numeric 6 12 0 0 NULL NULL 1 Object does not have any indexes. No defined keys for this object. Object is not partitioned. Lock scheme Allpages The attribute ’exp_row_size’ is not applicable to tables with allpages lock scheme. The attribute ’concurrency_opt_threshold’ is not applicable to tables with allpages lock scheme. exp_row_size reservepagegap fillfactor max_rows_per_page identity_gap ------------ -------------- ---------- --------------- -- ------------ 1 0 0 0 2 0 concurrency_opt_threshold ------------------------- 0 Gaps due to insertions, deletions, identity grab size, and rollbacks Manual insertions into the IDENTITY column, deletion of rows, the value of the identity grab size configuration parameter, and transaction rollbacks can create gaps in IDENTITY column values. These gaps are not affected by the setting of the identity burning set factor configuration parameter. For example, assume that you have an IDENTITY column with these values: select syb_identity from stores_cal id_col ------- 1 2 3 4 5 (5 rows affected) You can delete all rows for which the IDENTITY column falls between 2 and 4, leaving gaps in the column values:Managing identity gaps in tables 262 Adaptive Server Enterprise delete stores_cal where syb_identity between 2 and 4 select syb_identity from stores_cal id_col ------ 1 5 (2 rows affected) After setting identity_insert on for the table, the table owner, Database Owner, or System Administrator can manually insert any legal value greater than 5. For example, inserting a value of 55 would create a large gap in IDENTITY column values: insert stores_cal (syb_identity, stor_id, stor_name) values (55, "5025", "Good Reads") select syb_identity from stores_cal id_col ------- 1 5 55 (3 rows affected) If identity_insert is then set to off, Adaptive Server assigns an IDENTITY column value of 55 + 1, or 56, for the next insertion. If the transaction that contains the insert statement is rolled back, Adaptive Server discards the value 56 and uses a value of 57 for the next insertion. If table inserts reach the IDENTITY column’s maximum value The maximum number of rows you can insert into a table depends on the precision set for the IDENTITY column. If a table reaches that limit, you can either re-create the table with a larger precision or, if the table’s IDENTITY column is not used for referential integrity, use the bcp utility to remove the gaps. See “Reaching the IDENTITY column’s maximum value” on page 333 for more information.CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 263 Defining integrity constraints for tables Transact-SQL provides two methods for maintaining data integrity in a database: • Defining rules, defaults, indexes, and triggers • Defining create table integrity constraints Choosing one method over the other depends on your requirements. Integrity constraints offer the advantages of defining integrity controls in one step during the table creation process (as defined by the SQL standards) and of simplifying the process to create those integrity controls. However, integrity constraints are more limited in scope and less comprehensive than defaults, rules, indexes, and triggers. For example, triggers provide more complex handling of referential integrity than those declared in create table. Also, the integrity constraints defined by a create table are specific for that table; you cannot bind them to other tables, and you can only drop or change them using alter table. Constraints cannot contain subqueries or aggregate functions, even on the same table. The two methods are not mutually exclusive. You can use integrity constraints along with defaults, rules, indexes, and triggers. This gives you the flexibility to choose the best method for your application. This section describes the create table integrity constraints. Defaults, rules, indexes, and triggers are described in later chapters. You can create the following types of constraints: • unique and primary key constraints require that no two rows in a table have the same values in the specified columns. In addition, a primary key constraint requires that there not be a null value in any row of the column. • Referential integrity (references) constraints require that data being inserted in specific columns already have matching data in the specified table and columns. Use sp_helpconstraint to find a table’s referenced tables. • check constraints limit the values of data inserted into columns. You can also enforce data integrity by restricting the use of null values in a column (the null or not null keywords) and by providing default values for columns (the default clause). See “Allowing null values” on page 244 for information about the null and not null keywords.Defining integrity constraints for tables 264 Adaptive Server Enterprise For information about any constraints defined for a table, see “Using sp_helpconstraint to find a table’s constraint information” on page 307. Warning! Do not define or alter the definitions of constraints for system tables. Specifying table-level or column-level constraints You can declare integrity constraints at the table or column level. Although the difference is rarely noticed by users, column-level constraints are only checked if a value in the column is being modified, while the table-level constraints are checked if there is any modification to a row, regardless of whether or not it changes the column in question. You place column-level constraints after the column name and datatype, but before the delimiting comma. You enter table-level constraints as separate comma-delimited clauses. Adaptive Server treats table-level and column-level constraints the same way; both ways are equally efficient However, you must declare constraints that operate on more than one column as table-level constraints. For example, the following create table statement has a check constraint that operates on two columns, pub_id and pub_name: create table my_publishers (pub_id char(4), pub_name varchar(40), constraint my_chk_constraint check (pub_id in ("1389", "0736", "0877") or pub_name not like "Bad News Books")) You can declare constraints that operate on just one column as column-level constraints, but it is not required. For example, if the above check constraint uses only one column (pub_id), you can place the constraint on that column: create table my_publishers (pub_id char(4) constraint my_chk_constraint check (pub_id in ("1389", "0736", "0877")), pub_name varchar(40))CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 265 In either case, the constraint keyword and accompanying constraint_name are optional. The check constraint is described under “Specifying check constraints” on page 271. Note You cannot issue create table with a check constraint and then insert data into the table in the same batch or procedure. Either separate the create and insert statements into two different batches or procedures, or use execute to perform the actions separately. Creating error messages for constraints You can create error messages and bind them to constraints by creating messages with sp_addmessage and binding them to constraints with sp_bindmsg. For example: sp_addmessage 25001, "The publisher ID must be 1389, 0736, or 0877" sp_bindmsg my_chk_constraint, 25001 insert my_publishers values ("0000", "Reject This Publisher") Msg 25001, Level 16, State 1: Server ‘snipe’, Line 1: The publisher ID must be 1389, 0736, or 0877 Command has been aborted. To change the message for a constraint, bind a new message. The new message replaces the old message. Unbind messages from constraints using sp_unbindmsg; drop user-defined messages using sp_dropmessage. For example: sp_unbindmsg my_chk_constraint sp_dropmessage 25001 To change the text of a message but keep the same error number, unbind it, drop it with sp_dropmessage, add it again with sp_addmessage, and bind it with sp_bindmsg. Defining integrity constraints for tables 266 Adaptive Server Enterprise After creating a check constraint After you create a check constraint, the source text describing the check constraint is stored in the text column of the syscomments system table. Do not remove this information from syscomments; doing so can cause problems for future upgrades of Adaptive Server. If you have security concerns, encrypt the text in syscomments by using sp_hidetext, described in the Reference Manual. For more information, see “Compiled objects” on page 4. Specifying default column values Before you define any column-level integrity constraints, you can specify a default value for the column with the default clause. The default clause assigns a default value to a column as part of the create table statement. When a user does not enter a value for the column, Adaptive Server inserts the default value. You can use the following values with the default clause: • constant_expression – specifies a constant expression to use as a default value for the column. It cannot include the name of any columns or other database objects, but you can include built-in functions that do not reference database objects. This default value must be compatible with the datatype of the column. • user – specifies that Adaptive Server insert the user name as the default. The datatype of the column must be either char(30) or varchar(30) to use this default. • null – specifies that Adaptive Server insert the null value as the default. You cannot define this default for columns that do not allow null values (using the notnull keyword). For example, this create table statement defines two column defaults: create table my_titles (title_id char(6), title varchar(80), price money default null, total_sales int default 0) You can include only one default clause per column in a table. Using the default clause to assign defaults is simpler than the two-step Transact-SQL method. In Transact-SQL, you can use create default to declare the default value and then bind it to the column with sp_bindefault.CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 267 Specifying unique and primary key constraints You can declare unique or primary key constraints to ensure that no two rows in a table have the same values in the specified columns. Both constraints create unique indexes to enforce this data integrity. However, primary key constraints are more restrictive than unique constraints. Columns with primary key constraints cannot contain a NULL value. You normally use a table’s primary key constraint in conjunction with referential integrity constraints defined on other tables. The definition of unique constraints in the SQL standards specifies that the column definition shall not allow null values. By default, Adaptive Server defines the column as not allowing null values (if you have not changed this using sp_dboption) when you omit null or not null keywords in the column definition. In Transact-SQL, you can define the column to allow null values along with the unique constraint, since the unique index used to enforce the constraint allows you to insert a null value. Note Do not confuse the unique and primary key integrity constraints with the information defined by sp_primarykey, sp_foreignkey, and sp_commonkey. The unique and primary key constraints actually create indexes to define unique or primary key attributes of table columns. sp_primarykey, sp_foreignkey, and sp_commonkey define the logical relationship of keys (in the syskeys table) for table columns, which you enforce by creating indexes and triggers. unique constraints create unique nonclustered indexes by default; primary key constraints create unique clustered indexes by default. You can declare either clustered or nonclustered indexes with either type of constraint. For example, the following create table statement uses a table-level unique constraint to ensure that no two rows have the same values in the stor_id and ord_num columns: create table my_sales (stor_id char(4), ord_num varchar(20), date datetime, unique clustered (stor_id, ord_num)) There can be only one clustered index on a table, so you can specify only one unique clustered or primary key clustered constraint. Defining integrity constraints for tables 268 Adaptive Server Enterprise You can use the unique and primary key constraints to create unique indexes (including the with fillfactor, with max_rows_per_page, and on segment_name options) when enforcing data integrity. However, indexes provide additional capabilities. For information about indexes and their options, including the differences between clustered and nonclustered indexes, see Chapter 12, “Creating Indexes on Tables.” Specifying referential integrity constraints Referential integrity refers to the methods used to manage the relationships between tables. When you create a table, you can define constraints to ensure that the data inserted into a particular column has matching values in another table. There are three types of references you can define in a table: references to another table, references from another table, and self-references, that is, references within the same table. The following two tables from the pubs3 database illustrate how declarative referential integrity works. The first table, stores, is a “referenced” table: create table stores (stor_id char(4) not null, stor_name varchar(40) null, stor_address varchar(40) null, city varchar(20) null, state char(2) null, country varchar(12) null, postalcode char(10) null, payterms varchar(12) null, unique nonclustered (stor_id)) The second table, store_employees, is a “referencing table” because it contains a reference to the stores table. It also contains a self-reference: create table store_employees (stor_id char(4) null references stores(stor_id), emp_id id not null, mgr_id id null references store_employees(emp_id), emp_lname varchar(40) not null, emp_fname varchar(20) not null, phone char(12) null, address varchar(40) null,CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 269 city varchar(20) null, state char(2) null, country varchar(12) null, postalcode varchar(10) null, unique nonclustered (emp_id)) The references defined in the store_employees table enforce the following restrictions: • Any store specified in the store_employees table must be included in the stores table. The references constraint enforces this by saying that any value inserted into the stor_id column in store_employees must already exist in the stor_id column in my_stores. • All managers must have employee identification numbers. The references constraint enforces this by saying that any value inserted into the mgr_id column must already exist in the emp_id column. Table-level or column-level referential integrity constraints You can define referential integrity constraints at the column level or the table level. The referential integrity constraints in the preceding examples were defined at the column level, using the references keyword in the create table statement. When you define table-level referential integrity constraints, include the foreign key clause and a list of one or more column names. foreign key specifies that the listed columns in the current table are foreign keys whose target keys are the columns listed the following references clause. For example: constraint sales_detail_constr foreign key (stor_id, ord_num) references my_salesdetail(stor_id, ord_num) The foreign key syntax is permitted only for table-level constraints, and not for column-level constraints. For more information, see “Specifying table-level or column-level constraints” on page 264. After defining referential integrity constraints at the column level or the table level, you can use sp_primarykey, sp_foreignkey, and sp_commonkey to define the keys in the syskeys system table.Defining integrity constraints for tables 270 Adaptive Server Enterprise Maximum number of references allowed for a table The maximum number of references allowed for a table is 192. You can check a table’s references by using sp_helpconstraint, described under “Using sp_helpconstraint to find a table’s constraint information” on page 307. Using create schema for cross-referencing constraints You cannot create a table that references a table that does not yet exist. To create two or more tables that reference each other, use create schema. A schema is a collection of objects owned by a particular user, and the permissions associated with those objects. If any of the statements within a create schema statement fail, the entire command is rolled back as a unit, and none of the commands take effect. The create schema syntax is: create schema authorization authorization name create_object_statement [create_object_statement ...] [permission_statement ...] For example: create schema authorization dbo create table list1 (col_a char(10) primary key, col_b char(10) null references list2(col_A)) create table list2 (col_A char(10) primary key, col_B char(10) null references list1(col_a)) General rules for creating referential integrity constraints When you define referential integrity constraints in a table: • Make sure you have references permission on the referenced table. For information about permissions, see the System Administration Guide. • Make sure that the referenced columns are constrained by a unique index in the referenced table. You can create that unique index using either the unique or primary key constraint or the create index statement. For example, the referenced column in the stores table is defined as: stor_id char(4) primary keyCHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 271 • Make sure the columns used in the references definition have matching datatypes. For example, the stor_id columns in both my_stores and store_employees were created using the char(4) datatype. The mgr_id and emp_id columns in store_employees were created with the id datatype. • You can omit column names in the references clause only if the columns in the referenced table are designated as a primary key through a primary key constraint. • You cannot delete rows or update column values from a referenced table that match values in a referencing table. Delete or update from the referencing table first, and then delete it from the referenced table. Similarly, you cannot use truncate table on a referenced table. Truncate the referencing table first, and then truncate the referenced table. • You must drop the referencing table before you drop the referenced table; otherwise, a constraint violation occurs. • Use sp_helpconstraint to find a table’s referenced tables. Referential integrity constraints provide a simpler way to enforce data integrity than triggers. However, triggers provide additional capabilities to enforce referential integrity between tables. For more information, see Chapter 17, “Triggers: Enforcing Referential Integrity.” Specifying check constraints You can declare a check constraint to limit the values users insert into a column in a table. Check constraints are useful for applications that check a limited, specific range of values. A check constraint specifies a search_condition that any value must pass before it is inserted into the table. A search_condition can include: • A list of constant expressions introduced with in • A range of constant expressions introduced with between • A set of conditions introduced with like, which may contain wildcard characters An expression can include arithmetic operations and Transact-SQL built-in functions. The search_condition cannot contain subqueries, a set function specification, or a target specification. For example, this statement ensures that only certain values can be entered for the pub_id column:Defining integrity constraints for tables 272 Adaptive Server Enterprise create table my_new_publishers (pub_id char(4) check (pub_id in ("1389", "0736", "0877", "1622", "1756") or pub_id like "99[0-9][0-9]"), pub_name varchar(40), city varchar(20), state char(2)) Column-level check constraints can reference only the column on which the constraint is defined; they cannot reference other columns in the table. Tablelevel check constraints can reference any columns in the table. create table allows multiple check constraints in a column definition. Because check constraints do not override column definitions, you cannot use a check constraint to prohibit null values if the column definition permits them. If you declare a check constraint on a column that allows null values, you can insert NULL into the column, implicitly or explicitly, even though NULL is not included in the search_condition. For example, suppose you define the following check constraint on a table column that allows null values: check (pub_id in ("1389", "0736", "0877", "1622", "1756")) You can still insert NULL into that column. The column definition overrides the check constraint because the following expression always evaluates to true: col_name != null Designing applications that use referential integrity When you design applications that use referential integrity features: • Do not create unnecessary referential constraints. The more referential constraints a table has, the slower a statement requiring referential integrity runs on that table. • Use as few self-referencing constraints on a table as possible. • Use the check constraint rather than the references constraint for applications that check a limited, specific range of values. Using the check constraint eliminates the need for Adaptive Server to scan other tables to complete the query, since there are no references. Therefore, queries on such tables run faster than on tables using references. For example, this table uses a check constraint to limit the authors to California:CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 273 create table cal_authors (au_id id not null, au_lname varchar(40) not null, au_fname varchar(20) not null, phone char(12) null, address varchar(40) null, city varchar(20) null, state char(2) null check(state = "CA"), country varchar(12) null, postalcode char(10) null) • Bind commonly scanned foreign key indexes to their own caches, to optimize performance. Unique indexes are created automatically on columns declared as primary keys. These indexes are usually selected to scan the referenced table when their corresponding foreign keys are updated or inserted. • Keep multi-row updates of candidate keys at a minimum. • Put referential integrity queries into procedures that use constraint checks. Constraint checks are compiled into the execution plan; when a referential constraint is altered, the procedure that has the constraint compiled is automatically recompiled when that procedure is executed. • If you cannot embed referential integrity queries in a procedure and you frequently have to run referential integrity queries in an ad hoc batch, bind the system catalog sysreferences to its own cache. This improves performance when Adaptive Server needs to recompile referential integrity queries. • After you create a table that has referential constraints, test it by using set showplan, noexec on before running a query using the table. The showplan output indicates the number of auxiliary scan descriptors required to run the query; scan descriptors manage the scan of a table whenever queries are run on it. If the number of auxiliary scan descriptors is very high, either redesign the table so it uses fewer scan descriptors, or increase the value of the number of auxiliary scan descriptors configuration parameter.How to design and create a table 274 Adaptive Server Enterprise How to design and create a table This section gives an example of a create table statement you can use to create a practice table of your own. If you do not have create table permission, see a System Administrator or the owner of the database in which you are working. Creating a table usually implies creating indexes, defaults, and rules to go with it. Custom datatypes, triggers, and views are frequently involved, too. Of course, you can create a table, input some data, and work with it for a while before you create indexes, defaults, rules, triggers, or views. This allows you to see what kind of transactions are most common and what kind of data is frequently entered. On the other hand, it is often most efficient to design a table and all the components that go with it at once. Here is an outline of the steps you go through. You might find it easiest to sketch your plans on paper before you actually create a table and its accompanying objects. First, plan the table’s design: 1 Decide what columns you need in the table, and the datatype, length, precision, and scale, for each. 2 Create any new user-defined datatypes before you define the table where they are to be used. 3 Decide which column, if any, should be the IDENTITY column. 4 Decide which columns should and which should not accept null values. 5 Decide what integrity constraints or column defaults, if any, you need to add to the columns in the table. This includes deciding when to use column constraints and defaults instead of defaults, rules, indexes, and triggers to enforce data integrity. 6 Decide whether you need defaults and rules, and if so, where and what kind. Consider the relationship between the NULL and NOT NULL status of a column and defaults and rules. 7 Decide what kind of indexes you need and where. Indexes are discussed in Chapter 12, “Creating Indexes on Tables.” Now, create the table and its associated objects: 1 Create the table and its indexes using create table and create index. 2 Create the defaults and rules you need with the create default and create rule. These commands are discussed in Chapter 13, “Defining Defaults and Rules for Data.”CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 275 3 Bind any defaults and rules you need with sp_bindefault and sp_bindrule. If there were any defaults or rules on a user-defined datatype that you used in a create table statement, they are automatically in force. These system procedures are discussed in Chapter 15, “Using Stored Procedures.” 4 Create triggers using create trigger. Triggers are discussed in Chapter 17, “Triggers: Enforcing Referential Integrity.” 5 Create views using create view. Views are discussed in Chapter 10, “Views: Limiting Access to Data.” Make a design sketch The table called friends_etc is used in this chapter and subsequent chapters to illustrate how to create indexes, defaults, rules, triggers, and so forth. It can hold names, addresses, telephone numbers, and personal information about your friends. It does not define any column defaults or integrity constraints, so as to not conflict with those objects. If another user has already created the friends_etc table, check with a System Administrator or the Database Owner if you plan to follow the examples and create the objects that go with friends_etc. The owner of friends_etc will need to drop its indexes, defaults, rules, and triggers so that there will be no conflict when you create these objects. Table 8-4 shows the proposed structure of the friends_etc table and the indexes, defaults, and rules that go with each column. Table 8-4: Sample table design Column Datatype Null? Index Default Rule pname nm NOT NULL nmind(composite) sname nm NOT NULL nmind(composite) address varchar(30) NULL city varchar(30) NOT NULL citydflt state char(2) NOT NULL statedflt zip char(5) NULL zipind zipdflt ziprule phone p# NULL phonerule age tinyint NULL agerule bday datetime NOT NULL bdflt gender bit NOT NULL gndrdflt debt money NOT NULL gndrdflt notes varchar(255) NULLHow to design and create a table 276 Adaptive Server Enterprise Create the user-defined datatypes The first two columns are for the personal (first) name and surname. They are defined as nm datatype. Before you create the table, you need to create the datatype. The same is true of the p# datatype for the phone column: execute sp_addtype nm, "varchar(30)" execute sp_addtype p#, "char(10)" The nm datatype allows for a variable-length character entry with a maximum of 30 bytes. The p# datatype allows for a char datatype with a fixed-length size of 10 bytes. Choose the columns that accept null values Except for columns that are assigned user-defined datatypes, each column has an explicit NULL or NOT NULL entry. You do not need to specify NOT NULL in the table definition, because it is the default. This table design specifies NOT NULL explicitly, for readability. The NOT NULL default means that an entry is required for that column, for example, for the two name columns in this table. The other data is meaningless without the names. In addition, the gender column must be NOT NULL because you cannot use NULL with bit columns. If a column is designated NULL and a default is bound to it, the default value, rather than NULL, is entered when no other value is given on input. If a column is designated NULL and a rule is bound to it that does not specify NULL, the column definition overrides the rule when no value is entered for the column. Columns can have both defaults and rules. The relationship between these two is discussed in Chapter 13, “Defining Defaults and Rules for Data.” Define the table Now, write the create table statement: create table friends_etc (pname nm not null, sname nm not null, address varchar(30) null, city varchar(30) not null, state char(2) not null, postalcode char(5) null, phone p# null, CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 277 age tinyint null, bday datetime not null, gender bit not null, debt money not null, notes varchar(255) null) You have now defined columns for the personal name and surname, address, city, state, postal code, telephone number, age, birthday, gender, debt information, and notes. Later, you will create the rules, defaults, indexes, triggers, and views for this table. Creating new tables from query results: select into The select into command lets you create a new table based on the columns specified in the select statement’s select list and the rows chosen in the where clause. The into clause is useful for creating test tables, new tables as copies of existing tables, and for making several smaller tables out of one large table. You can use select into on a permanent table only if the select into/bulkcopy/pllsort database option is set to on. A System Administrator can turn on this option using sp_dboption. Use sp_helpdb to see if this option is on. Here is what sp_helpdb and its results look like when the select into/bulkcopy/pllsort database option is set to on: sp_helpdb pubs2 name db_size owner dbid created status --------- ------- ------ ----- ----------- ------ ------ pubs 2 MB sa 5 Jun 5 1997 select into /bulkcopy/pllsort (1 row affected) device size usage ----------------- --------- -------------- master 2 MB data and log (1 row affected) sp_helpdb output indicates whether the option is set to on or off. Only the System Administrator or the Database Owner can set the database options.Creating new tables from query results: select into 278 Adaptive Server Enterprise If the select into/bulkcopy/pllsort database option is on, you can use the select into clause to build a new permanent table without using a create table statement. You can select into a temporary table, even if the select into/bulkcopy/pllsort option is not on. Note Because select into is a minimally logged operation, use dump database to back up your database following a select into. You cannot dump the transaction log following a minimally logged operation. Unlike a view that displays a portion of a table, a table created with select into is a separate, independent entity. See Chapter 10, “Views: Limiting Access to Data,” for more information. The new table is based on the columns you specify in the select list, the tables you name in the from clause, and the rows you choose in the where clause. The name of the new table must be unique in the database and must conform to the rules for identifiers. A select statement with an into clause allows you to define a table and put data into it, based on existing definitions and data, without going through the usual data definition process. The following example shows a select into statement and its results. A table called newtable is created, using two of the columns in the four-column table publishers. Because this statement includes no where clause, data from all the rows (but only the two specified columns) of publishers is copied into newtable. select pub_id, pub_name into newtable from publishers (3 rows affected) “3 rows affected” refers to the three rows inserted into newtable. Here’s what newtable looks like: select * from newtable pub_id pub_name ------ ------------------------------------ 0736 New Age Books 0877 Binnet & Hardley 1389 Algodata Infosystems (3 rows affected) The new table contains the results of the select statement. It becomes part of the database, just like its parent table. CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 279 You can create a skeleton table with no data by putting a false condition in the where clause. For example: select * into newtable2 from publishers where 1=2 (0 rows affected) select * from newtable2 pub_id pub_name city state ------ -------------- -------- ----- (0 rows affected) No rows are inserted into the new table, because 1 never equals 2. You can also use select into with aggregate functions to create tables with summary data: select type, "Total_amount" = sum(advance) into #whatspent from titles group by type (6 rows affected) select * from #whatspent type Total_amount ------------ ------------------------ UNDECIDED NULL business 25,125.00 mod_cook 15,000.00 popular_comp 15,000.00 psychology 21,275.00 trad_cook 19,000.00 (6 rows affected) Always supply a name for any column in the select into result table that results from an aggregate function or any other expression. Examples are: • Arithmetic aggregates, for example, amount * 2 • Concatenation, for example, lname + fname • Functions, for example, lower(lname) Here is an example of using concatenation: select au_id, "Full_Name" = au_fname + ’ ’ + au_lnameCreating new tables from query results: select into 280 Adaptive Server Enterprise into #g_authortemp from authors where au_lname like "G%" (3 rows affected) select * from #g_authortemp au_id Full_Name ----------- ------------------------- 213-46-8915 Marjorie Green 472-27-2349 Burt Gringlesby 527-72-3246 Morningstar Greene (3 rows affected) Because functions allow null values, any column in the table that results from a function other than convert() or isnull() allows null values. Checking for errors select into is a two-step operation. The first step creates the new table and the second step inserts the specified rows into the table. Because select into operations are not logged, they cannot be issued within user-defined transactions and cannot be rolled back. If a select into statement fails after creating a new table, Adaptive Server does not automatically drop the table or deallocate its first data page. This means that any rows inserted on the first page before the error occurred remain on the page. Check the value of the @@error global variable after a select into statement to be sure that no error occurred. If an error occurs from a select into operation, drop table to remove the new table, then reissue the select into statement. Using select into with IDENTITY columns This section describes special rules for using the select into command with tables containing IDENTITY columns. Selecting an IDENTITY column into a new table To select an existing IDENTITY column into a new table, include the column name (or the syb_identity keyword) in the select statement’s column_list: CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 281 select column_list into table_name from table_name The following example creates a new table, stores_cal_pay30, based on columns from the stores_cal table: select record_id, stor_id, stor_name into stores_cal_pay30 from stores_cal where payterms = "Net 30" The new column inherits the IDENTITY property, unless any of the following conditions is true: • The IDENTITY column is selected more than once. • The IDENTITY column is selected as part of an expression. • The select statement contains a group by clause, aggregate function, union operator, or join. Selecting the IDENTITY column more than once A table cannot have more than one IDENTITY column. If an IDENTITY column is selected more than once, it is defined as NOT NULL in the new table. It does not inherit the IDENTITY property. In the following example, the record_id column, which is selected once by name and once by the syb_identity keyword, is defined as NOT NULL in stores_cal_pay60: select syb_identity, record_id, stor_id, stor_name into stores_cal_pay60 from stores_cal where payterms = "Net 60" Adding a new IDENTITY column with select into To define a new IDENTITY column in a select into statement, add the column definition before the into clause. The definition includes the column’s precision but not its scale: select column_list identity_column_name = identity(precision) into table_name from table_nameCreating new tables from query results: select into 282 Adaptive Server Enterprise The following example creates a new table, new_discounts, from the discounts table and adds a new IDENTITY column, id_col: select *, id_col=identity(5) into new_discounts from discounts If the column_list includes an existing IDENTITY column, and you add a description of a new IDENTITY column, the select into statement fails. Defining a column whose value must be computed IDENTITY column values are generated by Adaptive Server. New columns that are based on IDENTITY columns, but whose values must be computed rather than generated, cannot inherit the IDENTITY property. If a table’s select statement includes an IDENTITY column as part of an expression, the resulting column value must be computed. The new column is created as NULL if any column in the expression allows a NULL value. Otherwise, it is NOT NULL. In the following example, the new_id column, which is computed by adding 1000 to the value of record_id, is created NOT NULL: select new_id = record_id + 1000, stor_name into new_stores from stores_cal Column values are also computed if the select statement contains a group by clause or aggregate function. If the IDENTITY column is the argument of the aggregate function, the resulting column is created NULL. Otherwise, it is NOT NULL. IDENTITY columns selected into tables with unions or joins The value of the IDENTITY column uniquely identifies each row in a table. However, if a table’s select statement contains a union or join, individual rows can appear multiple times in the result set. An IDENTITY column that is selected into a table with a union or join does not retain the IDENTITY property. If the table contains the union of the IDENTITY column and a NULL column, the new column is defined as NULL. Otherwise, it is NOT NULL. For more information, see “Using IDENTITY columns” on page 247 and “Updating IDENTITY columns” on page 342. See also select in the Reference Manual. CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 283 Altering existing tables Use the alter table command to change the structure of an existing table. You can: • Add columns and constraints • Change column default values • Add either null or non-null columns • Drop columns and constraints • Change locking scheme • Partition or unpartition tables • Convert column datatypes • Convert the null default value of existing columns • Increase or decrease column length alter table includes the following syntax for modifying tables: alter table table_name [add column_name datatype [identity | null | not null] [, column_name datatype [identity |null | not null]]] [drop column_name [, column_name] [modify column_name {[data_type] [[null] | [not null]]} [, column_name datatype [null | not null]]] Where: • table_name is the table you are altering. • datatype is the datatype of the altered column. You must have the sa_role or be the object owner to run alter table. See the Reference Manual for the complete alter table syntax. For example, by default, the au_lname column of the authors table uses a varchar(50) datatype. To alter the au_lname to use a varchar(60), enter: alter table authors modify au_lname varchar(60) Note A variable cannot be used as the argument to a default that is part of an alter table statement.Altering existing tables 284 Adaptive Server Enterprise Dropping, modifying, and adding non-null columns may perform a data copy, which has implications for required space and the locking scheme. See “Data copying” on page 295. The modified table’s page chains inherits the table’s current configuration options (for example, if fillfactor is set to 50 percent, the new pages have this same fillfactor). Note Adaptive Server does partial logging (of page allocations) for alter table operations. However, because alter table is performed as a transaction, you cannot dump the transaction log after running alter table; you must dump the database to ensure it is recoverable. If the server encounters any problems during the alter table operation, Adaptive Server rolls back the transaction. alter table acquires an exclusive table lock while it is modifying the table schema. This lock is released as soon as the command is done. alter table does not fire any triggers. Objects using select * do not list changes to table If a database has any objects (stored procedures, triggers, and so on) that perform a select * on a table from which you have dropped a column, an error message lists the missing column. This occurs even if you create the objects using the with recompile option. For example, if you dropped the postalcode column from the authors table, any stored procedure that performed a select * on this table issues this error message: Msg 207, Level 16, State 4: Procedure ‘columns’, Line 2: Invalid column name ‘postalcode’. (return status = -6) This message does not appear if you add a new column and then run an object containing a select *; in this case, the new column does not appear in the output. You must drop and re-create any objects that reference a dropped column.CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 285 Using alter table on remote tables You can use alter table to modify a remote table using Component Integration Services (CIS). Before you modify a remote table, make sure that CIS is running by entering: sp_configure "enable cis" If CIS is enabled, the output of this command is “1.” By default, CIS is enabled when you install Adaptive Server. See the System Administration Guide for information about enabling configuration parameters. See the Component Integration Services User’s Guide for information about using CIS. Adding columns To add a column to an existing table, use: alter table table_name add column_name datatype [default {constant_expression} | user | null}] {[{identity | null | not null}] | [constraint constraint_name {constraint_clause}] [, column_name] Where: • table_name is the table to which you are adding a column. • column_name is the column you are adding. • constant_expression is the constant you want placed in the row if a user does not specify a value (this value must be in quotes, unless the character type is int, tinyint, smallint, numeric, or decimal). • constraint_name is the constraint you are adding to the table. • constraint_clause is the full text of the constraint you are adding. You can add any number of columns using a single alter table statement. For example, the following adds a non-null column named author_type, which includes the constant “primary_author” as the default value, and a null column named au_publisher to the authors table: alter table authors add author_type varchar(20) default "primary_author" not null, au_publisher varchar(40) nullAltering existing tables 286 Adaptive Server Enterprise Adding columns appends column IDs alter table adds a column to the table with a column ID that is one greater than the current maximum column ID. For example, Table 8-5 lists the default column IDs of the salesdetail table: Table 8-5: Column IDs of the salesdetail table This command appends the store_name column to the end of the salesdetail table with a column ID of 6: alter table salesdetail add store_name varchar(40) default “unknown” not null If you add another column, it will have a column ID of 7. Note Because a table’s column IDs change as columns are added and dropped, your applications should never rely on them. Adding NOT NULL columns You can add a NOT NULL column to a table. This means that a constant expression, and not a null value, is placed in the column when the column is added. This also ensures that, for all existing rows, the new column is populated with the specified constant expression when the table is created. Adaptive Server issues an error message if a user fails to enter a value for a NOT NULL column. The following adds the column owner to the stores table with a default value of “unknown:” alter table stores add owner_lname varchar(20) default "unknown" not null The default value can be a constant expression when adding NULL columns, but it can be a constant value only when adding a NOT NULL column (as in the example above). Column name stor_id ord_num title_id qty discount Col ID 1 2 3 4 5CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 287 Adding constraints To add a constraint to an existing column, use: alter table table_name add constraint constraint_name {constraint_clause} Where: • table_name is the name of the table to which you are adding a constraint. • constraint_name is the constraint you are adding. • constraint_clause is the rule the constrain enforces. For example, to add a constraint to the titles table that does not allow an advance in excess of 10,000: alter table titles add constraint advance_chk check (advance < 10000) If a user attempts to insert a value greater than 10,000 into the titles table, Adaptive Server produces an error message similar to this: Msg 548, Level 16, State 1: Line 1:Check constraint violation occurred, dbname = ‘pubs2’,table name= ‘titles’, constraint name = ‘advance_chk’. Command has been aborted. Adding a constraint does not affect the existing data. Also, if you add a new column with a default value and specify a constraint on that column, the default value is not validated against the constraint. For information about dropping a constraint, see “Dropping constraints” on page 289. Dropping columns Drop a column from an existing table using: alter table table_name drop column_name [, column_name] Where: • table_name is the table that contains the column you are dropping,. • column_name is the column you are dropping. Altering existing tables 288 Adaptive Server Enterprise You can drop any number of columns using a single alter table statement. However, you cannot drop the last remaining column from a table (for example, if you drop four columns from a five-column table, you cannot then drop the remaining column). For example, to drop the advance and the contract columns from the titles table: alter table titles drop advance, contract alter table rebuilds all indexes on the table when it drops a column. Dropping columns renumbers the column ID alter table renumbers column IDs when you drop a column from a table. Columns with IDs above the number of the dropped column move up one column ID to fill the gap that the dropped column leaves behind. For example, the titleauthor table contains these column names and column IDs: Table 8-6: titleauthor column IDs If you drop the au_ord column from the table: alter table titleauthor drop au_ord titleauthor now has these column names and column IDs: Table 8-7: Column IDs after dropping au_ord The royaltyper column now has the column ID of 3. The nonclustered index on both title_id and royaltyper are also rebuilt when au_ord is dropped. Also, all instances of column IDs in different system catalogs are renumbered. You will not generally notice the renumbering of column IDs. Note Because a table’s column IDs are renumbered as columns are added and dropped, your applications should never rely on them. If you have stored procedures or applications that depend on column IDs, you must rewrite these so they access the correct column IDs. Column Name au_id title_id au_ord royaltyper Column ID 1 2 3 4 Column Name au_id title_id royaltyper Column ID 1 2 3CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 289 Dropping constraints To drop a constraint, use: alter table table_name drop constraint constraint_name table_name and constraint_name have the same values as described in Adding constraintsabove. For example, to drop the constraint created above: alter table titles drop constaint advance_chk To find detailed information about a table’s constraints, see “Using sp_helpconstraint to find a table’s constraint information” on page 307. Modifying columns To modify an existing column, use: alter table table_name modify column_name datatype [null | not null] [null | not null] [, column_name...] Where: • table_name is the table that contains the column you are modifying. • column_name is the column you are modifying. • data_type is the datatype to which you are modifying the column. You can modify any number of columns in a single alter table statement. For example, this command changes the datatype of the type column in the titles table from char(12) to varchar(20) and makes it nullable: alter table titles modify type varchar(20) null Warning! You may have objects (stored procedures, triggers, and so on) that depend on a column having a particular datatype. Before you modify a column, make sure that any objects that reference it will be able to run successfully after the modification. Use sp_depends to determine a table’s dependent objects.Altering existing tables 290 Adaptive Server Enterprise Which datatypes can I convert? You can only convert datatypes that are either implicitly or explicitly convertible to the new datatype, or if there is an explicit conversion function in Transact-SQL. See the Reference Manual for a list of the supported datatype conversions. If you attempt an illegal datatype modification, Adaptive Server raises an error message and the operation is aborted. Note You cannot convert an existing column datatype to the timestamp datatype, nor can you modify a column that uses the timestamp datatype to any other datatype. If you issue the same alter table command more than once, Adaptive Server issues a message similar to this: Warning: ALTER TABLE operation did not affect column ‘au_lname’. Msg 13905, Level 16, State 1: Server ‘SYBASE1’, Line 1: Warning: no columns to drop, add or modify. ALTER TABLE ‘authors’ was aborted. Modifying tables may prevent successful bulk copy of previous dump Modifying either the length or datatype of a column may prevent you from successfully using bulk copy to copy in older dumps of the table. The older table schema may not be compatible with the new table schema. Before you modify a column’s length or datatype, verify that it will not prevent you from copying in a previous dump of the table. Decreasing column length may truncate data If you decrease the length of a column, make sure the reduced column length does not result in truncated data. For example, you could use alter table to reduce the length of the title column of the titles table from a varchar(80) to a varchar(2), but the data is meaningless: select title from titles title ----- Bu Co Co EmCHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 291 Fi Is Li Ne On Pr Se Si St Su Th Th Th Yo Adaptive Server issues error messages about truncating the column data only if the set string_rtruncation option is turned on. If you need to truncate character data, set the appropriate string-truncation option and modify the column to decrease its length. Modifying datetime columns If you modify a column from a char datatype to datetime, smalldatetime or date, you cannot specify the order that the month, day, and year appear in the output. Nor can you specify the language used in the output. Instead, both of these settings are given a default value. However, you can use set dateformat or set language to alter the output to match the setting of the information stored in the column. Also, Adaptive Server does not support modifying a column from smalldatetime to char datatype. See the Reference Manual for more information. Modifying the NULL default value of a column If you are changing only the NULL default value of a column, you do not need to specify a column’s datatype. For example, this command modifies the address column in the authors table from NULL to NOT NULL: alter table authors modify address not nullAltering existing tables 292 Adaptive Server Enterprise If you modify a column and specify the datatype as NOT NULL, the operation succeeds as long as none of the rows have NULL values. If, however, any of the rows have a NULL value, the operation fails and any incomplete transactions are rolled back. For example, the following statement fails because the titles table contains NULL values for the The Psychology of Computer Cooking: alter table titles modify advance numeric(15,5) not null Attempt to insert NULL value into column ‘advance’, table ‘pubs2.dbo.titles’; column does not allow nulls. Update fails. Command has been aborted. To run this command successfully, update the table to change all NULL values of the modified column to NOT NULL, then reissue the command. Modifying columns that have precision or scale Check the length of your data before you modify the column’s scale. If an alter table command causes a column value to lose precision (say from numeric(10,5) to numeric(5,5)), Adaptive Server aborts the statement. If this statement is part of a batch, the batch is aborted if the option is turned on. If an alter table command causes a column value to lose scale (say from numeric(10, 5) to numeric(10,3), the rows are truncated without warning. This occurs whether or not arithabort numeric_truncation is on or off. If arithignore arith_overflow is on and alter table causes a numeric overflow, Adaptive Server issues a warning. However, if arithignore arith_overflow is off, Adaptive Server does not issue a warning if alter table causes a numeric overflow. By default, arithignore arith_overflow is off when you install Adaptive Server. Note Make sure you review the data truncation rules and fully understand their implications before issuing commands that may truncate the length of the columns in your production environment. You should first perform the commands on a set of test columns. Modifying text and image columns text columns can only be converted to:CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 293 • nchar • varchar image columns can only be converted to: • varbinary • binary You cannot modify char or varchar datatype columns to text columns. If you are converting from text to char or varchar, the maximum length of the column is governed by page size. If you do not specify a column length, alter table uses the default length of one byte. If you are modifying a multibyte character text or image column, and you do not specify a column length that is sufficient to contain the data, Adaptive Server truncates the data to fit the column length. Adding, dropping, and modifying IDENTITY columns This section describes adding, dropping, and modifying IDENTITY columns using alter table. For a general discussion of IDENTITY columns, see “Using IDENTITY columns” on page 247. Adding IDENTITY columns You can add IDENTITY columns only with a default value of NOT NULL. You cannot specify a default clause for a new IDENTITY column. To add an IDENTITY column to a table, specify the identity keyword in the alter table statement: alter table table_name add column_name numeric(precision ,0) identity not null The following example adds an IDENTITY column, record_id, to the stores table: alter table stores add record_id numeric(5,0) identity not null When you add an IDENTITY column to a table, Adaptive Server assigns a unique sequential value, beginning with the value 1, to each row. If the table contains a large number of rows, this process can be time consuming. If the number of rows exceeds the maximum value allowed for the column (in this case, 10 5 - 1, or 99,999), the alter table statement fails. Altering existing tables 294 Adaptive Server Enterprise Dropping IDENTITY columns You can drop IDENTITY columns just like any other column. For example, to drop the IDENTITY column created in the previous section: alter table stores drop record_id However, the following restrictions apply to dropping an identity column: • If sp_dboption “identity in nonunique index” is turned on in the database. You must first drop all indexes, then drop the IDENTITY column, and then re-create the indexes. If the IDENTITY column is hidden, you must first identify it using the syb_identity keyword. See “Referring to IDENTITY columns with syb_identity” on page 250. • To drop an IDENTITY column from a table that has set identity_insert turned on, first issue sp_helpdb to determine if set identity_insert is turned on. You must turn off the set identity_insert option by issuing: set identity_insert table_name off Drop the IDENTITY column, then add the new IDENTITY column, and turn on the set identity_insert option by entering: set identity_insert table_name on Modifying IDENTITY columns You can modify the size of an IDENTITY column to increase its range. This might be necessary if either your current range is too small, or the range was used up because of a server shutdown. For example, you can increase the range of record_id by entering: alter table stores modify record_id numeric(9,0) You can decrease the range by specifying a smaller precision for the target datatype. Note that if the IDENTITY value in the table is too large for the range of the target IDENTITY column, an arithmetic conversion is raised and alter table aborts the statement.CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 295 You cannot add a non-null IDENTITY column to a partitioned table using alter table commands that require a data copy. Data copy is done in parallel for partitioned tables, and cannot guarantee unique IDENTITY values. Data copying Adaptive Server performs a data copy only if it must temporarily copy data out of a table before it changes the table’s schema. If the table has any indexes, Adaptive Server rebuilds the indexes when the data copy finishes. Note If alter table is performing a data copy, the database that contains the table must have select into/bulkcopy/pllsort turned on. See the Reference Manual for information about this option. Adaptive Server performs a data copy when: • You drop a column. • You modify any of these properties of a column: • The datatype (except when you increase the length of varchar, varbinary, or NULL char or NULL binary columns. • From NULL to NOT NULL, or vice-versa. • Decrease length. If you decrease a column’s length, you may not know beforehand if all the data will fit in the reduced column length. For example, if you decrease au_lname to a varchar(30), it may contain a name that requires a varchar(35). When you decrease a column’s data length, Adaptive Server first performs a data copy to ensure that the change in the column length is successful. • You increase the length of a number column (for example, from tinyint to int). Adaptive Server performs data copying in case one row has a NOT NULL value for this column. • You add a NOT NULL column. alter table does not perform a data copy when: • You change the length of either a varchar or a varbinary column.Altering existing tables 296 Adaptive Server Enterprise • You change the user-defined datatype ID but the physical datatype does not change. For example, if your site has two datatypes mychar1 and mychar2 that have different user-defined datatypes but the same physical datatype, data copy does not happen if you change mychar1 to mychar2. • You change the NULL default value of a variable length column from NOT NULL to NULL. To identify if alter table performs a data copy: 1 Set showplan on to report whether Adaptive Server will perform a data copy. 2 Set noexec on to ensure that no work will be performed. 3 Perform the alter table command if no data copy is required, only catalog updates are performed to reflect the changes made by the alter table command. Changing exp_row_size If you perform a data copy, you can also change the exp_row_size, which allows you to specify how much space to allow per row. You can change the exp_row_size only if the modified table schema contains variable length columns, and only to within the range specified by the maxlen and minlen values in sysindexes for the modified table schema. If the column has fixed-length columns, you can change the exp_row_size to only 0 or 1. If you drop all the variable-length columns from a table, you must specify an exp_row_size of 0 or 1. Also, if you do not supply an exp_row_size with the alter table command, the old exp_row_size is used. Adaptive Server raises an error if the table contains only fixed-length columns and the old exp_row_size is not compatible with the modified schema. You cannot use the exp_row_size clause with any of the other alter table subclauses (for example, defining a constraint, changing the locking scheme, and so on). You can also use sp_chgattribute to change the exp_row_size. For more information about changing the exp_row_size for both alter table and sp_chgattribute, see the Reference Manual.CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 297 Modifying locking schemes and table schema If alter table performs a data copy, you can also include a command to change the locking scheme of a table. For example, to modify the au_lname column of the authors table and change the locking scheme of the table from allpages locking to datarows locking: alter table authors modify au_lname varchar(10) lock datarows However, you cannot use alter table to change table schema and the locking scheme of a table that has a clustered index. If a table has a clustered index you can: 1 Drop the index. 2 Modify the table schema and change the locking scheme in the same statement (if the change in the table schema also includes a data copy). 3 Rebuild the clustered index. Alternately, you can issue an alter table command to change the locking scheme, then issue another alter table command to change the table’s schema. Altering columns with user defined datatypes You can use alter table to add, drop, or modify columns that use user-defined datatypes. Adding a column with user-defined datatypes Use the same syntax to add a column with a user-defined datatype as with a system-defined datatype. For example, to add a column to the authors table of pubs2 using the usertype datatype: alter table titles add newcolumn usertype not null The NULL or NOT NULL default you specify takes precedence over the default specified by the user-defined datatype. That is, if you add a column and specify NOT NULL as the default, the new column has a default of NOT NULL even if the user-defined datatype specifies NULL. If you do not specify NULL or NOT NULL, the default specified by the user-defined datatype is used. Altering existing tables 298 Adaptive Server Enterprise You must supply a default clause when you add columns that are not null, unless the user-defined datatype already has a default bound to it. If the user-defined datatype specifies IDENTITY column properties (precision and scale), the column is added as an IDENTITY column. Dropping a column with user-defined datatypes Drop a column with a user-defined datatype the same as you drop a column with a system-defined datatype. Modifying a column with user-defined datatypes The syntax to modify a column to include user-defined datatypes is the same as modifying a column to include system-defined datatypes. For example, to modify the au_lname of the authors table to use the user-defined newtype datatype: alter table authors modify au_lname newtype(60) not null If you do not specify either NULL or NOT NULL as the default, columns use the default specified by the user-defined datatype. Modifying the table does not affect any current rules or defaults bound to the column. However, if you specify new rules or defaults, any old rules or defaults bound to the user-defined datatype are dropped. If there are no previous rules or defaults bound to the column, any user-defined rules and defaults are applied. You cannot modify an existing column to an IDENTITY column. You can only modify an existing IDENTITY column with user-defined datatypes that have IDENTITY column properties (precision and scale). Errors and warnings from alter table Most errors you encounter when running alter table inform you of schema constructs that prevent the requested command (for example, if you try to drop a column that is part of an index). You must fix the errors or warnings that refer to schema objects that depend on the affected column before you reissue the command. To report error conditions: 1 Set showplan on.CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 299 2 Set noexec on. 3 Perform the alter table command. After you have changed the command to address any reported errors, set showplan and noexec to off so that Adaptive Server actually performs the work. alter table detects and reports certain errors when actually running the command (for example, if you are dropping a column, the presence of a referential constraint). All runtime data-dependent errors (for example, errors of numeric overflow, character truncation, and so on) can be identified only when the statement is executed. You must change the command to fit the data available, or fix the data value(s) to work with the required target datatypes the statement specifies. To identify these errors, you will have to run the command with noexec turned off. Errors and warnings generated by alter table modify Certain errors are generated only by the alter table modify command. Although alter table modify is used to convert columns to compatible datatypes, alter table may issue errors if the columns you are converting have certain restrictions. Note Make sure you understand the implications of modifying a datatype before you issue the command. Generally, use alter table modify only to implicitly convert between convertible datatypes. This ensures that any hidden conversions required during processing of insert and update statements do not fail because of datatype incompatibility. For example, if you add a second_advance column to the titles table with a datatype of int, and create a clustered index on second_advance, you cannot then modify this column to a char datatype. This would cause the int values to be converted from integers (1, 2, 3) to strings (‘1’, ‘2’, ‘3’). When the index is rebuilt with sorted data, the data values are expected to be in sorted order. But in this example, the datatype has changed from int to char and is no longer in sorted order for the char datatype’s ordering sequence. So, the alter table command fails during the index rebuild phase. Be very cautious when choosing a new datatype for columns that are part of index key columns of clustered indexes. alter table modify must specify a target datatype that will not violate the ordering sequence of the modified data values after its data copy phase. Altering existing tables 300 Adaptive Server Enterprise alter table modify also issues a warning message if you modify the datatype to an incompatible datatype in a column that contains a constraint. For example, if you try to modify from datatype char to datatype int, and the column includes a constraint, alter table modify issues this warning: Warning: a rule or constraint is defined on column ‘new_col’ being modified. Verify the validity of rules and constraints after this ALTER TABLE operation. This warning indicates that there might be some datatype inconsistency in the value that the constraint expects and the modified datatype of the column new_col: Warning: column ‘new_col’ is referenced by one or more rules or constraints. Verify the validity of the rules/constraints after this ALTER TABLE operation. If you attempt to insert data that is a datatype char into this table, it fails with this message: Msg 257, Level 16, State 1: Line 1: Implicit conversion from datatype ‘CHAR’ to ‘INT’ is not allowed. Use the CONVERT function to run this query. The check constraint was defined to expect the column to be a datatype int, but the data being inserted is a datatype char. Furthermore, you cannot insert the data as type int because column now uses a datatype of char. The insert returns this message: Msg 257, Level 16, State 1: Line 1: Implicit conversion from datatype ‘INT’ to ‘CHAR’ is not allowed. Use the CONVERT function to run this query. The modify operation is very flexible, but must be used with caution. In general, modifying to an implicitly convertible datatype works without errors. Modifying to an explicitly convertible datatype may lead to inconsistencies in the tables schema. Use sp_depends to identify all column-level dependencies before modifying a column’s datatype. Scripts generated by if exists()...alter table Scripts that include constructs like the following may produce errors if the table described in the script does not include the specified column: if exists (select 1 from syscolumns where id = object_id("some_table") and name = "some_column") beginCHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 301 alter table some_table drop some_column end In this example, some_column must exist in some_table for the batch to succeed. If some_column exists in some_table, the first time you run the batch, alter table drops the column. On subsequent executions, the batch will not compile. Adaptive Server raises these errors while preprocessing this batch, which are similar to those that are raised when a normal select tries to access a nonexistent column. These errors are raised when you modify a table’s schema using clauses that require a data copy. If you add a null column, and use the above construct, Adaptive Server does not raise these errors. To avoid such errors when you modify a table’s schema, include alter table in an execute immediate command: if exists (select 1 from syscolumns where id = object_id("some_table") and name = "some_column") begin exec ("alter table some_table drop some_column") end Because the execute immediate statement is run only if the if exists() function succeeds, Adaptive Server does not raise any errors when it compiles this script. You also need to use the execute immediate construct for other uses of alter table, for example, to change the locking scheme, and for any other cases when the command does not require data copy. Renaming tables and other objects To rename tables and other database objects—columns, constraints, datatypes, views, indexes, rules, defaults, procedures, and triggers—use sp_rename. You must own an object to rename it. You cannot change the name of system objects or system datatypes. The Database Owner can change the name of any user’s objects. Also, the object whose name you are changing must be in the current database. To rename the database, use sp_renamedb. See sp_renamedb in the Reference Manual.Dropping tables 302 Adaptive Server Enterprise The syntax of sp_rename is: sp_rename objname, newname For example, to change the name of friends_etc to infotable: sp_rename friends_etc, infotable To rename a column, use: sp_rename "table.column", newcolumnname You must leave off the table name prefix from the new column name, or the new name will not be accepted. To change the name of an index, use: sp_rename "table.index", newindexname Do not include the table name in the new name. To change the name of the user datatype tid to t_id, use: exec sp_rename tid, "t_id" Renaming dependent objects When you rename objects, you must also change the text of any dependent procedure, trigger, or view to reflect the new object name. The original object name continues to appear in query results until you change the name of, and compile the procedure, trigger, or view. The safest course is to change the definitions of any dependent objects when you execute sp_rename. You can get a list of dependent objects using sp_depends. You can use the defncopy utility program to copy the definitions of procedures, triggers, rules, defaults, and views into an operating system file. Edit this file to correct the object names, then use defncopy to copy the definition back into Adaptive Server. For more information on defncopy, refer to The Utility Guide. Dropping tables Use drop table to remove a table from a database. drop table [[database.]owner.] table_name [, [[database.]owner.] table_name]... CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 303 This command removes the specified tables from the database, together with their contents and all indexes and privileges associated with them. Rules or defaults bound to the table are no longer bound, but are otherwise not affected. You must be the owner of a table in order to drop it. However, no one can drop a table while it is being read or written to by a user or a front-end program. You cannot use drop table on any system tables, either in the master database or in a user database. You can drop a table in another database as long as you are the table owner. If you delete all the rows in a table or use truncate table on it, the table exists until you drop it. drop table and truncate table permission cannot be transferred to other users. Assigning permissions to users The grant and revoke commands control the Adaptive Server command and object protection system. You can give various kinds of permissions to users, groups, and roles with the grant command and rescind them with the revoke command including: • Creating databases • Creating objects in a database • Accessing tables, views, and columns • Executing stored procedures Some commands can be used at any time by any user, with no permissions required. Others can be used only by users of certain status (for example, a System Administrator) and cannot be transferred. The ability to assign permissions for commands that can be granted and revoked is determined by each user’s status (as System Administrator, Database Owner, or database object owner) and by whether a particular user has been granted a permission with the option to grant that permission to other users. Assigning permissions to users 304 Adaptive Server Enterprise Database owners do not automatically receive permissions on objects that are owned by other users. But a Database Owner or System Administrator can acquire any permission by using the setuser command to temporarily assume the identity of the object owner, and then writing the appropriate grant or revoke statement. You can assign two kinds of permissions with grant and revoke: object access permissions and object creation permissions. Object access permissions regulate the use of certain commands that access certain database objects. For example, you must be granted permission to use the select command on the authors table. Object access permissions are granted and revoked by object owners. To grant Mary and Joe the object access permission to insert into and delete from the titles table: grant insert, delete on titles to mary, joe Object creation permissions regulate the use of commands that create objects. These permissions can be granted only by a System Administrator or Database Owner. For example, to revoke from Mary permission to create tables and rules in the current database: revoke create table, create rule from mary For complete information about using grant and revoke, see the System Administration Guide. A System Security Officer can also use roles to simplify the task of granting and revoking access permissions. For example, instead of having object owners grant privileges on each object individually to each employee, the System Security Officer can create roles, request object owners to grant privileges to each role, and grant these userdefined roles to individual employees, based on the functions they perform in the organization. The System Security Officer can also revoke user-defined roles granted to the employee. For complete information about user-defined roles, see the System Administration Guide.CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 305 Getting information about databases and tables Adaptive Server includes several procedures and functions you can use to get information about databases, tables, and other database objects. This section describes some of them. For complete information, see the Reference Manual. Getting help on databases sp_helpdb can report information about a specified database or about all Adaptive Server databases. It reports the name, size, and usage of each fragment you have assigned to the database. sp_helpdb [dbname] For example, to display a report on pubs2: sp_helpdb pubs2 name db_size owner dbid created status ----- ------- ------ ---- --------------- ------ ------- pubs2 2 MB sa 4 Jun 18 1997 no options set (1 row affected) device size usage ----------------- ----------- -------------- pubsdev 2 MB data + log (1 row affected) sp_databases lists all the databases on a server. For example: sp_databases database_name database_size remarks ----------------- ------------- ------------ master 5120 NULL model 2048 NULL pubs2 2048 NULL pubs3 2048 NULL sybsecurity 5120 NULL sybsystemprocs 30720 NULL tempdb 2048 NULL (7 rows affected, return status = 0) To find out who owns a database, use sp_helpuser:Getting information about databases and tables 306 Adaptive Server Enterprise sp_helpuser dbo Users_name ID_in_db Group_name Login_name ------------- -------- ------------ ------------ dbo 1 public sa (return status = 0) Use db_id() and db_name() to identify the current database. For example: select db_name(), db_id() ------------------------------ ------ master 1 Getting help on database objects Adaptive Server provides system procedures, catalog stored procedures, and built-in functions that return helpful information about database objects such as tables, columns, and constraints. Using sp_help on database objects Use sp_help to display information about a specified database object (that is, any object listed in sysobjects), a specified datatype (listed in systypes), or all objects and datatypes in the current database. sp_help [objname] Here is the output for the publishers table: Name Owner Type -------------------------- ----------- ---------- publisher dbo user table (1 row affected) Data_located_on_segment When_created ------------------------------ -------------------- default Jul 7 1997 1:43PM Column_name Type Length Prec Scale ----------- ------- ------ ----- ----- pub_id char 4 NULL NULL pub_name varchar 40 NULL NULL city varchar 20 NULL NULL state char 2 NULL NULLCHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 307 Nulls Default_name Rule_name Identity ----- ------------- --------- -------- 0 NULL pub_idrule 0 1 NULL NULL 0 1 NULL NULL 0 1 NULL NULL 0 index_name index_description index_keys index_max_rows_per_page ---------- ------------------ ---------- ------------ ----------- pubind clustered, unique pub_id 0 located on default (1 row affected) keytype object related_object related_keys ------- ---------- -------------- ------------ primary publishers -- none -- pub_id, *, *, *, *, * foreign titles publishers pub_id, *, *, *, *, * (1 row affected) Object is not partitioned. (return status = 0) If you execute sp_help without supplying an object name, the resulting report shows each object in sysobjects, along with its name, owner, and object type. Also shown is each user-defined datatype in systypes and its name, storage type, length, whether null values are allowed, and any defaults or rules bound to it. The report also notes if any primary or foreign key columns have been defined for a table or view. sp_help lists any indexes on a table, including those created by defining unique or primary key constraints. However, it does not describe any information about the integrity constraints defined for a table. Use sp_helpconstraint to display information about any integrity constraints. Using sp_helpconstraint to find a table’s constraint information sp_helpconstraint reports information about the declarative referential integrity constraints specified for a table, including the constraint name and definition of the default, unique or primary key constraint, referential, or check constraint. sp_helpconstraint also reports the number of references associated with the specified tables. Getting information about databases and tables 308 Adaptive Server Enterprise Its syntax is: sp_helpconstraint [objname] [, detail] objname is the name of the table being queried. If you do not include a table name, sp_helpconstraint displays the number of references associated with each table in the current database. With a table name, sp_helpconstraint reports the name, definition, and number of integrity constraints associated with the table. The detail option also returns information about the constraint’s user or error messages. For example, suppose you run sp_helpconstraint on the store_employees table in pubs3. name defn --------------------------- ------------------------- ------- store_empl_stor_i_272004000 store_employees FOREIGN KEY (stor_id) REFERENCES stores(stor_id) store_empl_mgr_id_288004057 store_employees FOREIGN KEY (mgr_id) SELF REFERENCES store_employees(emp_id) store_empl_2560039432 UNIQUE INDEX( emp_id) : NONCLUSTERED, FOREIGN REFERENCE (3 rows affected) Total Number of Referential Constraints: 2 Details: -- Number of references made by this table: 2 -- Number of references to this table: 1 -- Number of self references to this table: 1 Formula for Calculation: Total Number of Referential Constraints = Number of references made by this table + Number of references made to this table - Number of self references within this table To find the largest number of referential constraints associated with any table in the current database, run sp_helpconstraint without specifying a table name, for example: sp_helpconstraint id name CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 309 Num_referential_constraints ----------- ------------------------ ----------------- ---------- 80003316 titles 4 16003088 authors 3 176003658 stores 3 256003943 salesdetail 3 208003772 sales 2 336004228 titleauthor 2 896006223 store_employees 2 48003202 publishers 1 128003487 roysched 1 400004456 discounts 1 448004627 au_pix 1 496004798 blurbs 1 (11 rows affected) In this report, the titles table has the largest number of referential constraints in the pubs3 database. Finding out how much space a table uses Use sp_spaceused to find out how much space a table uses: sp_spaceused [objname] sp_spaceused computes and displays the number of rows and data pages used by a table or a clustered or nonclustered index. To display a report on the space used by the titles table: sp_spaceused titles name rows reserved data index_size unused ------- ----- --------- ----- --------- ------ titles 18 48 KB 6 KB 4 KB 38 KB (0 rows affected) If you do not include an object name, sp_spaceused displays a summary of space used by all database objects. Listing tables, columns, and datatypes Catalog stored procedures retrieve information from the system tables in tabular form. You can supply wildcard characters for some parameters. sp_tables lists all user tables in a database when used in the following format: Getting information about databases and tables 310 Adaptive Server Enterprise sp_tables @table_type = "’TABLE’" sp_columns returns the datatype of any or all columns in one or more tables in a database. You can use wildcard characters to get information about more than one table or column. For example, the following command returns information about all columns that includes the string “id” in all the tables with “sales” in their name: sp_columns "%sales%", null, null, "%id%" table_qualifier table_owner table_name column_name data_type type_name precision length scale radix nullable remarks ss_data_type colid --------------- ----------- ---------- ----------- --------- --------- --------- ------ ----- -- --- -------- ------- ------------ ----- pubs2 dbo sales stor_id 1 char 4 4 NULL NULL 0 NULL 47 1 pubs2 dbo salesdetail stor_id 1 char 4 4 NULL NULL 0 NULL 4 1 pubs dbo salesdetail title_id 12 varchar 6 6 NULL NULL 0 NULL 39 3 (3 rows affected, return status = 0)CHAPTER 8 Creating Databases and Tables Transact-SQL User’s Guide 311 Finding an object name and ID Use object_id() and object_name() to identify the ID and name of an object. For example: select object_id("titles") ---------- 208003772 Object names and IDs are stored in the sysobjects system table.Getting information about databases and tables 312 Adaptive Server EnterpriseTransact-SQL User’s Guide 313 C H A P T E R 9 Adding, Changing, and Deleting Data After you create a database, tables, and indexes, you can put data into the tables and work with it—adding, changing, and deleting data as necessary. This chapter covers the following topics: Introduction The commands you use to add, change, or delete data are called data modification statements. These commands are: • insert – adds new rows to a table. • update – changes existing rows in a table. • writetext – adds or changes text and image data without writing lengthy changes in the system’s transaction log. • delete – removes specific rows from a table. • truncate table – removes all rows from a table. For information about these commands, see the Reference Manual. You can also add data to a table by transferring it from a file using the bulk copy utility program bcp. See the Utility Guide for your platform for more information. Topic Page Introduction 313 Datatype entry rules 316 Adding new data 324 Changing existing data 337 Changing text and image data 342 Deleting data 343 Deleting all rows from a table 346Introduction 314 Adaptive Server Enterprise You can use insert, update, or delete to modify data in one table per statement. A Transact-SQL enhancement to these commands is that you can base modifications on data in other tables, and even other databases. The data modification commands also work on views, with some restrictions. See Chapter 10, “Views: Limiting Access to Data.” Permissions Data modification commands are not necessarily available to everyone. The Database Owner and the owners of database objects can use the grant and revoke commands to specify the users who have data modification functions. Permissions or privileges can be granted to individual users, groups, or the public for any combination of the data modification commands. Permissions are discussed in the System Administration Guide. Referential integrity insert, update, delete, writetext, and truncate table allow you to change data without changing related data in other tables, however, disparities may develop. For example, if you change the au_id entry for Sylvia Panteley in the authors table, you must also change it in the titleauthor table and in any other table in the database that has a column containing that value. If you do not, you cannot find information such as the names of Ms. Panteley’s books, because you cannot make joins on her au_id column. Keeping data modifications consistent throughout all tables in a database is called referential integrity. One way to manage it is to define referential integrity constraints for the table. Another way is to create special procedures called triggers that take effect when you give insert, update, and delete commands for particular tables or columns (the truncate table command is not caught by triggers or referential integrity constraints). See Chapter 17, “Triggers: Enforcing Referential Integrity”; and Chapter 8, “Creating Databases and Tables.” To delete data from referential integrity tables, change the referenced tables first and then the referencing table.CHAPTER 9 Adding, Changing, and Deleting Data Transact-SQL User’s Guide 315 Transactions A copy of the old and new state of each row affected by each data modification statement is written to the transaction log. This means that if you begin a transaction by issuing the begin transaction command, realize you have made a mistake, and roll the transaction back, the database is restored to its previous condition. Note You cannot roll back changes made on a remote Adaptive Server by means of a remote procedure call (RPC). An exception is writetext, when the select/into bulkcopy database option is set to false. The default mode of operation for writetext does not log the transactions. This avoids filling up the transaction log with the extremely long blocks of data that text and image fields may contain. The with log option to the writetext command must be used to log changes made with this command. A more complete discussion of transactions appears in Chapter 19, “Transactions: Maintaining Data Consistency and Recovery.” Using the sample databases If you follow the examples in this chapter, Sybase suggests that you start with a clean copy of the pubs2 or pubs3 database and return it to that state when you are finished. See a System Administrator for help in getting a clean copy of either of these databases. You can prevent any changes you make from becoming permanent by enclosing all the statements you enter inside a transaction, and then aborting the transaction when you are finished with this chapter. For example, start the transaction by typing: begin tran modify_pubs2 This transaction is named modify_pubs2. You can cancel the transaction at any time and return the database to the condition it was in before you began the transaction by typing: rollback tran modify_pubs2Datatype entry rules 316 Adaptive Server Enterprise Datatype entry rules Several of the Adaptive Server-supplied datatypes have special rules for entering and searching for data. For more information on datatypes, see Chapter 8, “Creating Databases and Tables.” char, nchar, unichar, univarchar, varchar, nvarchar, and text All character, text, date and time data must be enclosed in single or double quotes when you enter it as a literal. Use single quotes if the quoted_identifier option of the set command is set on. If you use double quotes, Adaptive Server treats the text as an identifier. Character literals may be any length, whatever the logical page size of the database. If the literal is wider than 16 kilobytes (16384 bytes), Adaptive Server treats it as text data, which has restrictive rules regarding implicit and explicit conversion to other datatypes. See the Reference Manual for a discussion of the different behavior of character and text datatypes. When you insert character data into a char, nchar, unichar, univarchar, varchar, or nvarchar column whose specified length is less than the length of the data, the entry is truncated. Set the string_rtruncation option on to receive a warning message when this occurs. Note This truncation rule applies to all character data, whether it resides in a column, a variable, or a literal string. There are two ways to specify literal quotes within a character entry: • Use two quotes. For example, if you begin a character entry with a single quote and you want to include a single quote as part of the entry, use two single quotes: ’I don’t ’understand.’’ For double quotes: “He said, ““It’s not really confusing.””” • Enclose the quoted material in the opposite kind of quotation mark. In other words, surround an entry containing a double quote with single quotes, or vice versa. For example: ’George said, “There must be a better way.” ’ To enter a character string that is longer than the width of your screen, enter a backslash (\) before going to the next line. CHAPTER 9 Adding, Changing, and Deleting Data Transact-SQL User’s Guide 317 Use the like keyword and wildcard characters described in Chapter 2, “Queries: Selecting Data from a Table,” to search for character, text, and datetime data. See the Reference Manual for details on inserting text data and information about trailing blanks in character data. date and time data types Adaptive Server allows datatypes datetime, smalldatetime, date and time. Display and entry formats for datetime data provide a wide range of date output formats, and recognize a variety of input formats. The display and entry formats are controlled separately. The default display format provides output that looks like “Apr 15 1997 10:23PM”. The convert command provides options to display seconds and milliseconds and to display the date with other date-part ordering. See Chapter 11, “Using the Built-In Functions in Queries,” for more information on displaying date values. Adaptive Server recognizes a wide variety of data entry formats for dates. Case is always ignored, and spaces can occur anywhere between date parts. When you enter datetime and smalldatetime values, always enclose them in single or double quotes. Use single quotes if the quoted_identifier option is on; if you use double quotes, Adaptive Server treats the entry as an identifier. Adaptive Server recognizes the two date and time portions of the data separately, so the time can precede or follow the date. Either portion can be omitted, in which case Adaptive Server uses the default. The default date and time is January 1, 1900, 12:00:00:000AM. For datetime, the earliest date you can use is January 1, 1753; the latest is December 31, 9999. For smalldatetime, the earliest date you can use is January 1, 1900; the latest is June 6, 2079. Dates earlier or later than these dates must be entered, stored, and manipulated as char, or unichar; or varchar or univarchar values. Adaptive Server rejects all values it cannot recognize as dates between those ranges. For date, the earliest date you can use is Januarry 1, 0001 through December 31, 9999. Dates earlier or later than these dates must be entered, stored, and manipulated as char, or unichar; or varchar or univarchar values. Adaptive Server rejects all values it cannot recognize as dates between those ranges. For time, the earliest time is 12:00AM through 11:59:59:999.Datatype entry rules 318 Adaptive Server Enterprise Entering times The order of time components is significant for the time portion of the data. First, enter the hours; then minutes; then seconds; then milliseconds; then AM (or am) or PM (pm). 12AM is midnight; 12PM is noon. To be recognized as time, a value must contain either a colon or an AM or PM signifier. smalldatetime is accurate only to the minute. time is accurate to the millesecond. Milliseconds can be preceded by either a colon or a period. If preceded by a colon, the number means thousandths of a second. If preceded by a period, a single digit means tenths of a second, two digits mean hundredths of a second, and three digits mean thousandths of a second. For example, “12:30:20:1” means 20 and one-thousandth of a second past 12:30; “12:30:20.1” means 20 and one-tenth of a second past 12:30. Among the acceptable formats for time data are: 14:30 14:30[:20:999] 14:30[:20.9] 4am 4 PM [0]4[:30:20:500]AM Entering dates The set dateformat command specifies the order of the date parts (month, day, and year) when dates are entered as strings of numbers with separators. set language can also affect the format for dates, depending on the default date format for the language you specify. The default language is us_english, and the default date format is mdy. See the set command in the Reference Manual for more information. Note dateformat affects only the dates entered as numbers with separators, such as “4/15/90” or “20.05.88”. It does not affect dates where the month is provided in alphabetic format, such as “April 15, 1990” or where there are no separators, such as “19890415”. Date formats Adaptive Server recognizes three basic date formats, as described below. Each format must be enclosed in quotes and can be preceded or followed by a time specification, as described under “Entering times” on page 318. CHAPTER 9 Adding, Changing, and Deleting Data Transact-SQL User’s Guide 319 • The month is entered in alphabetic format. • Valid formats for specifying the date alphabetically are: Apr[il] [15][,] 1997 Apr[il] 15[,] [19]97 Apr[il] 1997 [15] [15] Apr[il][,] 1997 15 Apr[il][,] [19]97 15 [19]97 apr[il] [15] 1997 apr[il] 1997 APR[IL] [15] 1997 [15] APR[IL] • Month can be a three-character abbreviation, or the full month name, as given in the specification for the current language. • Commas are optional. • Case is ignored. • If you specify only the last two digits of the year, values of less than 50 are interpreted as “20yy”, and values of 50 or more are interpreted as “19yy”. • Type the century only when the day is omitted or when you need a century other than the default. • If the day is missing, Adaptive Server defaults to the first day of the month. • When you specify the month in alphabetic format, the dateformat setting is ignored (see the set command in the Reference Manual). • The month is entered in numeric format, in a string with a slash (/), hyphen (-), or period (.) separator. • The month, day, and year must be specified. • The strings must be in the form: [ ] or: [ ] Datatype entry rules 320 Adaptive Server Enterprise • The interpretation of the values of the date parts depends on the dateformat setting. If the ordering does not match the setting, either the values will not be interpreted as dates, because the values are out of range, or the values will be misinterpreted. For example, “12/10/08” could be interpreted as one of six different dates, depending on the dateformat setting. See the set command in the Reference Manual for more information. • To enter “April 15, 1997” in mdy dateformat, you can use these formats: [0]4/15/[19]97 [0]4-15-[19]97 [0]4.15.[19]97 • The other entry orders are shown below with ‘‘/” as a separator; you can also use hyphens or periods: 15/[0]4/[19]97 (dmy) 1997/[0]4/15 (ymd) 1997/15/[0]4 (ydm) [0]4/[19]97/15 (myd) 15/[19]97/[0]4 (dym) • The date is given as an unseparated four-, six-, or eight-digit string, or as an empty string, or only the time value, but no date value, is given. • The dateformat is always ignored with this entry format. • If four digits are given, the string is interpreted as the year, and the month is set to January, the day to the first of the month. The century cannot be omitted. • Six- or eight-digit strings are always interpreted as ymd; the month and day must always be two digits. This format is recognized: [19]960415. • An empty string (“”) or missing date is interpreted as the base date, January 1, 1900. For example, a time value like “4:33” without a date is interpreted as “January 1, 1900, 4:33AM’’.CHAPTER 9 Adding, Changing, and Deleting Data Transact-SQL User’s Guide 321 The set datefirst command specifies the day of the week (Sunday, Monday, and so on) when weekday or dw is used with datename, and a corresponding number when used with datepart. Changing the language with set language can also affect the format for dates, depending on the default first day of the week value for the language. For the default language of us_english, the default datefirst setting is Sunday=1, Monday=2, and so on; others produce Monday=1, Tuesday=2, and so on. The default behavior can be changed on a per-session basis with set datefirst. See the set command in the Reference Manual for more information. Searching for dates and times You can use the like keyword and wildcard characters with datetime, smalldatetime, date and time data as well as with char, unichar, nchar, varchar, univarchar, nvarchar, and text. When you use like with date and time values, Adaptive Server first converts the dates to the standard date/time format and then converts them to varchar or univarchar. Since the standard display formats for datetime and smalldatetime does not include seconds or milliseconds, you cannot search for seconds or milliseconds with like and a match pattern. Use the type conversion function, convert, to search for seconds and milliseconds. It is a good idea to use like when you search for datetime or smalldatetime values, because datetime or smalldatetime entries may contain a variety of date parts. For example, if you insert the value “9:20” into a column named arrival_time, the following clause would not find it because Adaptive Server converts the entry to “Jan 1, 1900 9:20AM”: where arrival_time = "9:20" However, this clause would find it: where arrival_time like "%9:20%" This holds true when using date and time datatypes as well. If you are using like, and the day of the month is less than 10, you must insert two spaces between the month and day to match the varchar conversion of the datetime value. Similarly, if the hour is less than 10, the conversion places two spaces between the year and the hour. The clause like May 2%, with one space between “May” and “2”, will find all dates from May 20 through May 29, but not May 2. You do not need to insert the extra space with other date comparisons, only with like, since the datetime values are converted to varchar only for the like comparison. Datatype entry rules 322 Adaptive Server Enterprise binary, varbinary, and image When you enter binary, varbinary, or image data as literals, you must precede the data by “0x”. For example, to enter “FF”, type “0xFF”. Do not, however, enclose data beginning with “0x” with quotation marks. Binary literals may be any length, whatever the logical page size of the database. If the length of the literal is less than 16 kilobytes (16384 bytes), Adaptive Server treats the literal as varbinary data. If the length of the literal is greater than 16 kilobytes, Adaptive Server treats it as image data. See the Reference Manual for the different behaviors of binary datatypes and image datatypes. When you insert binary data into a column whose specified length is less than the length of the data, the entry is truncated without warning. A length of 10 for a binary or varbinary column means 10 bytes, each storing 2 hexadecimal digits. When you create a default on a binary or varbinary column, precede it with “0x”. See the Reference Manual for information on trailing zeros in hexadecimal values. money and smallmoney Monetary values entered with the E notation are interpreted as float. This may cause an entry to be rejected or to lose some of its precision when it is stored as a money or smallmoney value. money and smallmoney values can be entered with or without a preceding currency symbol such as the dollar sign ($), yen sign (¥) or pound sterling sign (£). To enter a negative value, place the minus sign after the currency symbol. Do not include commas in your entry. You cannot enter money or smallmoney values with commas, although the default print format for money or smallmoney data places a comma after every three digits. When money or smallmoney values are displayed, they are rounded up to the nearest cent. All the arithmetic operations except modulo are available with money. CHAPTER 9 Adding, Changing, and Deleting Data Transact-SQL User’s Guide 323 float, real, and double precision You enter the approximate numeric types—float, real, and double precision—as a mantissa followed by an optional exponent. The mantissa can include a positive or negative sign and a decimal point. The exponent, which begins after the character “e” or “E”, can include a sign but not a decimal point. To evaluate approximate numeric data, Adaptive Server multiplies the mantissa by 10 raised to the given exponent. Table 9-1 shows examples of float, real, and double precision data: Table 9-1: Evaluating numeric data The column’s binary precision determines the maximum number of binary digits allowed in the mantissa. For float columns, you can specify a precision of up to 48 digits; for real and double precision columns, the precision is machine-dependent. If a value exceeds the column’s binary precision, Adaptive Server flags the entry as an error. decimal and numeric The exact numeric types—dec, decimal, and numeric—begin with an optional positive or negative sign and can include a decimal point. The value of exact numeric data depends on the column’s decimal precision and scale, which you specify using this syntax: datatype [(precision [, scale ])] Adaptive Server treats each combination of precision and scale as a distinct datatype. For example, numeric (10,0) and numeric (5,0) are two separate datatypes. The precision and scale determine the range of values that can be stored in a decimal or numeric column: • The precision specifies the maximum number of decimal digits that can be stored in the column. It includes all digits to the right and left of the decimal point. You can specify a precision ranging from 1 to 38 digits or use the default precision of 18 digits. Data Entered Mantissa Exponent Value 10E2 10 2 10 * 10 2 15.3e1 15.3 1 15.3 * 10 1 -2.e5 -2 5 -2 * 10 5 2.2e-1 2.2 -1 2.2 * 10 -1 +56E+2 56 2 56 * 10 2Adding new data 324 Adaptive Server Enterprise • The scale specifies the maximum number of digits that can be stored to the right of the decimal point. The scale must be less than or equal to the precision. You can specify a scale ranging from 0 to 38 digits or use the default scale of 0 digits. If a value exceeds the column’s precision or scale, Adaptive Server flags the entry as an error. Here are some examples of valid dec and numeric data: Table 9-2: Valid precision and scale for numeric data The following entries result in errors because they exceed the column’s precision or scale: Table 9-3: Invalid precision and scale for numeric data int, smallint, and tinyint You can insert numeric values into int, smallint, and tinyint columns with the E notation, as described in the preceding section. timestamp You cannot insert data into a timestamp column. You must either insert an explicit null by typing “NULL” in the column or use an implicit null by providing a column list that skips the timestamp column. Adaptive Server updates the timestamp value after each insert or update. See “Inserting data into specific columns” on page 326 for more information. Adding new data You can use the insert command to add rows to the database in two ways; with the values keyword or with a select statement: Data Entered Datatype Precision Scale Value 12.345 numeric(5,3) 5 3 12.345 -1234.567 dec(8,4) 8 4 -1234.567 Data Entered Datatype Precision Scale 1234.567 numeric(3,3) 3 3 1234.567 decimal(6) 6 1CHAPTER 9 Adding, Changing, and Deleting Data Transact-SQL User’s Guide 325 • The values keyword specifies values for some or all of the columns in a new row. A simplified version of the syntax for the insert command using the values keyword is: insert table_name values (constant1, constant2, ...) • You can use a select statement in an insert statement to pull values from one or more tables (up to a limit of 16 tables, including the table into which you are inserting). A simplified version of the syntax for the insert command using a select statement is: insert table_name select column_list from table_list where search_conditions insert syntax Here is the full syntax for the insert command: insert [into] [database.[owner.]] {table_name | view_name} [(column_list)] {values (constant_expression [, constant_expression]...) | select_statement} Note When you add text or image values with insert, all the data is written to the transaction log. You can use the writetext command to add these values without logging the long chunks of data that may comprise text or image values. See “Inserting data into specific columns” on page 326 and “Changing text and image data” on page 342. Adding new rows with values This insert statement adds a new row to the publishers table, giving a value for every column in the row: insert into publishers values ("1622", "Jardin, Inc.", "Camden", "NJ") Notice that the data values are typed in the same order as the column names in the original create table statement, that is, first the ID number, then the name, then the city, and, finally, the state. The values data is surrounded by parentheses and all character data is enclosed in single or double quotes. Adding new data 326 Adaptive Server Enterprise Use a separate insert statement for each row you add. Inserting data into specific columns You can add data to some columns in a row by specifying only those columns and their data. All other columns that are not included in the column list must be defined to allow null values. The skipped columns can accept defaults. If you skip a column that has a default bound to it, the default is used. You may especially want to use this form of the insert command to insert all of the values in a row except the text or image values, and then use writetext to insert the long data values so that these values are not stored in the transaction log. You can also use this form of the command to skip over timestamp data. Adding data in only two columns, for example, pub_id and pub_name, requires a command like this: insert into publishers (pub_id, pub_name) values ("1756", "The Health Center") The order in which you list the column names must match the order in which you list the values. The following example produces the same results as the previous one: insert publishers (pub_name, pub_id) values("The Health Center", "1756") Either of the insert statements places “1756” in the identification number column and “The Health Center” in the publisher name column. Since the pub_id column in publishers has a unique index, you cannot execute both of these insert statements; the second attempt to insert a pub_id value of “1756” produces an error message. The following select statement shows the row that was added to publishers: select * from publishers where pub_name = "The Health Center" pub_id pub_name city state ------- ----------------- ------ ------- 1756 The Health Center NULL NULL Adaptive Server enters null values in the city and state columns because no value was given for these columns in the insert statement, and the publisher table allows null values in these columns. CHAPTER 9 Adding, Changing, and Deleting Data Transact-SQL User’s Guide 327 Restricting column data: rules You can create a rule and bind it to a column or user-defined datatype. Rules govern the kind of data that can or cannot be added. The pub_id column of the publishers table is an example. A rule called pub_idrule, which specifies acceptable publisher identification numbers, is bound to the column. The acceptable IDs are “1389”, “0736”, “0877”, “1622”, and “1756” or any four-digit number beginning with “99”. If you enter any other number, you get an error message. When you get this kind of error message, you may want to use sp_helptext to look at the definition of the rule: : sp_helptext pub_idrule --------- 1 (1 row affected) text --------------------------------------------------- create rule pub_idrule as @pub_id in ("1389", "0736", "0877", "1622", "1756") or @pub_id like "99[0-9][0-9]" (1 row affected) For more general information on a specific rule, use sp_help. Or use sp_help with a table name as a parameter to find out if any of the columns has a rule. See Chapter 13, “Defining Defaults and Rules for Data.” Using the NULL character string Only columns for which NULL was specified in the create table statement and into which you have explicitly entered NULL (no quotes), or into which no data has been entered, contain null values. Avoid entering the character string “NULL” (with quotes) as data for a character column. It can only lead to confusion. Use “N/A” or “none” or a similar value instead. When you want to enter the value NULL explicitly, do not use single or double quotes. To explicitly insert NULL into a column: values({expression | null} [, {expression | null}]...)Adding new data 328 Adaptive Server Enterprise The following example shows two equivalent insert statements. In the first statement, the user explicitly inserts a NULL into column t1. In the second, Adaptive Server provides a NULL value for t1because the user has not specified an explicit column value: create table test (t1 char(10) null, t2 char(10) not null) insert test values (null, "stuff") insert test (t2) values ("stuff") NULL is not an empty string The empty string (“ ”or ‘ ’) is always stored as a single space in variables and column data. This concatenation statement is equivalent to “abc def”, not “abcdef”: "abc" + "" + "def" The empty string is never evaluated as NULL. Inserting NULLs into columns that do not allow them To insert data with select from a table that has null values in some fields into a table that does not allow null values, you must provide a substitute value for any NULL entries in the original table. For example, to insert data into an advances table that does not allow null values, this example substitutes “0” for the NULL fields: insert advances select pub_id, isnull(advance, 0) from titles Without the isnull function, this command inserts all the rows with non-null values into advances and produces error messages for all the rows where the advance column in titles contains NULL. If you cannot make this kind of substitution for your data, you cannot insert data containing null values into columns with a NOT NULL specification. Adding rows without values in all columns When you specify values for only some of the columns in a row, one of four things can happen to the columns with no values: CHAPTER 9 Adding, Changing, and Deleting Data Transact-SQL User’s Guide 329 • If a default value exists for the column or user-defined datatype of the column it is entered. See Chapter 13, “Defining Defaults and Rules for Data,” or create default in the Reference Manual for details. • If NULL was specified for the column when the table was created and no default value exists for the column or datatype, NULL is entered. See also create table in the Reference Manual. • If the column has the IDENTITY property, a unique, sequential value is entered. • If NULL was not specified for the column when the table was created and no default exists, Adaptive Server rejects the row and displays an error message. Table 9-4 shows what you would see under these circumstances: Table 9-4: Columns with no values You can use sp_help to get a report on a specified table or default or on any other object listed in the system table sysobjects. To see the definition of a default, use sp_helptext. Changing a column’s value to NULL To set a column value to NULL, use the update statement: set column_name = {expression | null} [, column_name = {expression | null}]... For example, to find all rows in which the title_id is TC3218 and replace the advance with NULL: update titles set advance = null where title_id = "TC3218" Default Exists for Column or Datatype Column Defined NOT NULL Column Defined to Allow NULL Column Is IDENTITY Yes The default The default Next sequential value No Error message NULL Next sequential valueAdding new data 330 Adaptive Server Enterprise Adaptive Server-generated values for IDENTITY columns When you insert a row into a table with an IDENTITY column, Adaptive Server automatically generates the column value. Do not include the name of the IDENTITY column in the column list or its value in the values list. This insert statement adds a new row to the sales_daily table. Notice that the column list does not include the IDENTITY column, row_id: insert sales_daily (stor_id) values ("7896") The following statement shows the row that was added to sales_daily. Adaptive Server automatically generated the next sequential value, 2, for row_id: select * from sales_daily where stor_id = "7896" sale_id stor_id ------- ------- 1 7896 (1 row affected) Explicitly inserting data into an IDENTITY column At times, you may want to insert a specific value into an IDENTITY column, rather than accept a server-generated value. For example, you may want the first row inserted into the table to have an IDENTITY value of 101, rather than 1. Or you may need to reinsert a row that was deleted by mistake. The table owner can explicitly insert a value into an IDENTITY column. The Database Owner and System Administrator can explicitly insert a value into an IDENTITY column if they have been granted explicit permission by the table owner or if they are acting as the table owner through the setuser command. Before inserting the data, set the identity_insert option on for the table. You can set identity_insert on for only one table at a time in a database within a session. This example specifies a “seed” value of 101 for the IDENTITY column: set identity_insert sales_daily on insert sales_daily (syb_identity, stor_id) values (101, "1349")CHAPTER 9 Adding, Changing, and Deleting Data Transact-SQL User’s Guide 331 The insert statement lists each column, including the IDENTITY column, for which a value is specified. When the identity_insert option is set to on, each insert statement for the table must specify an explicit column list. The values list must specify an IDENTITY column value, since IDENTITY columns do not allow null values. After you set identity_insert off, you can insert IDENTITY column values automatically, without specifying the IDENTITY column, as before. Subsequent insertions use IDENTITY values based on the value explicitly specified after you set identity_insert on. For example, if you specify 101 for the IDENTITY column, subsequent insertions would be 102, 103, and so on. Note Adaptive Server does not enforce the uniqueness of the inserted value. You can specify any positive integer within the range allowed by the column’s declared precision. To ensure that only unique column values are accepted, create a unique index on the IDENTITY column before inserting any rows. Retrieving IDENTITY column values with @@identity Use the @@identity global variable to retrieve the last value inserted into an IDENTITY column. The value of @@identity changes each time an insert, select into, or bcp statement attempts to insert a row into a table. @@identity does not revert to its previous value if the insert, select into, or bcp statement fails or if the transaction that contains it is rolled back. If the statement affects a table without an IDENTITY column, @@identity is set to 0. • If the statement inserts multiple rows, @@identity reflects the last value inserted into the IDENTITY column. The value for @@identity within a stored procedure or trigger does not affect the value outside the stored procedure or trigger. For example: select @@identity --------------------------------------- 101 create procedure reset_id as set identity_insert sales_daily on insert into sales_daily (syb_identity, stor_id) values (102, "1349") select @@identity select @@identity execute reset_id --------------------------------------- 102Adding new data 332 Adaptive Server Enterprise select @@identity --------------------------------------- 101 Reserving a block of IDENTITY column values The identity grab size configuration parameter allows each Adaptive Server process to reserve a block of IDENTITY column values for inserts into tables that have an IDENTITY column. This configuration parameter reduces the number of times an Adaptive Server engine must hold an internal synchronization structure when inserting implicit identity values. For example, to set the number of reserved values to 20: sp_configure "identity grab size", 20 When a user performs an insert into a table containing an IDENTITY column, Adaptive Server reserves a block of 20 IDENTITY column values for that user. Therefore, during the current session, the next 20 rows the user inserts into the table will have sequential IDENTITY column values. If a second user inserts rows into the same table while the first user is performing inserts, Adaptive Server will reserve the next block of 20 IDENTITY column values for the second user. For example, suppose the following table containing an IDENTITY column has been created and the identity grab size is set to 10: create table my_titles (title_id numeric(5,0) identity, title varchar(30) not null) User 1 inserts these rows into the my_titles table: insert my_titles (title) values ("The Trauma of the Inner Child") insert my_titles (title) values ("A Farewell to Angst") insert my_titles (title) values ("Life Without Anger") Adaptive Server allows user 1 a block of 10 sequential IDENTITY values, for example, title_id numbers 1–10. While user 1 is inserting rows to my_titles, user 2 begins inserting rows into my_titles. Adaptive Server grants user 2 the next available block of reserved IDENTITY values, that is, values 11–20. CHAPTER 9 Adding, Changing, and Deleting Data Transact-SQL User’s Guide 333 If user 1 enters only three titles and then logs off Adaptive Server, the remaining seven reserved IDENTITY values are lost. The result is a gap in the table’s IDENTITY values. Avoid setting the identity grab size too high, because this can cause gaps in the IDENTITY column numbering. Reaching the IDENTITY column’s maximum value The maximum value that you can insert into an IDENTITY column is 10 precision - 1. If you do not specify a precision for the IDENTITY column, Adaptive Server uses the default precision (18 digits) for numeric columns. Once an IDENTITY column reaches its maximum value, insert statements return an error that aborts the current transaction. When this happens, use one of the following methods to remedy the problem. Modify the IDENTITY column’s maximum value You can alter the maximum value of any IDENTITY column with a modify operation in the alter table command. alter table my_titles modify title_id, numeric (10,0) This operation performs a data copy on a table and rebuilds all the table indexes. Create a new table with a larger precision If the table contains IDENTITY columns that are used for referential integrity, you need to retain the current numbers for the IDENTITY column values. 1 Use create table to create a new table that is identical to the old one except with a larger precision value for the IDENTITY column. 2 Use insert into to copy the data from the old table into to the new one. Renumber the table’s IDENTITY columns with bcp If the table does not contain IDENTITY columns used for referential integrity, and if there are gaps in the numbering sequence, you can renumber the IDENTITY column to eliminate gaps, which allows more room for insertions. To sequentially renumber IDENTITY column values and remove the gaps, use the bcp utility: 1 From the operating system command line, use bcp to copy out the data. For example:Adding new data 334 Adaptive Server Enterprise bcp pubs2..mytitles out my_titles_file -N -c The -N instructs bcp not to copy the IDENTITY column values from the table to the host file. The -c instructs bcp to use character mode. 2 In Adaptive Server, create a new table that is identical to the old table. 3 From the operating system command line, use bcp to copy the data into the new table: bcp pubs2..mynewtitles in my_titles_file -N -c The -N instructs bcp to have Adaptive Server assign the IDENTITY column values when loading data from the host file. The -c instructs bcp to use character mode. 4 In Adaptive Server, drop the old table, and use sp_rename to change the new table name to the old table name. If the IDENTITY column is a primary key for joins, you may need to update the foreign keys in other tables. By default, when you bulk copy data into a table with an IDENTITY column, bcp assigns each row a temporary IDENTITY column value of 0. As it inserts each row into the table, the server assigns it a unique, sequential IDENTITY column value, beginning with the next available value. To enter an explicit IDENTITY column value for each row, specify the -E (UNIX) or /identity (OpenVMS) flag. Refer to the Utility Guide for your platform for more information on bcp options that affect IDENTITY columns. Adding new rows with select To pull values into a table from one or more other tables, use a select clause in the insert statement. The select clause can insert values into some or all of the columns in a row. Inserting values for only some columns can come in handy when you want to take some values from an existing table. Then, you can use update to add the values for the other columns. Before inserting values for some, but not all, columns in a table, make sure that a default exists or that NULL has been specified for the columns for which you are not inserting values. Otherwise, Adaptive Server returns an error message. CHAPTER 9 Adding, Changing, and Deleting Data Transact-SQL User’s Guide 335 When you insert rows from one table into another, the two tables must have compatible structures—that is, the matching columns must be either the same datatypes or datatypes between which Adaptive Server automatically converts. Note You cannot insert data from a table that allows null values into a table that does not, if any of the data being inserted is null. If the columns are in the same order in their create table statements, you do not need to specify column names in either table. Suppose you have a table named newauthors that contains some rows of author information in the same format as in authors. To add to authors all the rows in newauthors: insert authors select * from newauthors To insert rows into a table based on data in another table, the columns in the two tables do not have to be listed in the same sequence in their respective create table statements. You can use either the insert or the select statement to order the columns so that they match. For example, suppose the create table statement for the authors table contained the columns au_id, au_fname, au_lname, and address, in that order, and newauthors contained au_id, address, au_lname, and au_fname. You would have to make the column sequence match in the insert statement. You could do this in either of two ways: insert authors (au_id, address, au_lname, au_fname) select * from newauthors or insert authors select au_id, au_fname, au_lname, address from newauthors If the column sequence in the two tables fails to match, Adaptive Server either cannot complete the insert operation, or completes it incorrectly, putting data in the wrong column. For example, you might get address data in the au_lname column. Adding new data 336 Adaptive Server Enterprise Computed columns You can use computed columns in a select statement inside an insert statement. For example, imagine that a table named tmp contains some new rows for the titles table, which contains some out-of-date data—the price figures need to be doubled. A statement to increase the prices and insert the tmp rows into titles looks like: insert titles select title_id, title, type, pub_id, price*2, advance, total_sales, notes, pubdate, contract from tmp When you perform computations on a column, you cannot use the select * syntax. Each column must be named individually in the select list. Inserting data into some columns You can use the select statement to add data to some, but not all, columns in a row just as you do with the values clause. Simply specify the columns to which you want to add data in the insert clause. For example, some authors in the authors table do not have titles and, therefore, do not have entries in the titleauthor table. To pull their au_id numbers out of the authors table and insert them into the titleauthor table as placeholders, try this statement: insert titleauthor (au_id) select au_id from authors where au_id not in (select au_id from titleauthor) This statement is not legal, because a value is required for the title_id column. Null values are not permitted and no default is specified. You can enter the dummy value “xx1111” for titles_id by using a constant, as follows: insert titleauthor (au_id, title_id) select au_id, "xx1111" from authors where au_id not in (select au_id from titleauthor) The titleauthor table now contains four new rows with entries for the au_id column, dummy entries for the title_id column, and null values for the other two columns.CHAPTER 9 Adding, Changing, and Deleting Data Transact-SQL User’s Guide 337 Inserting data from the same table You can insert data into a table based on other data in the same table. Essentially, this means copying all or part of a row. For example, you can insert a new row in the publishers table that is based on the values in an existing row in the same table. Make sure you follow the rule on the pub_id column: insert publishers select "9999", "test", city, state from publishers where pub_name = "New Age Books" (1 row affected) select * from publishers pub_id pub_name city state ------- --------------------- ------- ------ 0736 New Age Books Boston MA 0877 Binnet & Hardley Washington DC 1389 Algodata Infosystems Berkeley CA 9999 test Boston MA (4 rows affected) The example inserts the two constants (“9999” and “test”) and the values from the city and state columns in the row that satisfied the query. Changing existing data Use the update command to change single rows, groups of rows, or all rows in a table. As in all data modification statements, you can change the data in only one table at a time. update specifies the row or rows you want changed and the new data. The new data can be a constant or an expression that you specify or data pulled from other tables. If an update statement violates an integrity constraint, the update does not take place and an error message is generated. The update is canceled, for example, if it affects the table’s IDENTITY column, or if one of the values being added is the wrong datatype, or if it violates a rule that has been defined for one of the columns or datatypes involved.Changing existing data 338 Adaptive Server Enterprise Adaptive Server does not prevent you from issuing an update command that updates a single row more than once. However, because of the way that update is processed, updates from a single statement do not accumulate. That is, if an update statement modifies the same row twice, the second update is not based on the new values from the first update but on the original values. The results are unpredictable, since they depend on the order of processing. See Chapter 10, “Views: Limiting Access to Data,” for restrictions on updating views. Note The update command is logged. If you are changing large blocks of text or image data, try using the writetext command, which is not logged. Also, you are limited to approximately 125K per update statement. See the discussion of writetext in “Changing text and image data” on page 342. update syntax A simplified version of the update syntax for updating specified rows with an expression is: update table_name set column_name = expression where search_conditions For example, if Reginald Blotchet-Halls decides to change his name, here is how to change his row in the authors table: update authors set au_lname = "Health", au_fname = "Goodbody" where au_lname = "Blotchet-Halls" This statement updates a table based on data from another table: update table_name set column_name = expression from table_name where search_conditions You can set variables in an update statement with: update table_name set variable_name = expression where search_conditions The full syntax for update is: CHAPTER 9 Adding, Changing, and Deleting Data Transact-SQL User’s Guide 339 update [[database.]owner.]{table_name | view_name} set [[[database.]owner.]{table_name. | view_name.}] column_name1 = {expression1 | null | (select_statement)} | variable_name1 = {expression1 | null | (select_statement)} [, column_name2 = {expression2 | null | (select_statement)}]... | variable_name2 = {expression1 | null | (select_statement)} [from [[database.]owner.] {table_name | view_name} [, [[database.]owner.] {table_name | view_name}]]... [where search_conditions] Using the set clause with update The set clause specifies the columns and the changed values. The where clause determines which row or rows are to be updated. If you do not have a where clause, the specified columns of all the rows are updated with the values given in the set clause. Note Before trying the examples in this section, make sure you know how to reinstall the pubs2 database. See the installation and configuration guide for your platform for instructions on installing the pubs2 database. For example, if all the publishing houses in the publishers table move their head offices to Atlanta, Georgia, this is how you update the table: update publishers set city = "Atlanta", state = "GA" In the same way, you can change the names of all the publishers to NULL with: update publishers set pub_name = null You can also use computed column values in an update. To double all the prices in the titles table, use: update titles set price = price * 2 Since there is no where clause, the change in prices is applied to every row in the table. Changing existing data 340 Adaptive Server Enterprise Assigning variables in the set clause You can assign variables in the set clause of an update statement, in the same way you can assign them in a select statement. Using variables with update reduces lock contention and CPU consumption that can occur when extra select statements are used in conjunction with update. This example uses a declared variable to update the titles table: declare @price money select @price = 0 update titles set total_sales = total_sales + 1, @price = price where title_id = "BU1032" select @price, total_sales from titles where title_id = "BU1032" total_sales ------------------------ ----------- 19.99 4096 (1 row affected) For details on assigning variables in an update statement, see the Reference Manual. For more information on declared variables, see “Local variables” on page 478. Using the where clause with update The where clause specifies which rows are to be updated. For example, in the unlikely event that Northern California is renamed Pacifica (abbreviated PC) and the people of Oakland vote to change the name of their city to Big Bad Bay City, here is how you can update the authors table for all former Oakland residents whose addresses are now out of date: update authors set state = "PC", city = "Big Bad Bay City" where state = "CA" and city = "Oakland" You need to write another statement to change the name of the state for residents of other cities in Northern California. CHAPTER 9 Adding, Changing, and Deleting Data Transact-SQL User’s Guide 341 Using the from clause with update Use the from clause to pull data from one or more tables into the table you are updating. For example, earlier in this chapter, an example was given for inserting some new rows into the titleauthor table for authors without titles, filling in the au_id column, and using dummy or null values for the other columns. When one of these authors, Dirk Stringer, writes a book, The Psychology of Computer Cooking , a title identification number is assigned to his book in the titles table. You can modify his row in the titleauthor table by adding a title identification number for him: update titleauthor set title_id = titles.title_id from titleauthor, titles, authors where titles.title = "The Psychology of Computer Cooking" and authors.au_id = titleauthor.au_id and au_lname = "Stringer" Note that an update without the au_id join changes all the title_ids in the titleauthor table so that they are the same as The Psychology of Computer Cooking ’s identification number. If two tables are identical in structure except that one has NULL fields and some null values and the other has NOT NULL fields, it is impossible to insert the data from the NULL table into the NOT NULL table with a select. In other words, a field that does not allow NULL cannot be updated by selecting from a field that does, if any of the data is NULL. As an alternative to the from clause in the update statement, you can use a subquery, which is ANSI-compliant. Updates with joins The following example joins columns from the titles and publishers tables, doubling the price of all books published in California: update titles set price = price * 2 from titles, publishers where titles.pub_id = publishers.pub_id and publishers.state = "CA" Although a join can usually be done with up to 16 tables, if a join is part of an update or delete statement, the query can only refer to 15 tables.Changing text and image data 342 Adaptive Server Enterprise Updating IDENTITY columns You can use the syb_identity keyword, qualified by the table name, where necessary, to update an IDENTITY column. For example, this update statement finds the row in which the IDENTITY column equals 1 and changes the name of the store to “Barney’s”: update stores_cal set stor_name = "Barney’s" where syb_identity = 1 Changing text and image data Use writetext to change text or image values when you do not want to store long text values in the database transaction log. Do not use the update command, which can also be used for text or image columns, because update commands are always logged. In its default mode, writetext commands are not logged. Note To use writetext in its default, non-logged state, a System Administrator must use sp_dboption to set select into/bulkcopy/pllsort on. This permits the insertion of non-logged data. After using writetext, it is necessary to dump the database. You cannot use dump transaction after making unlogged changes to the database. The writetext command completely overwrites any data in the column it affects. The column must already contain a valid text pointer. You can use the textvalid() function to check for a valid pointer: select textvalid("blurbs.copy", textptr(copy)) from blurbs There are two ways to create a text pointer: • insert actual data into the text or image column • update the column with data or a NULL CHAPTER 9 Adding, Changing, and Deleting Data Transact-SQL User’s Guide 343 An “initialized” text column uses 2K of storage, even to store a couple of words. Adaptive Server saves space by not initializing text columns when explicit or implicit null values are placed in text columns with insert. The following code fragment inserts a value with a null text pointer, checks for the existence of a text pointer, and then updates the blurbs table. Explanatory comments are embedded in the text: /* Insert a value with a text pointer. This could ** be done in a separate batch session. */ insert blurbs (au_id) values ("267-41-2394") /* Check for a valid pointer in an existing row. ** Use textvalid in a conditional clause; if no ** valid text pointer exists, update ’copy’ to null ** to initialize the pointer. */ if (select textvalid("blurbs.copy", textptr(copy)) from blurbs where au_id = "267-41-2394") = 0 begin update blurbs set copy = NULL where au_id = "267-41-2394" end /* ** use writetext to insert the text into the ** column. The next statements put the text ** into the local variable @val, then writetext ** places the new text string into the row ** pointed to by @val. */ declare @val varbinary(16) select @val = textptr(copy) from blurbs where au_id = "267-41-2394" writetext blurbs.copy @val "This book is a must for true data junkies." For more information on batch files and the control-of-flow language used in this example, see Chapter 14, “Using Batches and Control-of-Flow Language.” Deleting data delete works for both single-row and multiple-row operations. Deleting data 344 Adaptive Server Enterprise A simplified version of delete syntax is: delete table_name where column_name = expression Here is the complete syntax statement, which shows that you can remove rows either on the basis of specified expressions or based on data from other tables: delete [from] [[database.]owner.]{view_name | table_name} [where search_conditions] delete [[database.]owner.] {table_name | view_name} [from [[database.]owner.]{view_name | table_name [(index {index_name | table_name } [prefetch size ] [ lru | mru])]} [, [[database.]owner.] {view_name | table_name (index {index_name | table_name } [prefetch size ] [lru | mru])]}]...] [where search_conditions] delete [from] [[database.]owner.] {table_name | view_name} where current of cursor_name The where clause specifies which rows are to be removed. When no where clause is given in the delete statement, all rows in the table are removed. Using the from clause with delete The optional from immediately after the delete keyword is included for compatibility with other versions of SQL. The from clause in the second position of a delete statement is a special Transact-SQL feature that allows you to select data from a table or tables and delete corresponding data from the firstnamed table. The rows you select in the from clause specify the conditions for the delete. Suppose that a complex corporate deal results in the acquisition of all the Big Bad Bay City (formerly Oakland) authors and their books by another publisher. You need to remove all these books from the titles table right away, but you do not know their titles or identification numbers. The only information you have is the author’s names and addresses. CHAPTER 9 Adding, Changing, and Deleting Data Transact-SQL User’s Guide 345 You can delete the rows in titles by finding the author identification numbers for the rows that have Big Bad Bay City as the town in the authors table and using these numbers to find the title identification numbers of the books in the titleauthor table. In other words, a three-way join is required to find the rows to delete in the titles table. The three tables are all included in the from clause of the delete statement. However, only the rows in the titles table that fulfill the conditions of the where clause are deleted. You would have to use separate delete statements to remove relevant rows in tables other than titles. Here is the statement you need: delete titles from authors, titles, titleauthor where titles.title_id = titleauthor.title_id and authors.au_id = titleauthor.au_id and city = "Big Bad Bay City" The deltitle trigger in the pubs2 database prevents you from actually performing this deletion, because it does not allow you to delete any titles that have sales recorded in the sales table. Deleting from IDENTITY columns You can use the syb_identity keyword in a delete statement on tables containing an IDENTITY column. For example, this statement removes the row for which row_id equals 1: delete sales_monthly where syb_identity = 1 After you delete IDENTITY column rows, you may want to eliminate gaps in the table’s IDENTITY column numbering sequence. See “Renumber the table’s IDENTITY columns with bcp” on page 333.Deleting all rows from a table 346 Adaptive Server Enterprise Deleting all rows from a table Use truncate table to delete all rows in a table. It is almost always faster than a delete statement with no conditions, because the delete logs each change, while truncate table just logs the deallocation of entire data pages. truncate table immediately frees all the space that the table’s data and indexes had occupied. The freed space can then be used by any object. The distribution pages for all indexes are also deallocated. Run update statistics after adding new rows to the table. As with delete, a table emptied with truncate table remains in the database, along with its indexes and other associated objects, unless you enter a drop table command. You cannot use truncate table if another table has rows that reference it through a referential integrity constraint. Delete the rows from the foreign table, or truncate the foreign table and then truncate the primary table. See “General rules for creating referential integrity constraints” on page 270. truncate table syntax The syntax of truncate table is: truncate table [[database.]owner.]table_name For example, to remove all the data in sales, type: truncate table sales Permission to use truncate table, like drop table, defaults to the table owner and cannot be transferred. A truncate table command is not caught by a delete trigger. See Chapter 17, “Triggers: Enforcing Referential Integrity.”Transact-SQL User’s Guide 347 C H A P T E R 1 0 Views: Limiting Access to Data A view is a named select statement that is stored in a database as an object. It allows you to view a subset of rows or columns in one or more tables. You use the view by invoking its name in other Transact-SQL statements. You can use views to focus, simplify, and customize each user’s perception of the tables in a particular database. Views also provide a security mechanism by allowing users access only to the data they require. This chapter discusses: How views work A view is an alternative way of looking at the data in one or more tables. For example, suppose you are working on a project that is specific to the state of Utah. You can create a view that lists only the authors who live in Utah: create view authors_ut as select * from authors where state = "UT" To display the authors_ut view, enter: select * from authors_ut When the authors who live in Utah are added to or removed from the authors table, the authors_ut view reflects the updated authors table. Topic Page How views work 347 Creating views 352 Retrieving data through views 360 Modifying data through views 364 Dropping views 368 Using views as security mechanisms 369 Getting information about views 369How views work 348 Adaptive Server Enterprise A view is derived from one or more real tables whose data is physically stored in the database. The tables from which a view is derived are called its base tables or underlying tables. A view can also be derived from another view. The definition of a view, in terms of the base tables from which it is derived, is stored in the database. No separate copies of data are associated with this stored definition. The data that you view is stored in the underlying tables. A view looks exactly like any other database table. You can display it and operate on it almost exactly as you can any other table. There are no restrictions at all on querying through views and fewer than usual on modifying them. The exceptions are explained later in this chapter. When you modify the data in a view, you are actually changing the data in the underlying base tables. Conversely, changes to data in the underlying base tables are automatically reflected in the views that are derived from them. Advantages of views You can use views to focus, simplify, and customize each user’s perception of the database; they also provide an easy-to-use security measure. Views can also be helpful when changes have been made to the structure of a database, but users prefer to work with the structure of the database they are accustomed to. You can use views to: • Focus on the data that interests them and on the tasks for which they are responsible. Data that is not of interest to a user can be left out of the view. • Define frequently used joins, projections, and selections as views so that users do not have to specify all the conditions and qualifications each time an operation is performed on that data. • Display different data for different users, even when they are using the same data at the same time. This advantage is particularly important when users of many different interests and skill levels share the same database. Security Through a view, users can query and modify only the data they can see. The rest of the database is neither visible nor accessible. CHAPTER 10 Views: Limiting Access to Data Transact-SQL User’s Guide 349 With the grant and revoke commands, each user’s access to the database can be restricted to specified database objects—including views. If a view and all the tables and other views from which it is derived are owned by the same user, that user can grant permission to others to use the view while denying permission to use its underlying tables and views. This is a simple but effective security mechanism. See the System Administration Guide for details on the grant and revoke commands. By defining different views and selectively granting permissions on them, users can be restricted to different subsets of data. For example: • Access can be restricted to a subset of the rows of a base table, that is, a value-dependent subset. For example, you might define a view that contains only the rows for business and psychology books, in order to keep information about other types of books hidden from some users. • Access can be restricted to a subset of the columns of a base table, that is, a value-independent subset. For example, you might define a view that contains all the rows of the titles table, except the royalty and advance columns. • Access can be restricted to a row-and-column subset of a base table. • Access can be restricted to the rows that qualify for a join of more than one base table. For example, you might define a view that joins the titles, authors, and titleauthor to display the names of the authors and the books they have written. This view would hide personal data about authors and financial information about the books. • Access can be restricted to a statistical summary of data in a base table. For example, through the view category_price a user can access only the average price of each type of book. • Access can be restricted to a subset of another view or a combination of views and base tables. For example, through the view hiprice_computer a user can access the title and price of computer books that meet the qualifications in the view definition of hiprice. To create a view, a user must be granted create view permission by the Database Owner, and must have appropriate permissions on any tables or views referenced in the view definition. If a view references objects in different databases, users of the view must be valid users or guests in each of the databases.How views work 350 Adaptive Server Enterprise If you own an object on which other users have created views, you must be aware of who can see what data through what views. For example: the Database Owner has granted “harold” create view permission, and “maude” has granted “harold” permission to select from a table she owns. Given these permissions, “harold” can create a view that selects all columns and rows from the table owned by “maude.” If “maude” revokes permission for “harold” to select from her table, he can still look at her data through the view he has created. Logical data independence Views can shield users from changes in the structure of the real tables if such changes become necessary. For example, suppose you restructure the database by using select into to split the titles table into these two new base tables and then dropping the titles table: titletext (title_id, title, type, notes) titlenumbers (title_id, pub_id, price, advance, royalty, total_sales, pub_date) The old titles table can be “regenerated” by joining on the title_id columns of the two new tables. You can create a view that is a join of the two new tables. You can even name it titles. Any query or stored procedure that previously referred to the base table titles now refers to the view titles. As far as the users are concerned, select operations work exactly as before. Users who retrieve only from the new view need not even know that the restructuring has occurred. Unfortunately, views provide only partial logical independence. Some data modification statements on the new titles are not allowed because of certain restrictions. View examples The first example is a view derived from the titles table. Suppose you are interested only in books priced higher than $15 and for which an advance of more than $5000 was paid. This straightforward select statement finds the rows that qualify: select * from titles where price > $15 CHAPTER 10 Views: Limiting Access to Data Transact-SQL User’s Guide 351 and advance > $5000 Now, suppose you have a lot of retrieval and update operations to do on this collection of data. You could, of course, combine the conditions shown in the previous query with any command that you issue. However, for convenience, you can create a view that displays only the records of interest: create view hiprice as select * from titles where price > $15 and advance > $5000 When Adaptive Server receives this command, it does not actually execute the select statement that follows the keyword as. Instead, it stores the select statement, which is the definition of the view hiprice, in the system table syscomments. Entries are also made in sysobjects and in syscolumns for each column included in the view. Now, when you display or operate on hiprice, Adaptive Server combines your statement with the stored definition of hiprice. For example, you can change all the prices in hiprice just as you can change any other table: update hiprice set price = price * 2 Adaptive Server finds the view definition in the system tables and converts the update command into the statement: update titles set price = price * 2 where price > $15 and advance > $5000 In other words, Adaptive Server knows from the view definition that the data to be updated is in titles. It also knows that it should increase the prices only in the rows that meet the conditions on the price and advance columns given in the view definition and those in the update statement. Having issued the update to hiprice, you can see its effect either in the view or in the titles table. Conversely, if you had created the view and then issued the second update statement, which operates directly on the base table, the changed prices would also be visible through the view. Creating views 352 Adaptive Server Enterprise Updating a view’s underlying table in such a way that different rows qualify for the view affects the view. For example, suppose you increase the price of the book You Can Combat Computer Stress to $25.95. Since this book now meets the qualifying conditions in the view definition statement, it is considered part of the view. However, if you alter the structure of a view’s underlying table by adding columns, the new columns will not appear in a view that is defined with a select * clause unless the view is dropped and redefined. This is because the asterisk in the original view definition considers only the original columns. Creating views View names must be unique for each user among the already existing tables and views. If you have set quoted_identifier on, you can use a delimited identifier for the view. Otherwise, the view name must follow the rules for identifiers given in “Identifiers” on page 7. You can build views on other views and procedures that reference views. You can define primary, foreign, and common keys on views. However, you cannot associate rules, defaults, or triggers with views or build indexes on them. You cannot create temporary views or views on temporary tables. create view syntax Here is the full syntax for create view: create view [owner .]view_name [(column_name [, column_name ]...)] as select [distinct] select_statement [with check option] As illustrated in the create view example in “View examples” on page 350, you need not specify any column names in the create clause of a view definition statement. Adaptive Server gives the columns of the view the same names and datatypes as the columns referred to in the select list of the select statement. The select list can be designated by the asterisk (*), as in the example, or it can be a full or partial list of the column names in the base tables. CHAPTER 10 Views: Limiting Access to Data Transact-SQL User’s Guide 353 To build views that do not contain duplicate rows, use the distinct keyword of the select statement to ensure that each row in the view is unique. However, you cannot update distinct views. You can always specify column names. However, if any of the following are true, you must specify column names in the create clause for every column in the view: • One or more of the view’s columns are derived from an arithmetic expression, an aggregate, a built-in function, or a constant. • Two or more of the view’s columns would otherwise have the same name. This usually happens because the view definition includes a join, and the columns being joined have the same name. • You want to give a column in the view a different name than the column from which it is derived. You can also rename columns in the select statement. Whether or not you rename a view column, it inherits the datatype of the column from which it is derived. Here is a view definition statement that makes the name of a column in the view different from its name in the underlying table: create view pub_view1 (Publisher, City, State) as select pub_name, city, state from publishers Here is an alternate method of creating the same view but renaming the columns in the select statement: create view pub_view2 as select Publisher = pub_name, City = city, State = state from publishers The examples of view definition statements in the next section illustrate the rest of the rules for including column names in the create clause. Note Local variables cannot be used in view definitions.Creating views 354 Adaptive Server Enterprise Using the select statement with create view The select statement in the create view statement defines the view. You must have permission to select from any objects referenced in the select statement of a view you are creating. You can create a view using more than one table and other views by using a select statement of any complexity. There are a few restrictions on the select statements in a view definition: • You cannot include order by or compute clauses. • You cannot include the into keyword. • You cannot reference a temporary table. View definition with projection To create a view with all the rows of the titles table, but with only a subset of its columns, enter: create view titles_view as select title, type, price, pubdate from titles Note that no column names are included in the create view clause. The view titles_view inherits the column names given in the select list. View definition with a computed column Here is a view definition statement that creates a view with a computed column generated from the columns price, royalty, and total_sales: create view accounts (title, advance, amt_due) as select titles.title_id, advance, (price * royalty /100) * total_sales from titles, roysched where price > $15 and advance > $5000 and titles.title_id = roysched.title_id and total_sales between lorange and hirange There is no name that can be inherited by the column computed by multiplying together price, royalty, and total_sales, so you must include the list of columns in the create clause. The computed column is named amt_due. It must be listed in the same position in the create clause as the expression from which it is computed is listed in the select clause. CHAPTER 10 Views: Limiting Access to Data Transact-SQL User’s Guide 355 View definition with an aggregate or built-in function A view definition that includes an aggregate or built-in function must include column names in the create clause. For example: create view categories1 (category, average_price) as select type, avg(price) from titles group by type If you create a view for security reasons, be careful when using aggregate functions and the group by clause. The Transact-SQL extension that does not restrict the columns you can include in the select with group by may also cause the view to return more information than required. For example: create view categories2 (category, average_price) as select type, avg(price) from titles where type = "business" In the above case, you may have wanted the view to restrict its results to “business” categories, but the results have information about other categories. For more information about group by and this group by Transact-SQL extension, see “Organizing query results into groups: the group by clause” on page 85. View definition with a join You can create a view derived from more than one base table. Here is an example of a view derived from both the authors and the publishers tables. The view contains the names and cities of the authors that live in the same city as a publisher, along with each publisher’s name and city. create view cities (authorname, acity, publishername, pcity) as select au_lname, authors.city, pub_name, publishers.city from authors, publishers where authors.city = publishers.cityCreating views 356 Adaptive Server Enterprise Views used with outer joins If you define a view with an outer join, and then query the view with a qualification on a column from the inner table of the outer join, the query behaves as though the qualification were part of the WHERE clause of the view, not part of the ON clause of the outer join in the view. Thus the qualification operates only on rows AFTER the outer join is complete. For example, the qualification operates on NULL extended rows if the outer join condition is met, and eliminates rows accordingly. The following rules determine what types of updates you can make to columns through join views: • delete statements are not allowed on join views. • insert statements are not allowed on join views created with check option. • update statements are allowed on join views with check option. The update fails if any of the affected columns appears in the where clause, in an expression that includes columns from more than one table. • If you insert or update a row through a join view, all affected columns must belong to the same base table. Views derived from other views You can define a view in terms of another view, as in this example: create view hiprice_computer as select title, price from hiprice where type = "popular_comp" distinct views You can ensure that the rows contained in a view are unique, as in this example: create view author_codes as select distinct au_id from titleauthor A row is a duplicate of another row if all of its column values match the same column values contained in another row. Two null values are considered to be identical.CHAPTER 10 Views: Limiting Access to Data Transact-SQL User’s Guide 357 Adaptive Server applies the distinct requirement to the view’s definition when it accesses the view for the first time, before it does any projecting or selecting. Views look and act like any database table. If you select a projection of the distinct view (that is, you select only some of the view’s columns, but all of its rows), you can get results that appear to be duplicates. However, each row in the view itself is still unique. For example, suppose that you create a distinct view, myview, with three columns, a, b, and c , that contains these values: When you enter this query: select a, b from myview the results look like this: a b --- --- 1 1 1 2 1 1 (3 rows affected) The first and third rows appear to be duplicates. However, the underlying view’s rows are still unique. Views that include IDENTITY columns You can define a view that includes an IDENTITY column by listing the column name, or the syb_identity keyword, in the view’s select statement. For example: create view sales_view as select syb_identity, stor_id from sales_daily However, you cannot add a new IDENTITY column to a view by using the identity_column_name = identity(precision) syntax. You can select the IDENTITY column from the view using the syb_identity keyword, unless the view: • Selects the IDENTITY column more than once a b c 1 1 2 1 2 3 1 1 0Creating views 358 Adaptive Server Enterprise • Computes a new column from the IDENTITY column • Includes an aggregate function • Joins columns from multiple tables • Includes the IDENTITY column as part of an expression If any of these conditions is true, Adaptive Server does not recognize the column as an IDENTITY column with respect to the view. When you execute sp_help on the view, the column displays an “Identity” value of 0. In the following example, the row_id column is not recognized as an IDENTITY column with respect to the store_discounts view because store_discounts joins columns from two tables: create view store_discounts as select stor_name, discount from stores, new_discounts where stores.stor_id = new_discounts.stor_id When you define the view, the underlying column retains the IDENTITY property. When you update a row through the view, you cannot specify a new value for the IDENTITY column. When you insert a row through the view, Adaptive Server generates a new, sequential value for the IDENTITY column. Only the table owner, Database Owner, or System Administrator can explicitly insert a value into the IDENTITY column after setting identity_insert on for the column’s base table. After creating a view After you create a view, the source text describing the view is stored in the text column of the syscomments system table. Do not remove this information from syscomments. Instead, encrypt the text in syscomments by using sp_hidetext, which is described in the Reference Manual. For more information, see “Compiled objects” on page 4.CHAPTER 10 Views: Limiting Access to Data Transact-SQL User’s Guide 359 Validating a view’s selection criteria using with check option Normally, Adaptive Server does not check insert and update statements on views to determine whether the affected rows are within the scope of the view. A statement can insert a row into the underlying base table, but not into the view, or change an existing row so that it no longer meets the view’s selection criteria. When you create a view using the with check option clause, each insert and update through the view, is validated against the view’s selection criteria. All rows inserted or updated through the view must remain visible through the view, or the statement fails. Here is an example of a view, stores_ca, created using with check option. This view includes information about stores located in California, but excludes information about stores located in any other state. The view is created by selecting all rows from the stores table for which state has a value of “CA”: create view stores_ca as select * from stores where state = "CA" with check option When you try to insert a row through stores_ca, Adaptive Server verifies that the new row falls within the scope of the view. The following insert statement fails because the new row would have a state value of “NY”, rather than “CA”: insert stores_ca values ("7100", "Castle Books", "351 West 24 St.", "New York", "NY", "USA", "10011", "Net 30") When you try to update a row through stores_cal, Adaptive Server verifies that the update will not cause the row to disappear from the view. The following update statement fails because it would change the value of state from “CA” to “MA”. After the update, the row would no longer be visible through the view. update stores_ca set state = "CA" where stor_id = "7066" Views derived from other views When a view is created using with check option, all views derived from the “base” view must satisfy its check option. Each row inserted through the derived view must be visible through the base view. Each row updated through the derived view must remain visible through the base view.Retrieving data through views 360 Adaptive Server Enterprise Consider the view stores_cal30, which is derived from stores_cal. The new view includes information about stores in California with payment terms of “Net 30”: create view stores_cal30 as select * from stores_ca where payterms = "Net 30" Because stores_cal was created using with check option, all rows inserted or updated through stores_cal30 must be visible through stores_cal. Any row with a state value other than “CA” is rejected. Notice that stores_cal30 does not have a with check option clause of its own. This means that it is possible to insert or update a row with a payterms value other than “Net 30” through stores_cal30. The following update statement would be successful, even though the row would no longer be visible through stores_cal30: update stores_cal30 set payterms = "Net 60" where stor_id = "7067" Retrieving data through views When you retrieve data through a view, Adaptive Server checks to make sure that all the database objects referenced anywhere in the statement exist and that they are valid in the context of the statement. If the checks are successful, Adaptive Server combines the statement with the stored definition of the view and translates it into a query on the view’s underlying tables. This process is called view resolution. Consider the following view definition statement and a query against it: create view hiprice as select * from titles where price > $15 and advance > $5000 select title, type from hiprice where type = "popular_comp" Internally, Adaptive Server combines the query of hiprice with its definition, converting the query to: CHAPTER 10 Views: Limiting Access to Data Transact-SQL User’s Guide 361 select title, type from titles where price > $15 and advance > $5000 and type = "popular_comp" In general, you can query any view in any way just as if it were a real table. You can use joins, group by clauses, subqueries, and other query techniques on views, in any combination. Note, however, that if the view is defined with an outer join or aggregate function, you may get unexpected results when you query the view. See “Views derived from other views” on page 356. Note You can use select on text and image columns in views. However, you cannot use readtext and writetext in views. View resolution When you define a view, Adaptive Server verifies that all the tables or views listed in the from clause exist. Similar checks are performed when you query through the view. Between the time a view is defined and the time it is used in a statement, things can change. For example, one or more of the tables or views listed in the from clause of the view definition may have been dropped. Or one or more of the columns listed in the select clause of the view definition may have been renamed. To fully resolve a view, Adaptive Server verifies that: • All the tables, views, and columns from which the view was derived still exist. • The datatype of each column on which a view column depends has not been changed to an incompatible type. • If the statement is an update, insert, or delete, it does not violate the restrictions on modifying views. These are discussed under “Modifying data through views” on page 364. If any of these checks fails, Adaptive Server issues an error message. Retrieving data through views 362 Adaptive Server Enterprise Redefining views Adaptive Server allows you to redefine a view without forcing you to redefine other views that depend on it, unless the redefinition makes it impossible for Adaptive Server to translate the dependent view. For example, the authors table and three possible views are shown below. Each succeeding view is defined using the view that preceded it: view2 is created from view1, and view3 is created from view2. In this way, view2 depends on view1 and view3 depends on both the preceding views. Each view name is followed by the select statement used to create it. view1: create view view1 as select au_lname, phone from authors where postalcode like "94%" view2: create view view2 as select au_lname, phone from view1 where au_lname like "[M-Z]%" view3: create view view3 as select au_lname, phone from view2 where au_lname = "MacFeather" The authors table on which these views are based consists of these columns: au_id, au_lname, au_fname, phone, address, city, state, and postalcode. You can drop view2 and replace it with another view, also named view2, that contains slightly different selection criteria, such as: create view view2 as select au_lname, phone from view3 where au_lname like "[M-P]" view3, which depends on view2, is still valid and does not need to be redefined. When you use a query that references either view2 or view3, view resolution takes place as usual. CHAPTER 10 Views: Limiting Access to Data Transact-SQL User’s Guide 363 If you redefine view2 so that view3 cannot be derived from it, view3 becomes invalid. For example, if another new version of view2 contains a single column, au_lname, rather than the two columns that view3 expects, view3 can no longer be used because it cannot derive the phone column from the object on which it depends. However, view3 still exists and you can use it again by dropping view2 and recreating view2 with both the au_lname and the phone columns. In short, you can change the definition of an intermediate view without affecting dependent views as long as the select list of the dependent views remains valid. If this rule is violated, a query that references the invalid view produces an error message. Renaming views You can rename a view using sp_rename: sp_rename objname , newname For example, to rename titleview to bookview, enter: sp_rename titleview, bookview Follow these conventions when renaming views: • Make sure the new name follows the rules used for identifiers discussed under “Identifiers” on page 7. • You can change the name only of views that you own. The Database Owner can change the name of any user’s view. • Make sure the view is in the current database. Altering or dropping underlying objects You can change the name of a view’s underlying objects. For example, if a view references a table entitled new_sales, and you rename that table to old_sales, the view will work on the renamed table. However, if a table referenced by a view has been dropped, and someone tries to use the view, Adaptive Server produces an error message. If a new table or view is created to replace the one that was dropped, the view again becomes usable. Modifying data through views 364 Adaptive Server Enterprise If you define a view with a select * clause, and then alter the structure of its underlying tables by adding columns, the new columns do not appear. This is because the asterisk shorthand is interpreted and expanded when the view is first created. To see the new columns, drop the view and re-create it. Modifying data through views Although Adaptive Server places no restrictions on retrieving data through views, and although Transact-SQL places fewer restrictions on modifying data through views than other versions of SQL, the following rules apply to various data modification operations: • update, insert, or delete operations that refer to a computed column or a built-in function in a view are not allowed. • update, insert, or delete operations that refer to a view that includes aggregates or row aggregates are not allowed. • insert, delete, and update operations that refer to a distinct view are not allowed. • insert statements are not allowed unless all NOT NULL columns in the underlying tables or views are included in the view through which you are inserting new rows. Adaptive Server has no way to supply values for NOT NULL columns in the underlying objects. • If a view has a with check option clause, all rows inserted or updated through the view (or through any derived views) must satisfy the view’s selection criteria. • delete statements are not allowed on multitable views. • insert statements are not allowed on multitable views created with the with check option clause. • update statements are allowed on multitable views where with check option is used. The update fails if any of the affected columns appears in the where clause, in an expression that includes columns from more than one table. • insert and update statements are not allowed on multitable distinct views.CHAPTER 10 Views: Limiting Access to Data Transact-SQL User’s Guide 365 • update statements cannot specify a value for an IDENTITY column. The table owner, Database Owner, or a System Administrator can insert an explicit value into an IDENTITY column after setting identity_insert on for the column’s base table. • If you insert or update a row through a multitable view, all affected columns must belong to the same base table. • writetext is not allowed on the text and image columns in a view. When you attempt an update, insert, or delete for a view, Adaptive Server checks to make sure that none of the above restrictions is violated and that no data integrity rules are violated. Restrictions on updating views Restrictions on updated views apply to these areas: • Computed columns in a view definition • group by or compute in a view definition • Null values in underlying objects • Views created using with check option • Multitable views • Views with IDENTITY columns Computed columns in a view definition This restriction applies to columns of views that are derived from computed columns or built-in functions. For example, the amt_due column in the view accounts is a computed column. create view accounts (title_id, advance, amt_due) as select titles.title_id, advance, (price * royalty/100) * total_sales from titles, roysched where price > $15 and advance > $5000 and titles.title_id = roysched.title_id and total_sales between lorange and hirange The rows visible through accounts are: select * from accountsModifying data through views 366 Adaptive Server Enterprise title_id advance amt_due -------- -------- --------- PC1035 7,000.00 32,240.16 PC8888 8,000.00 8,190.00 PS1372 7,000.00 809.63 TC3218 7,000.00 785.63 (4 rows affected) updates and inserts to the amt_due column are not allowed because there is no way to deduce the underlying values for price, royalty, or year-to-date sales from any value you might enter in the amt_due column. delete operations do not make sense because there is no underlying value to delete. group by or compute in a view definition This restriction applies to all columns in views that contain aggregate values— that is, views whose definition includes a group by or compute clause. Here is a view defined with a group by clause and the rows seen through it: create view categories (category, average_price) as select type, avg(price) from titles group by type select * from categories category average_price ------------- ------------- UNDECIDED NULL business 13.73 mod_cook 11.49 popular_comp 21.48 psychology 13.50 trad_cook 15.96 (6 rows affected) It does not make sense to insert rows into the view categories. To what group of underlying rows would an inserted row belong? Updates on the average_price column are not allowed because there is no way to know from any value you might enter there how the underlying prices should be changed. NULL values in underlying objects This restriction applies to insert statements when some NOT NULL columns are contained in the tables or views from which the view is derived. CHAPTER 10 Views: Limiting Access to Data Transact-SQL User’s Guide 367 For example, suppose null values are not allowed in a column of a table that underlies a view. Normally, when you insert new rows through a view, any columns in underlying tables that are not included in the view are given null values. If null values are not allowed in one or more of these columns, no inserts can be allowed through the view. For example, in this view: create view business_titles as select title_id, price, total_sales from titles where type = "business" Null values are not allowed in the title column of the underlying table titles, so no insert statements can be allowed through business_view. Although the title column does not even exist in the view, its prohibition of null values makes any inserts into the view illegal. Similarly, if the title_id column has a unique index, updates or inserts that would duplicate any values in the underlying table are rejected, even if the entry does not duplicate any value in the view. Views created using with check option This restriction determines what types of modifications you can make through views with check options. If a view has a with check option clause, each row inserted or updated through the view must be visible within the view. This is true whether you insert or update the view directly or indirectly, through another derived view. Multitable views This restriction determines what types of modifications you can make through views that join columns from multiple tables. Adaptive Server prohibits delete statements on multitable views, but allows update and insert statements that would not be allowed in other systems. You can insert or update a multitable view if: • The view has no with check option clause. • All columns being inserted or updated belong to the same base table. For example, consider the following view, which includes columns from both titles and publishers and has no with check option clause: create view multitable_viewDropping views 368 Adaptive Server Enterprise as select title, type, titles.pub_id, state from titles, publishers where titles.pub_id = publishers.pub_id A single insert or update statement can specify values either for the columns from titles or for the column from publishers: update multitable_view set type = "user_friendly" where type = "popular_comp" However, this statement fails because it affects columns from both titles and publishers: update multitable_view set type = "cooking_trad", state = "WA" where type = "trad_cook" Views with IDENTITY columns This restriction determines what types of modifications you can make to views that include IDENTITY columns. By definition, IDENTITY columns are not updatable. Updates through a view cannot specify an IDENTITY column value. Inserts to IDENTITY columns are restricted to: • The table owner • The Database Owner or the System Administrator if the table owner has granted them permission • The Database Owner or the System Administrator if impersonating the table owner by using the setuser command. To enable such inserts through a view, use set identity_insert on for the column’s base table. It is not sufficient to use set identity_insert on for the view through which you are inserting. Dropping views To delete a view from the database, use drop view: drop view [owner.]view_name [, [owner.]view_name]... CHAPTER 10 Views: Limiting Access to Data Transact-SQL User’s Guide 369 As indicated, you can drop more than one view at a time. Only its owner (or the database owner) can drop a view. When you issue drop view, information about the view is deleted from sysprocedures, sysobjects, syscolumns, syscomments, sysprotects, and sysdepends. All privileges on that view are also deleted. If a view depends on a table or on another view that has been dropped, Adaptive Server returns an error message if anyone tries to use the view. If a new table or view is created to replace the one that has been dropped, and if it has the same name as the dropped table or view, the view again becomes usable, as long as the columns referenced in the view definition exist. Using views as security mechanisms Permission to access the subset of data in a view must be explicitly granted or revoked, regardless of the permissions in force on the view’s underlying tables. Data in an underlying table that is not included in the view is hidden from users who are authorized to access the view but not the underlying table. For example, you may not want some users to access the columns that have to do with money and sales in the titles table. You can create a view of the titles table that omits those columns, and then give all users permission on the view, and give only the Sales Department permission on the table. For example: revoke all on titles to public grant all on bookview to public grant all on titles to sales For information about how to grant or revoke permissions, see the System Administration Guide. Getting information about views System procedures, catalog stored procedures, and Adaptive Server built-in functions provide information from the system tables about views. For complete information about system procedures, see the Reference Manual.Getting information about views 370 Adaptive Server Enterprise Getting help on views with sp_help You can get a report on a view with sp_help. For example: sp_help hiprice Name Owner type --------- ------ ----- hiprice dbo view (1 row affected) Data_located_on_segment When_created ------------------------------ -------------------- not applicable July 7 1997 11:57AM Column_name Type Length Precision Scale ----------- ------- ------ --------- ----- title_id tid 6 NULL NULL title varchar 80 NULL NULL type char 12 NULL NULL pub_id char 4 NULL NULL price money 8 NULL NULL advance money 8 NULL NULL total_sales int 4 NULL NULL notes varchar 200 NULL NULL pubdate datetime 8 NULL NULL contract bit 1 NULL NULL Nulls Default_name Rule_name Identity ------ ------------ --------- -------- 0 NULL NULL 0 0 NULL NULL 0 0 NULL NULL 0 1 NULL NULL 0 1 NULL NULL 0 1 NULL NULL 0 1 NULL NULL 0 1 NULL NULL 0 0 NULL NULL 0 0 NULL NULL 0 No defined keys for this object. (return status = 0)CHAPTER 10 Views: Limiting Access to Data Transact-SQL User’s Guide 371 Using sp_helptext to display view information The System Security Officer must reset the allow select on syscomments.text column configuration parameter, in the evaluated configuration. (See evaluated configuration in the Glossary for more information.) When this happens, you must be the creator of the view or a System Administrator to view the text of a view through sp_helptext. To display the text of the create view statement, execute sp_helptext: sp_helptext hiprice ---------- 1 (1 row affected) text -------------------------------------------- create view hiprice as select * from titles where price > $15 and advance > $5000 (1 row affected, return status = 0) If the source text of a view was encrypted using sp_hidetext, Adaptive Server displays a message advising you that the text is hidden. For information about hiding source text, see sp_hidetext in the Reference Manual. Using sp_depends to list dependent objects sp_depends lists all the objects that the view or table references in the current database, and all the objects that reference that view or table. sp_depends titles Things inside the current database that reference the object. object type ------------- --------------------------- dbo.history_proc stored procedure dbo.title_proc stored procedure dbo.titleid_proc stored procedure dbo.deltitle trigger dbo.totalsales_trig trigger dbo.accounts view dbo.bookview viewGetting information about views 372 Adaptive Server Enterprise dbo.categories view dbo.hiprice view dbo.multitable_view view dbo.titleview view (return status = 0) Listing all views in a database sp_tables lists all views in a database when used in the following format: sp_tables @table_type = "’VIEW’" Finding an object name and ID The system functions object_id() and object_name() identify the ID and name of a view. For example: select object_id("titleview") ---------- 480004741 Object names and IDs are stored in the sysobjects table. Transact-SQL User’s Guide 373 C H A P T E R 1 1 Using the Built-In Functions in Queries Built-in functions are a Transact-SQL extension to SQL that return information from the database. This chapter discusses: For reference material on the built-in functions, see the Reference Manual. System functions that return database information The system functions return special information from the database. Many of them provide a shorthand way of querying the system tables. The general syntax of the system functions is: select function_name(argument[s]) You can use the system functions in the select list, in the where clause, and anywhere an expression is allowed. For example, to find the user identification number of your coworker who logs in as “harold,” type: select user_id("harold") Assuming that “harold” has user ID 13, the result is: Topic Page System functions that return database information 373 String functions used for character strings or expressions 379 Text functions used for text and image data 389 Aggregate functions 392 Mathematical functions 393 Date functions 396 Datatype conversion functions 402 Security functions 412System functions that return database information 374 Adaptive Server Enterprise ------------- 13 (1 row affected) Generally, the name of the function tells you what kind of information is returned. The system function user_name takes an ID number as its argument and returns the user’s name: select user_name(13) --------- harold (1 row affected) To find the name of the current user, that is, your name, omit the argument: select user_name() --------- dbo (1 row affected) Adaptive Server handles user IDs as follows: • The System Administrator becomes the Database Owner in any database he or she is using by assuming the server user ID 1. • A “guest” user is always given the server user ID 1. • Inside a database, the user_name of the Database Owner is always “dbo”; his or her user ID is 1. • Inside a database, the “guest” user ID is always 2. Table 11-1 lists the name of each system function, the argument it takes, and the result it returns. Table 11-1: System functions, arguments, and results Function Argument Result col_name (object_id, column_id [, database_id ]) Returns the column name. col_length (object_name, column_name) Returns the defined length of column. Use datalength to see the actual data size.Chapter 11 Using the Built-In Functions in Queries Transact-SQL User’s Guide 375 curunreservedpgs (dbid, lstart, unreservedpgs) Returns the number of free pages in a disk piece. If the database is open, the value is taken from memory; if the database is not in use, the value is taken from the unreservedpgs column in sysusages. data_pgs ([dbid,] object_id , {doampg | ioampg }) Returns the number of pages used by the table (doampg) or index (ioampg). The result does not include pages used for internal structures. Use the function in a query run against the sysindexes table. datalength (expression) Returns the length of expression in bytes. expression is usually a column name. If expression is a character constant, it must be enclosed in quotes. db_id ([ database_name]) Returns the database ID number. database_name must be a character expression; if it is a constant expression, it must be enclosed in quotes. If no database_name is supplied, db_id returns the ID number of the current database. db_name ([database_id ]) Returns the database name. database_id must be a numeric expression. If no database_id is supplied, db_name returns the name of the current database. host_id ( ) Returns the host process ID of the client process (not the Adaptive Server process). host_name ( ) Returns the current host computer name of the client process (not the Adaptive Server process). index_col (object_name, index_id , key_ #[, user_id ]) Returns the name of the indexed column; returns NULL if object_name is not a table or view name. isnull (expression1, expression2) Substitutes the value specified in expression2 when expression1 evaluates to NULL.The datatypes of the expressions must convert implicitly, or you must use the convert function. Function Argument Result System functions that return database information 376 Adaptive Server Enterprise lct_admin ({{ "lastchance" | "logfull" | "unsuspend"} , database_id } | "reserve", log_pages }) Manages the log segment’s last-chance threshold. lastchance creates a last-chance threshold in the specified database. logfull returns 1 if the last-chance threshold has been crossed in the specified database, or 0 if it has not. unsuspend awakens suspended tasks in the database and disables the last-chance threshold if that threshold has been crossed. reserve returns the number of free log pages required to successfully dump a transaction log of the specified size. object_id (object_name) Returns the object ID. object_name (object_id [, database_id ]) Returns the object name. reserved_pgs (object_id, {doampg | ioampg}) Returns the number of pages allocated to table or index, including report pages used for internal structures. rowcnt (doampg) Returns the number of rows in a table (estimate). suser_id ([server_user_name]) Returns the server user’s ID number from syslogins. If no server_user_name is supplied, it returns the server ID of the current user. suser_name ([server_user_id]) Returns the server user’s name. Server user’s IDs are stored in syslogins. If no server_user_id is supplied, it returns the name of the current user. tsequal (timestamp, timestamp2 ) Compares timestamp values to prevent update on a row that has been modified since it was selected for browsing. timestamp is the timestamp of the browsed row; timestamp2 is the timestamp of the stored row. Allows you to use browse mode without calling DB-Library. used_pgs (object_id, doampg, ioampg) Returns the total number of pages used by a table and its clustered index. user Returns the user’s name. user_id ([user_name]) Returns the user’s ID number. Reports the number from sysusers in the current database. If no user_name is supplied, it returns the ID of the current user. user_name ([user_id]) Returns the user’s name, based on the user’s ID in the current database. If no user_id is supplied, it returns the name of the current user. Function Argument Result Chapter 11 Using the Built-In Functions in Queries Transact-SQL User’s Guide 377 When the argument to a system function is optional, the current database, host computer, server user, or database user is assumed. With the exception of user, built-in functions are always used with parentheses, even if the argument is NULL. Examples of using system functions The examples in this section use these system functions: • col_length • datalength • isnull • user_name col_length This query finds the length of the title column in the titles table (the “x=” is included so that the result has a column heading): select x = col_length("titles", "title") x -------- 80 (1 row affected) valid_name (character_expression) Returns 0 if the character_expression is not a valid identifier (illegal characters or more than 30 bytes long), or a number other than 0 if it is a valid identifier. valid_user (server_user_id) Returns 1 if the specified ID is a valid user or alias in at least one database on this Adaptive Server. You must have the sa_role or sso_role role to use this function on a server_user_id other than your own. Function Argument Result System functions that return database information 378 Adaptive Server Enterprise datalength In contrast to col_length, which finds the defined length of a column, datalength reports the actual length, in bytes, of the data stored in each row. Use this function on varchar, nvarchar, varbinary, text, and image datatypes, since they can store variable lengths and do not store trailing blanks. datalength of any NULL data returns NULL. When a char value is declared to allow NULLS, Adaptive Server stores it internally as a varchar. All other datatypes report their defined length. Here is an example that finds the length of the pub_name column in the publishers table: select Length = datalength(pub_name), pub_name from publishers Length pub_name ------ ------------------------ 13 New Age Books 16 Binnet & Hardley 20 Algodata Infosystems (3 rows affected) isnull This query finds the average of the prices of all titles, substituting the value “$10.00’’ for all NULL entries in price: select avg(isnull(price,$10.00)) from titles ------------ 14.24 (1 row affected) user_name This query finds the row in sysusers where the name is equal to the result of applying the system function user_name to user ID 1: select name from sysusers where name = user_name(1) name ------------------------ dbo (1 row affected) Chapter 11 Using the Built-In Functions in Queries Transact-SQL User’s Guide 379 String functions used for character strings or expressions String functions are used for various operations on character strings or expressions. A few string functions can be used on binary data as well as on character data. You can also concatenate binary data or character strings or expressions. String built-in functions return values commonly needed for operations on character data. String function names are not keywords. The syntax for string functions takes the general form: select function_name(arguments) You can concatenate binary or character expressions like this: select (expression + expression [+ expression]...) When concatenating noncharacter, nonbinary expressions, you must use the convert function: select "The price is " + convert(varchar(12),price) from titles Most string functions can be used only on char, nchar, unichar , varchar, univarchar, and nvarchar datatypes and on datatypes that implicitly convert to char, unichar, or varchar, univarchar. A few string functions can also be used on binary and varbinary data. patindex can be used on text, char, nchar, varchar, and nvarchar columns. You can concatenate binary and varbinary columns and char, unichar, nchar, varchar, univarchar, and nvarchar columns. If you concatenate unichar and univarchar with char, nchar, nvarchar, and varchar, the result is unichar or univarchar. However, you cannot concatenate text or image columns. You can nest string functions and use them anywhere an expression is allowed. When you use constants with a string function, enclose them in single or double quotes. Each function also accepts arguments that can be implicitly converted to the specified type. For example, functions that accept approximate numeric expressions also accept integer expressions. Adaptive Server automatically converts the argument to the desired type. Table 11-2 lists the arguments used in string functions. If a function takes more than one expression of the same type, the arguments are numbered char_expr1, char_expr2, and so on. String functions used for character strings or expressions 380 Adaptive Server Enterprise Table 11-2: Arguments used in string functions Table 11-3 lists function names, arguments, and results. Table 11-3: String functions, arguments and results Argument type Can be replaced by char_expr A character-type column name, variable, or constant expression of char, unichar, varchar, univarchar, nchar, or nvarchar type. Functions that accept text column names are noted in the explanation. Constant expressions must be enclosed in quotation marks. uchar_expr A character-type column name, variable, or constant expression of unichar or univarchar type. Functions that accept text column names are noted in the explanation. Constant expressions must be enclosed in quotation marks. expression A binary or character column name, variable or constant expression. Can be char, varchar, nchar,, nvarchar, unichar or univarchar data, as for char_expr, plus binary or varbinary. pattern A character expression of char, nchar, varchar, or nvarchar datatype that may include any of the pattern-matching wildcards supported by Adaptive Server. approx_numeric Any approximate numeric (float, real, or double precision) column name, variable, or constant expression. integer_expr Any integer (such as tinyint, smallint or int), column name, variable, or constant expression. Maximum size ranges are noted, as they apply. start An integer_expr. length An integer_expr. Function Argument Result ascii (char_expr) Returns the ASCII code for the first character in the expression. char (integer_expr) Converts a single-byte integer value to a character value. char is usually used as the inverse of ascii. integer_expr must be between 0 and 255. Returns a char datatype. If the resulting value is the first byte of a multibyte character, the character may be undefined. charindex (expression1, expression2) Searches expression2 for the first occurrence of expression1 and returns an integer representing its starting position. If expression1 is not found, it returns 0. If expression1 contains wildcard characters, charindex treats them as literals. char_length (char_expr) Returns an integer representing the number of characters in a character expression or text value. For variable-length data in a table column, char_length returns the number of characters. For fixed-length data, it returns the defined length of the column. For multibyte character sets, the number of characters in the expression is usually less than the number of bytes; use the system function datalength to determine the number of bytes. difference (char_expr1, char_expr2) Returns an integer representing the difference between two soundex values. See soundex, below. lower (char_expr) Converts uppercase to lowercase. Returns a character value.Chapter 11 Using the Built-In Functions in Queries Transact-SQL User’s Guide 381 ltrim (char_expr) Removes leading blanks from the character expression. Only values equivalent to the space character in the SQL special character specification are removed. patindex (“%pattern%”, char_expr [using {bytes | chars | characters}]) Returns an integer representing the starting position of the first occurrence of pattern in the specified character expression; returns 0 if pattern is not found. By default, patindex returns the offset in characters. To return the offset in bytes, that is, multibyte character strings, specify using bytes. The % wildcard character must precede and follow pattern, except when searching for first or last characters. See “Character strings in query results” on page 48 for a description of the wildcard characters that can be used in pattern. patindex can be used on text data. replicate (char_expr, integer_expr) Returns a string with the same datatype as char_expr, containing the same expression repeated the specified number of times or as many times as will fit into a 255-byte space, whichever is less. reverse (expression) Returns the reverse of the character or binary expression; if expression is “abcd”, it returns “dcba”; if expression is 0x12345000, returns 0x00503412. right (expression, integer_expr) Returns the part of the character or binary expression starting at the specified number of characters from the right. Return value has the same datatype as the character expression. rtrim (char_expr) Removes trailing blanks. Only values equivalent to the space character in the SQL special character definition are removed. soundex (char_expr) Returns a four-character soundex code for character strings that are composed of a contiguous sequence of valid single- or double-byte Roman letters. space (integer_expr) Returns a string with the indicated number of single-byte spaces. str (approx_numeric [, length [, decimal] ]) Returns a character representation of the floating point number. length sets the number of characters to be returned (including the decimal point, all digits to the right and left of the decimal point, and blanks); decimal sets the number of decimal digits to be returned. length and decimal are optional. If given, they must be nonnegative. Default length is 10; default decimal is 0. str rounds the decimal portion of the number so that the results fit within the specified length. stuff (char_expr1, start, length, char_expr2) Delete length characters from char_expr1 at start, and then insert char_expr2 into char_expr1 at start. To delete characters without inserting other characters, char_expr2 should be NULL, not ” ”, which indicates a single space. Function Argument ResultString functions used for character strings or expressions 382 Adaptive Server Enterprise Examples of using string functions The examples in this section use these system functions: • charindex, patindex • str substring (expression, start, length) Returns part of a character or binary string. start specifies the character position at which the substring begins. length specifies the number of characters in the substring. to_unichar (integer_expr) Returns a unichar expression having the value of the integer expression. If the integer expression is in the range 0xD800..0xDFFF, a sqlstate exception is raised, an error is printed, and the operation is aborted. If the integer expression is in the range 0..0xFFFF, a single Unicode value is returned. If the integer expression is in the range 0x10000..0x10FFFF, a surrogate pair is returned. upper (char_expr) Converts lowercase to uppercase. Returns a character value. uhighsurr (uchar_expr, start ) Returns 1 if the Unicode value at start is the high half of a surrogate pair (which should appear first in the pair). Otherwise, returns 0. This function allows you to write explicit code for surrogate handling. Particularly, if a substring starts on a Unicode character where uhighsurr() is true, extract a substring of at least 2 Unicode values, as substr() does not extract just 1. substr() does not extract half of a surrogate pair). ulowsurr (uchar_expr, start) Returns 1 if the Unicode value at start is the low half of a surrogate pair (which should appear second in the pair). Otherwise, returns 0. This function allows you to explicitly code around the adjustments performed by substr(), stuff(), and right(). Particularly, if a substring ends on a Unicode value where ulowsurr() is true, extract a substring of 1 less characters (or 1 more), since substr() does not extract a string that contains an unmatched surrogate pair. uscalar (uchar_expr) Returns the Unicode scalar value for the first Unicode character in an expression. If the first character is not the high-order half of a surrogate pair, then the value is in the range 0..0xFFFF. If the first character is the high-order half of a surrogate pair, a second value must be a low-order half, and the return value is in the range 0x10000..0x10FFFF. If this function is called on a uchar_expr containing an unmatched surrogate half, an SQLSTATE exception is raised, an error printed, and the operation aborted. Function Argument ResultChapter 11 Using the Built-In Functions in Queries Transact-SQL User’s Guide 383 • stuff • soundex, difference • substring charindex, patindex The charindex and patindex functions return the starting position of a pattern you specify. Both take two arguments, but they work slightly differently, since patindex can use wildcard characters, but charindex cannot. charindex can be used only on char, nchar, unichar, univarchar, varchar, nvarchar, binary, and varbinary columns; patindex works on char, nchar, unichar, univarchar, varchar, nvarchar, and text columns. Both functions take two arguments. The first is the pattern whose position you want. With patindex, you must include percent signs before and after the pattern, unless you are looking for the pattern as the first (omit the preceding %) or last (omit the trailing %) characters in a column. For charindex, the pattern cannot include wildcard characters. The second argument is a character expression, usually a column name, in which Adaptive Server searches for the specified pattern. To find the position at which the pattern “wonderful” begins in a certain row of the notes column of the titles table, using both functions, enter: select charindex("wonderful", notes), patindex("%wonderful%", notes) from titles where title_id = "TC3218" ------------- ------------- 46 46 (1 row affected) If you do not restrict the rows to be searched, the query returns all rows in the table and reports zero values for those rows that do not contain the pattern. In the following example, patindex finds all the rows in sysobjects that start with “sys” and whose fourth character is “a”, “b”, “c”, or “d”: select name from sysobjects where patindex("sys[a-d]%", name) > 0 name ------------------------------ sysalternates sysattributesString functions used for character strings or expressions 384 Adaptive Server Enterprise syscolumns syscomments sysconstraints sysdepends (6 rows affected) str The str function converts numbers to characters, with optional arguments for specifying the length of the number (including sign, decimal point, and digits to the right and left of the decimal point), and the number of places after the decimal point. Set length and decimal arguments to str positive. The default length is 10. The default decimal is 0. The length should be long enough to accommodate the decimal point and the number’s sign. The decimal portion of the result is rounded to fit within the specified length. If the integer portion of the number does not fit within the length, however, str returns a row of asterisks of the specified length. For example: select str(123.456, 2, 4) -- ** (1 row affected) A short approx_numeric is right-justified in the specified length, and a long approx_numeric is truncated to the specified number of decimal places. stuff The stuff function inserts a string into another string. It deletes a specified length of characters in expr1 at the start position. It then inserts expr2 string into expr1 string at the start position. If the start position or the length is negative, a NULL string is returned. If the start position is longer than expr1, a NULL string is returned. If the length to delete is longer than expr1, it is deleted through the last character in expr1. For example: select stuff("abc", 2, 3, "xyz") ---- Chapter 11 Using the Built-In Functions in Queries Transact-SQL User’s Guide 385 axyz (1 row affected) To use stuff to delete a character, replace expr2 with NULL, not with empty quotation marks. Using “ ” to specify a null character replaces it with a space. select stuff("abcdef", 2, 3, null) --- aef (1 row affected) select stuff("abcdef", 2, 3, "") ---- a ef (1 row affected) soundex, difference The soundex function converts a character string to a four-digit code for use in a comparison. It ignores vowels in the comparison. Nonalphabetic characters terminate the soundex evaluation. This function always returns some value. These two names have identical soundex codes: select soundex ("smith"), soundex ("smythe") ----- ----- S530 S530 The difference function compares the soundex values of two strings and evaluates the similarity between them, returning a value from 0 to 4. A value of 4 is the best match. For example: select difference("smithers", "smothers") --------- 4 (1 row affected) select difference("smothers", "brothers") --------- 2 (1 row affected)String functions used for character strings or expressions 386 Adaptive Server Enterprise substring The following example uses the substring function. It displays the last name and first initial of each author, for example, “Bennet A”. select au_lname, substring(au_fname, 1, 1) from authors substring returns a portion of a character or binary string. substring always takes three arguments. The first can be a character or binary string, a column name, or a string-valued expression that includes a column name. The second argument specifies the position at which the substring should begin. The third specifies the length, in number of characters, of the string to be returned. The syntax of substring looks like this: substring(expression, start, length) For example, here is how to specify the second, third, and fourth characters of the string constant “abcdef”: select x = substring("abcdef", 2, 3) x --------- bcd (1 row affected) The following example shows how to extract the lower four digits from a binary field, where each position represents two binary digits: select substring(xactid,5,2) from syslogs ------ 0x0000 0x0001 0x0001 0x0001 0x0001 0x0001 0x0001 0x0001 0x0001 0x0001 0x0001 (11 rows affected)Chapter 11 Using the Built-In Functions in Queries Transact-SQL User’s Guide 387 Examples of other string functions Most of the remaining string functions are easy to use and understand. Table 11-4: String function examples Concatenation You can concatenate binary or character expressions—combine two or more character or binary strings, character or binary data, or a combination of them—with the + string concatenation operator. The maximum length of a concatenated string is 16384 bytes. When you concatenate character strings, enclose each character expression in single or double quotes. The concatenation syntax is: select (expression + expression [+ expression]...) Here is how to combine two character strings: select ("abc" + "def") ------- abcdef (1 row affected) This query displays California authors’ names under the column heading Moniker in last name-first name order, with a comma and space after the last name: select Moniker = (au_lname + ", " + au_fname) from authors where state = "CA" Moniker ------------------------------------------------- White, Johnson Green, Marjorie Statement Result select right("abcde", 3) cde select right("abcde", 6) abcde select right(0x12345000, 3) 0x345000 select right(0x12345000, 6) 0x12345000 select upper("torso") TORSO select ascii("ABC") 65String functions used for character strings or expressions 388 Adaptive Server Enterprise Carson, Cheryl O’Leary, Michael Straight, Dick Bennet, Abraham Dull, Ann Gringlesby, Burt Locksley, Chastity Yokomoto, Akiko Stringer, Dirk MacFeather, Stearns Karsen, Livia Hunter, Sheryl McBadden, Heather (15 rows affected) To concatenate numeric or datetime datatypes, you must use the convert function: select "The due date is " + convert(varchar(30), pubdate) from titles where title_id = "BU1032" --------------------------------------- The due date is Jun 12 1986 12:00AM (1 row affected) Concatenation and the empty string Adaptive Server evaluates the empty string (““ or ‘’) as a single space. This statement: select "abc" + "" + "def" produces: abc def Nested string functions You can nest string functions. For example, to display the last name and the first initial of each author, with a comma after the last name and a period after the first name, type: select (au_lname + "," + " " + substring(au_fname, 1, Chapter 11 Using the Built-In Functions in Queries Transact-SQL User’s Guide 389 1) + ".") from authors where city = "Oakland" -------------------------------------------- Green, M. Straight, D. Stringer, D. MacFeather, S. Karsen, L. (5 rows affected) To display the pub_id and the first two characters of each title_id for books priced more than $20, type: select substring(pub_id + title_id, 1, 6) from titles where price > $20 -------------- 1389PC 0877PS 0877TC (3 rows affected) Text functions used for text and image data Text built-in functions are used for operations on text and image data. Table 11- 5 lists text function names, arguments, and results: Table 11-5: Built-in text functions for text and image data Function Argument Result patindex (“%pattern%”, char_expr [using {bytes | chars | characters} ] ) Returns an integer value representing the starting position of the first occurrence of pattern in the specified character expression; returns 0 if pattern is not found. By default, patindex returns the offset in characters; to return the offset in bytes for multibyte character strings, specify using bytes. The % wildcard character must precede and follow pattern, except when you are searching for first or last characters. See “Character strings in query results” on page 48 for a description of the wildcard characters that can be used in pattern.Text functions used for text and image data 390 Adaptive Server Enterprise datalength also works on text columns. See “System functions that return database information” on page 373 for information about datalength. The set textsize command specifies the limit, in bytes, of the text or image data to be returned with a select statement. For example, this command sets the limit on text or image data returned with a select statement to 100 bytes: set textsize 100 The current setting is stored in the @@textsize global variable. The default setting is controlled by the client program. To reset the default, issue: set textsize 0 You can also use the @@textcolid, @@textdbid, @@textobjid, @@textptr, and @@textsize global variables to manipulate text and image data. Readtext The readtext command provides a way to retrieve text and image values if you want to retrieve only a selected portion of a column’s data. readtext requires the name of the table and column, the text pointer, a starting offset within the column, and the number of characters or bytes to retrieve. The full syntax of readtext is: readtext [[database.]owner.]table_name.column_name text_pointer offset size [holdlock | noholdlock] [readpast] [using {bytes | chars | characters}] [at isolation { [read uncommitted | 0] | [read committed | 1] | [repeatable read | 2] | [serializable | 3]}] textptr (text_columname) Returns the text pointer value, a 16-byte varbinary value. textvalid (“table_name..col_name”, textpointer) Checks that a given text pointer is valid. Note that the identifier for a text or image column must include the table name. Returns 1 if the pointer is valid, 0 if the pointer is invalid. Function Argument ResultChapter 11 Using the Built-In Functions in Queries Transact-SQL User’s Guide 391 The holdlock flag locks the text value for reads until the end of the transaction. Other users can read the value but cannot modify it. The at isolation clause is described in Chapter 19, “Transactions: Maintaining Data Consistency and Recovery.” If you are using a multibyte character set, the using option allows you to choose whether you want readtext to interpret the offset and size as bytes or as characters. Both chars and characters specify characters. This option has no effect when used with a single-byte character set or with image values (readtext reads image values only on a byte-by-byte basis). If the using option is not given, readtext returns the value as if bytes were specified. Adaptive Server has to determine the number of bytes to send to the client in response to a readtext command. When the offset and size are in bytes, determining the number of bytes in the returned text is simple. When the offset and size are in characters, Adaptive Server must calculate the number of bytes being returned to the client. As a result, performance may be slower when using characters as the offset and size. using characters is useful only when Adaptive Server is using a multibyte character set. This option ensures that readtext does not return partial characters. When using bytes as the offset, Adaptive Server may find partial characters at the beginning or end of the text data to be returned. If it does, the server replaces each partial character with question marks before returning the text to the client. You cannot use readtext on text and image columns in views. Examples of using text functions This example uses the textptr function to locate the text column, copy, associated with title_id BU7832 in table blurbs. The text pointer, a 16-byte binary string, is put into a local variable, @val, and supplied as a parameter to the readtext command. readtext returns 5 bytes starting at the second byte, with an offset of 1. declare @val binary(16) select @val = textptr(copy) from blurbs where au_id = "486-29-1786" readtext blurbs.copy @val 1 5 textptr returns a 16-byte varbinary string. Sybase suggests that you put this string into a local variable, as in the preceding example, and use it by reference. Aggregate functions 392 Adaptive Server Enterprise An alternative to using textptr in the preceding declare example is the @@textptr global variable: readtext texttest.blurb @@textptr 1 5 The value of @@textptr is set from the last insert or update to any text or image field by the current Adaptive Server process. Inserts and updates by other processes do not affect the current process. Explicit conversion using the convert function is supported from text to char, nchar, unichar, varchar, univarchar, or nvarchar, and from image to varbinary or binary, but text or image data is truncated to the server page size. Conversion of text or image to datatypes other than these is not supported, implicitly or explicitly. Aggregate functions The aggregate functions generate summary values that appear as new columns in the query results. Table 11-6 lists the aggregate functions, their arguments, and the results they return. Table 11-6: Aggregate functions Examples are as follows: select avg(advance), sum(total_sales) from titles where type = "business" ------------------------ ----------- 6281.25 30,788 (1 row affected) select count(distinct city) from authors ----------- 16 Function Argument Result avg (all | distinct) expression Returns the numeric average of all (distinct) values count (all | distinct) expression Returns the number of (distinct) non-null values or the number of rows max (expression) Returns the highest value in an expression min (expression) Returns the lowest value in a column sum (all | distinct) expression Returns the total of the valuesChapter 11 Using the Built-In Functions in Queries Transact-SQL User’s Guide 393 (1 row affected) select discount from salesdetail compute max(discount) discount -------------------- 40.000000 ... 46.700000 Compute Result: -------------------- 62.200000 (117 rows affect) select min(au_lname) from authors --------------------- Bennet (1 row affected) Mathematical functions Mathematical built-in functions return values commonly needed for operations on mathematical data. The mathematical functions take the general form: function_name(arguments) The chart below lists the types of arguments that are used in the built-in mathematical functions: Table 11-7: Arguments used in mathematical functions Argument type Can be replaced by approx_numeric Any approximate numeric (float, real, or double precision) column name, variable, constant expression, or a combination of these integer Any integer (tinyint, smallint or, int) column name, variable, constant expression, or a combination of these numeric Any exact numeric (numeric, dec, decimal, tinyint, smallint, or int), approximate numeric (float, real, or double precision), or money column, variable, constant expression, or a combination of these power Any exact numeric, approximate numeric, or money column, variable, or constant expression, or a combination of theseMathematical functions 394 Adaptive Server Enterprise Each function also accepts arguments that can be implicitly converted to the specified type. For example, functions that accept approximate numeric types also accept integer types. Adaptive Server converts the argument to the desired type. If a function takes more than one expression of the same type, the expressions are numbered (for example, approx_numeric1, approx_numeric2). Table 11-8 lists the mathematical functions, their arguments, and the results they return: Table 11-8: Mathematical functions Function Argument Result abs (numeric) Returns the absolute value of a given expression. Results are of the same type, and have the same precision and scale, as the numeric expression. acos (approx_numeric) Returns the angle (in radians) whose cosine is the specified value. asin (approx_numeric) Returns the angle (in radians) whose sine is the specified value. atan (approx_numeric) Returns the angle (in radians) whose tangent is the specified value. atn2 (approx_numeric1, approx_numeric2) Returns the angle (in radians) whose tangent is (approx_numeric1/approx_numeric2). ceiling (numeric) Returns the smallest integer greater than or equal to the specified value. Results are of the same type as the numeric expression. For numeric and decimal expressions, the results have a precision equal to that of the expression and a scale of 0. cos (approx_numeric) Returns the trigonometric cosine of the specified angle (in radians). cot (approx_numeric) Returns the trigonometric cotangent of the specified angle (in radians). degrees (numeric) Converts radians to degrees. Results are of the same type as the numeric expression. For numeric and decimal expressions, the results have an internal precision of 77 and a scale equal to that of the expression. When the money datatype is used, internal conversion to float may cause loss of precision. exp (approx_numeric) Returns the exponential value of the specified value. floor (numeric) Returns the largest integer that is less than or equal to the specified value. Results are of the same type as the numeric expression. For expressions of type numeric or decimal, the results have a precision equal to that of the expression and a scale of 0. log (approx_numeric) Returns the natural logarithm of the specified value. log10 (approx_numeric) Returns the base 10 logarithm of the specified value. pi () Returns the constant value of 3.1415926535897931. power (numeric, power) Returns the value of numeric to the power of power. Results are of the same type as numeric. For expressions of type numeric or decimal, the results have a precision of 77 and a scale equal to that of the expression. Chapter 11 Using the Built-In Functions in Queries Transact-SQL User’s Guide 395 Examples of using mathematical functions The mathematical built-in functions operate on numeric data. Certain functions require integer data and others approximate numeric data. A number of functions operate on exact numeric, approximate numeric, money, and float types. The precision of built-in operations on float type data is six decimal places by default. Error traps are provided to handle domain or range errors of the mathematical functions. Users can set the arithabort and arithignore options to determine how domain errors are handled. For more information about these options, see “Conversion errors” on page 408. Table 11-9 displays some simple examples of mathematical functions: radians (numeric_expr) Converts degrees to radians. Results are of the same type as numeric. For expressions of type numeric or decimal, the results have an internal precision of 77 and a scale equal to that of the numeric expression. When the money datatype is used, internal conversion to float may cause loss of precision. rand ([integer]) Returns a random float value between 0 and 1, using the optional integer as a seed value. round (numeric, integer) Rounds the numeric so that it has integer significant digits. A positive integer determines the number of significant digits to the right of the decimal point; a negative integer, the number of significant digits to the left of the decimal point. Results are of the same type as the numeric expression and, for numeric and decimal expressions, have an internal precision equal to the precision of the first argument plus 1 and a scale equal to that of the numeric expression. sign (numeric) Returns the sign of numeric: positive (+1), zero (0), or negative (-1). Results are of the same type and have the same precision and scale as the numeric expression. sin (approx_numeric) Returns the trigonometric sine of the specified angle (measured in radians). sqrt (approx_numeric) Returns the square root of the specified value. Value must be positive or 0. tan (approx_numeric) Returns the trigonometric tangent of the specified angle (measured in radians). Function Argument Result Date functions 396 Adaptive Server Enterprise Table 11-9: Examples of mathematical functions The round(numeric, integer) function always returns a value. If integer is negative and exceeds the number of significant digits in numeric, Adaptive Server rounds only the most significant digit. For example, this returns a value of 100.00: select round(55.55, -3) The number of zeros to the right of the decimal point is equal to the scale of the first argument’s precision plus 1. Date functions The date built-in functions perform arithmetic operations and display information about datetime, smalldatetime, date and time values. Adaptive Server stores values with the datetime datatype internally as two fourbyte integers. The first four bytes store the number of days before or after the base date, January 1, 1900. The base date is the system’s reference date. datetime values earlier than January 1, 1753 are not permitted. The other four bytes of the internal datetime representation store the time of day to an accuracy of 1/300 second. Statement Result select floor(123) select floor(123.45) select floor(1.2345E2) select floor(-123.45) select floor(-1.2345E2) select floor($123.45) 123 123.000000 123.000000 -124.000000 -124.000000 123.00 select ceiling(123.45) select ceiling(-123.45) select ceiling(1.2345E2) select ceiling(-1.2345E2) select ceiling($123.45) 124.000000 -123.000000 124.000000 -123.000000 124.00 select round(123.4545, 2) select round(123.45, -2) select round(1.2345E2, 2) select round(1.2345E2, -2) 123.4500 100.00 123.450000 100.000000Chapter 11 Using the Built-In Functions in Queries Transact-SQL User’s Guide 397 The date datatype is stored as four bytes. The base date is January 1, 0001 through December 31, 9999. The time datatype covers time from 12:00:00AM through 11:59:59:999PM. The smalldatetime datatype stores dates and times of day with less precision than datetime. smalldatetime values are stored as two two-byte integers. The first two bytes store the number of days after January 1, 1900. The other two bytes store the number of minutes since midnight. Dates range from January 1, 1900 to June 6, 2079, with accuracy to the minute. The default display format for dates looks like this: Apr 15 1997 10:23PM See “Using the general purpose conversion function: convert” on page 403 for information on changing the display format for datetime or smalldatetime. When you enter datetime, smalldatetime, date and time values, enclose them in single or double quotes. Adaptive Server may round or truncate millisecond values. Adaptive Server recognizes a wide variety of datetime data entry formats. For more information about datetime, smalldatetime, date and time values, see Chapter 8, “Creating Databases and Tables,” and Chapter 9, “Adding, Changing, and Deleting Data.” Table 11-10 lists the date functions and the results they produce: Table 11-10: Date functions The datename, datepart, datediff, and dateadd functions take as arguments a date part—the year, month, hour, and so on. The datename function produces ASCII values where appropriate, such as for the day of the week. Function Argument Result getdate () Current system date and time datename (datepart, date) Part of a datetime, smalldatetime, date or time value as an ASCII string datepart (datepart, date) Part of a datetime, smalldatetime, date or time value (for example, the month) as an integer datediff (datepart, date, date) The amount of time between the second and first of two dates, converted to the specified date part (for example, months, days, hours) dateadd (datepart, number, date) A date produced by adding date parts to another dateDate functions 398 Adaptive Server Enterprise datepart returns a number that follows ISO standard 8601, which defines the first day of the week and the first week of the year. Depending on whether the datepart function includes a value for calweekofyear, calyearofweek, or caldayofweek, the date returned may be different for the same unit of time. For example, if Adaptive Server is configured to use US English as the default language: datepart(cyr, "1/1/1989") returns 1988, but: datepart(yy, "1/1/1989) returns 1989. This disparity occurs because the ISO standard defines the first week of the year as the first week that includes a Thursday and begins with Monday. For servers using US English as their default language, the first day of the week is Sunday, and the first week of the year is the week that contains January 4th. Table 11-11 lists each date part, its abbreviation (if there is one), and the possible integer values for that date part. Table 11-11: Date parts select datename (mm, "1997/06/16") ----------- June (1 row affected) select datediff (yy, "1984", "1997") Date Part Abbreviation Values year yy 1753–9999 quarter qq 1–4 month mm 1–12 week wk 1–54 day dd 1–31 dayofyear dy 1–366 weekday dw 1– 7 (Sunday–Saturday) hour hh 0–23 minute mi 0–59 second ss 0–59 millisecond ms 0–999 Chapter 11 Using the Built-In Functions in Queries Transact-SQL User’s Guide 399 ----------- 13 (1 row affected) select dateadd (dd, 16, "1997/06/16") ------------------------------ Jul 2 1997 12:00AM (1 row affected) Note The values of weekday are affected by the language setting. Some examples of the week date part: select datepart(cwk,"1997/01/31") ----------- 5 (1 row affected) select datepart(cyr,"1997/01/15") ----------- 1997 (1 row affected) select datepart(cdw,"1997/01/24") ----------- 5 (1 row affected) Table 11-12 lists the week number date parts, their abbreviations, and values: Table 11-12: Week number date parts Get current date: getdate The getdate function produces the current date and time in Adaptive Server internal format for datetime values. getdate takes the NULL argument, (). Date part Abbreviation Values calweekofyear cwk 1–52 calyearofweek cyr 1753–9999 caldayofweek cdw 1–7 (1 is Monday in us_english)Date functions 400 Adaptive Server Enterprise To find the current system date and time, type: select getdate() -------------------------- Aug 19 1997 12:45PM (1 row affected) You might use getdate in designing a report so that the current date and time are printed every time the report is produced. getdate is also useful for functions such as logging the time a transaction occurred on an account. To display the date using milliseconds, use the convert function. For example: select convert(char(26), getdate(), 109) -------------------------- Aug 19 1997 12:45:59:650PM (1 row affected) See “Changing the display format for dates” on page 410 for more information. Find date parts as numbers or names The datepart and datename functions produce the specified part of a datetime, smalldatetime or date value—the year, quarter, day, hour, and so on—as either an integer or an ASCII string. Since smalldatetime is accurate only to the minute, when a smalldatetime value is used with either of these functions, seconds and milliseconds are always 0. If the time datatype is used, seconds and milleseconds are given. The following examples assume an August 12 date: select datepart(month, getdate()) -------------- 8 (1 row affected) select datename(month, getdate()) ------------- August (1 row affected)Chapter 11 Using the Built-In Functions in Queries Transact-SQL User’s Guide 401 Calculate intervals or increment dates The datediff function calculates the amount of time in date parts between the first and second of the two dates you specify—in other words, it finds the interval between the two dates. The result is a signed integer value equal to date2 - date1 in date parts. This query uses the date November 30, 1990 and finds the number of days that elapsed between pubdate and that date: select pubdate, newdate = datediff(day, pubdate, "Nov 30 1990") from titles For the rows in the titles table having a pubdate of October 21, 1990, the result produced by the previous query is 40, the number of days between October 21 and November 30. To calculate an interval in months, the query is: select pubdate, interval = datediff(month, pubdate, "Nov 30 1990") from titles This query produces a value of 1 for the rows with a pubdate in October 1990 and a value of 5 for the rows with a pubdate in June 1990. When the first date in the datediff function is later than the second date, the resulting value is negative. Since two of the rows in titles have values for pubdate that are assigned using the getdate function as a default, these values are set to the date that your pubs database was created and return negative values (-65) in the two preceding queries. If one or both of the date arguments is a smalldatetime value, they are converted to datetime values internally for the calculation. Seconds and milliseconds in smalldatetime values are automatically set to 0 for the purpose of calculating the difference. Add date interval: dateadd The dateadd function adds an interval (specified as a integer) to a date you specify. For example, if the publication dates of all the books in the titles table slipped three days, you could get the new publication dates with this statement: select dateadd(day, 3, pubdate) from titles ------------------- Jun 15 1986 12:00AM Jun 12 1988 12:00AMDatatype conversion functions 402 Adaptive Server Enterprise Jul 3 1985 12:00AM Jun 25 1987 12:00AM Jun 12 1989 12:00AM Jun 21 1985 12:00AM Jul 6 1997 1:43PM Jul 3 1986 12:00AM Jun 15 1987 12:00AM Jul 6 1997 1:43PM Oct 24 1990 12:00AM Jun 18 1989 12:00AM Oct 8 1990 12:00AM Jun 15 1988 12:00AM Jun 15 1988 12:00AM Oct 24 1990 12:00AM Jun 15 1985 12:00AM Jun 15 1987 12:00AM (18 rows affected) If the date argument is given as a smalldatetime, the result is also a smalldatetime. You can use dateadd to add seconds or milliseconds to a smalldatetime, but it is meaningful only if the result date returned by dateadd changes by at least one minute. Datatype conversion functions Datatype conversions change an expression from one datatype to another and reformat date and time information. Adaptive Server provides three datatype conversion functions, convert, inttohex, and hextoint. Adaptive Server performs certain datatype conversions automatically. These are called implicit conversions. For example, if you compare a char expression and a datetime expression, or a smallint expression and an int expression, or char expressions of different lengths, Adaptive Server automatically converts one datatype to another. Another example, when a datetime value is converted to a date value, the time portion will be truncated leaving only the date portion. If a time value is converted to a datetime value, a default date portion of Jan 1, 1900 will be added to the new datetime value. If a date value is converted to a datetime value, a default time portion of 00:00:00:000 will be added to the datetime value.Chapter 11 Using the Built-In Functions in Queries Transact-SQL User’s Guide 403 You must request other datatype conversions explicitly, using one of the builtin datatype conversion functions. For example, before concatenating numeric expressions, you must convert them to character expressions. If you attempt to explicitly convert a date to a datetime and the value is outside the datetime range such as “Jan 1, 1000” the conversion is not allowed and an error message is given. Adaptive Server does not allow you to convert certain datatypes to certain other datatypes, either implicitly or explicitly. For example, you cannot convert smallint data to datetime or datetime data to smallint. Unsupported conversions result in error messages. Using the general purpose conversion function: convert The general conversion function, convert, converts between a variety of datatypes and specifies a new display format for date and time information. Its syntax is: convert(datatype, expression [, style] ) Here is an example that uses convert in the select list: select title, convert(char(5), total_sales) from titles where type = "trad_cook" title ------------------------------------ ----- Onions, Leeks, and Garlic: Cooking Secrets of the Mediterranean 375 Fifty Years in Buckingham Palace Kitchens 15096 Sushi, Anyone? 4095 (3 rows affected) In the following example, the total_sales column, an int column, is converted to a char(5) column so that it can be used with the like keyword: select title, total_sales from titles where convert(char(5), total_sales) like "15%" and type = "trad_cook" title --------------------------------- ----- Fifty Years in Buckingham Palace Kitchens 15096 Datatype conversion functions 404 Adaptive Server Enterprise (1 row affected) Certain datatypes expect either a length or a precision and scale. If you do not specify a length, Adaptive Server uses the default length of 30 for character and binary data. If you do not specify a precision or scale, Adaptive Server uses the defaults of 18 and 0, respectively. Conversion rules The following sections describe the rules Adaptive Server observes when converting different types of information. Converting character data to a noncharacter type Character data can be converted to a noncharacter type—such as a money, date and time, exact numeric, or approximate numeric type—if it consists entirely of characters that are valid for the new type. Leading blanks are ignored. However, if a char expression that consists of a blank or blanks is converted to a datetime expression, Adaptive Server converts the blanks into the Sybase default datetime value of “Jan 1, 1900”. Adaptive Server generates syntax errors if the data includes unacceptable characters. The following types of characters cause syntax errors: • Commas or decimal points in integer data • Commas in monetary data • Letters in exact or approximate numeric data or bit-stream data • Misspelled month names in date and time data Implicit conversions between unichar/univarchar and datetime/smalldatetime are supported. Converting from one character type to another When you convert from a multibyte character set to a single-byte character set, characters with no single-byte equivalent are converted to blanks. text columns can be explicitly converted to char, nchar, unichar, varchar, univarchar, or nvarchar. You are limited to the maximum length of the character datatypes, the page size. If you do not specify the length, the converted value has a default length of 30 bytes.Chapter 11 Using the Built-In Functions in Queries Transact-SQL User’s Guide 405 Converting numbers to a character type You can convert exact and approximate numeric data to a character type. If the new type is too short to accommodate the entire string, an insufficient space error is generated. For example, the following conversion tries to store a five-character string in a one-character type: select convert(char(1), 12.34) It fails because the char datatype is limited to one character, and the numeric 12.34 requires five characters for the conversion to be successful. Rounding during conversion to or from money types The money and smallmoney types store four digits to the right of the decimal point, but round up to the nearest hundredth (.01) for display purposes. When data is converted to a money type, it is rounded up to four decimal places. Data converted from a money type follows the same rounding behavior if possible. If the new type is an exact numeric with less than 3 decimal places, the data is rounded to the scale of the new type. For example, when $4.50 is converted to an integer, it yields 5: select convert(int, $4.50) ----------- 5 (1 row affected) Adaptive Server assumes that data converted to money or smallmoney is in full currency units, such as dollars, rather than in fractional units, such as cents. For example, the integer value of five is converted to the money equivalent of five dollars, not five cents, in us_english. Converting date and time information Data that is recognizable as a date can be converted to datetime, smalldatetime, date or time. Incorrect month names lead to syntax errors. Dates that fall outside the acceptable range for the datatype lead to arithmetic overflow errors. When datetime values are converted to smalldatetime, they are rounded up to the nearest minute.Datatype conversion functions 406 Adaptive Server Enterprise Converting between numeric types Data can be converted from one numeric type to another. If the new type is an exact numeric whose precision or scale is not sufficient to hold the data, errors can occur. Use the arithabort and arithignore options to determine how these errors are handled. Note The arithabort and arithignore options were redefined in SQL Server release 10.0. If you use these options in your applications, examine them to make sure they are still functioning correctly. Converting binary-like data Adaptive Server binary and varbinary data is platform-specific; the type of hardware you are using determines how the data is stored and interpreted. Some platforms consider the first byte after the “0x” prefix to be the most significant; others consider the first byte to be the least significant. The convert function treats Sybase binary data as a string of characters, rather than as numeric information. convert takes no account of byte order significance when converting a binary expression to an integer or an integer expression to a binary value. Because of this, conversion results can vary from one platform to another. Before converting a binary string to an integer, convert strips it of its “0x” prefix. If the string consists of an odd number of digits, Adaptive Server inserts a leading zero. If the data is too long for the integer type, convert truncates it. If the data is too short, convert adds leading zeros to make it even, and then pads it with zeros on the right. Suppose you want to convert the string 0x00000100 to an integer. On some platforms, this string represents the number 1; on others, the number 256. Depending on which platform executes the function, convert returns either 1 or 256. Converting hexadecimal data For conversion results that are reliable across platforms, use the hextoint and inttohex functions.Chapter 11 Using the Built-In Functions in Queries Transact-SQL User’s Guide 407 hextoint accepts literals or variables consisting of digits and the uppercase and lowercase letters A–F, with or without a “0x” prefix. The following are all valid uses of hextoint: select hextoint("0x00000100FFFFF") select hextoint("0x00000100") select hextoint("100") hextoint strips it of the “0x” prefix. If the data exceeds 8 digits, hextoint truncates it. If the data is less than 8 digits, hextoint right-justifies and pads it with zeros. Then hextoint returns the platform-independent integer equivalent. The above expressions all return the same value, 256, regardless of the platform that executes the hextoint function. The inttohex function accepts integer data and returns an 8-character hexadecimal string without a “0x” prefix. inttohex always returns the same results, regardless of which platform you are using. Converting image data to binary or varbinary Use the convert function to convert an image column to binary or varbinary. You are limited to the maximum length of the binary datatypes, which is the page size of the server. If you do not specify the length, the converted value has a default length of 30 characters. Converting between binary and numeric or decimal types In binary and varbinary data strings, the first two digits after “0x” represent the binary type: “00” represents a positive number and “01” represents a negative number. When you convert a binary or varbinary type to numeric or decimal, be sure to specify the “00” or “01” values after the “0x” digit; otherwise, the conversion will fail. For example, here is how to convert the following binary data to numeric: select convert(numeric (38, 18),0x000000000000000006b14bd1e6eea0000000000000000000 000000000000) ---------------------- 123.456000000000000000 This example converts the same numeric data back to binary: select convert(binary,convert(numeric(38, 18), 123.456))Datatype conversion functions 408 Adaptive Server Enterprise ------------------------------------------------------ -------- 0x000000000000000006b14bd1e6eea00000000000000000000000 00000000 Conversion errors This sections describes the types of errors that can occur during datatype conversions. Arithmetic overflow and divide-by-zero errors Divide-by-zero errors occur when Adaptive Server tries to divide a numeric value by zero. Arithmetic overflow errors occur when the new type has too few decimal places to accommodate the results. This happens during: • Explicit or implicit conversions to exact types with a lower precision or scale • Explicit or implicit conversions of data that falls outside the acceptable range for a money or datetime type • Conversions of strings longer than 4 bytes using hextoint Both arithmetic overflow and divide-by-zero errors are considered serious, whether they occur during implicit or explicit conversions. Use the arithabort arith_overflow option to determine how Adaptive Server handles these errors. The default setting, arithabort arith_overflow on, rolls back the entire transaction in which the error occurs. If you set arithabort arith_overflow off, Adaptive Server aborts the statement that causes the error but continues to process other statements in the transaction or batch.You can use the @@error global variable to check statement results. Use the arithignore arith_overflow option to determine whether Adaptive Server displays a message after these errors. The default setting, off, displays a warning message when a divide-by-zero error or a loss of precision occurs. Setting arithignore arith_overflow on suppresses warning messages after these errors. The optional arith_overflow keyword can be omitted without any effect. Chapter 11 Using the Built-In Functions in Queries Transact-SQL User’s Guide 409 Scale errors When an explicit conversion results in a loss of scale, the results are truncated without warning. For example, when you explicitly convert a float, numeric, or decimal type to an integer, Adaptive Server assumes you really want the result to be an integer and truncates all numbers to the right of the decimal point. During implicit conversions to numeric or decimal types, loss of scale generates a scale error. Use the arithabort numeric_truncation option to determine how serious such an error is considered. The default setting, arithabort numeric_truncation on, aborts the statement that causes the error but continues to process other statements in the transaction or batch. If you set arithabort numeric_truncation off, Adaptive Server truncates the query results and continues processing. Domain errors The convert function generates a domain error when the function’s argument falls outside the range over which the function is defined. This should happen very rarely. Conversions between binary and integer types The binary and varbinary types store hexadecimal-like data consisting of a “0x” prefix followed by a string of digits and letters. These strings are interpreted differently by different platforms. For example, the string 0x0000100 represents 65,536 on machines that consider byte 0 most significant and 256 on machines that consider byte 0 least significant. The convert function and implicit conversions Binary types can be converted to integer types either explicitly, with the convert function, or implicitly. The data is stripped of its “0x” prefix and then zeropadded if it is too short for the new type or truncated if it is too long. Both convert and the implicit datatype conversions evaluate binary data differently on different platforms. Therefore, the results may vary from one platform to another. Use the hextoint function for platform-independent conversion of hexadecimal strings to integers and the inttohex function for platform-independent conversion of integers to hexadecimal values.Datatype conversion functions 410 Adaptive Server Enterprise The hextoint function Use the hextoint function for platform-independent conversions of hexadecimal data to integers. hextoint accepts a valid hexadecimal string, with or without the “0x” prefix, enclosed in quotes, or the name of a character-type column or variable. hextoint returns the integer equivalent of the hexadecimal string. The function always returns the same integer equivalent for a given hexadecimal string, regardless of the platform on which it is executed. The inttohex function Use the inttohex function for platform-independent conversions of integers to hexadecimal strings. inttohex accepts any expression that evaluates to an integer. It always returns the same hexadecimal equivalent for a given expression, regardless of the platform on which it is executed. Converting image columns to binary types You can use the convert function to convert an image column to binary or varbinary. You are limited to the maximum length of the binary datatypes, or the page size of the server. If you do not specify the length, the converted value has a default length of 30 characters. Converting other types to bit types Exact and approximate numeric types can be converted to the bit type implicitly. Character types require an explicit convert function. The expression being converted must consist only of digits, a decimal point, a currency symbol, and a plus or minus sign. The presence of other characters generates syntax errors. The bit equivalent of 0 is 0. The bit equivalent of any other number is 1. Changing the display format for dates The style parameter of convert provides a variety of date display formats for converting datetime or smalldatetime data to char or varchar. The number argument you supply as the style parameter determines how the data is displayed. The year can be displayed in either 2 digits or 4 digits. Add 100 to a style value to get a 4-digit year, including the century (yyyy). Chapter 11 Using the Built-In Functions in Queries Transact-SQL User’s Guide 411 Table 10-14 shows the possible values for style and the variety of date formats you can use. When you use style with smalldatetime, the styles that include seconds or milliseconds will show zeros in those positions. Table 11-13: Converting date formats with the style parameter The default values, style 0 or 100, and 9 or 109, always return the century (yyyy). Here is an example of the use of convert’s style parameter: select convert(char(12), getdate(), 3) This converts the current date to style 3, dd/mm/yy. When converting date data to a character type, use style numbers 1 through 7 (101 through 107) or 10 through 12 (110 through 112) in Table 11-13 to specify the display format. The default value is 100 (mon dd yyyy hh:miAM (or PM )). If date data is converted to a style that contains a time portion, that time portion will reflect the default value of zero. Without century (yy) With century (yyyy) Standard Output - 0 or 100 Default mon dd yyyy hh:mm AM (or PM) 1 101 USA mm/dd/yy 2 2 SQL standard yy.mm.dd 3 103 English/French dd/mm/yy 4 104 German dd.mm.yy 5 105 dd-mm-yy 6 106 dd mon yy 7 107 mon dd, yy 8 108 hh:mm:ss - 9 or 109 Default + milliseconds mon dd yyyy hh:mm:sss AM (or PM) 10 110 USA mm-dd-yy 11 111 Japan yy/mm/dd 12 112 ISO yymmdd 13 113 hh:miAM(or PM) 14 114 hh:mi 14 114 hh:mi:ss:mmmAM(or PM) 15 115 hh:mi:ss:mmm N/A 16 or 116 mon dd yyy hh:mi:ssSecurity functions 412 Adaptive Server Enterprise When converting time data to a character type, use style number 8 or 9 (108 or 109) to specify the display format. The default is 100 (mon dd yyyy hh:miAM (or PM)). If time data is converted to a style that contains a date portion, the default date of Jan 1, 1900 will be displayed. Note convert with NULL in the style argument returns the same result as convert with no style argument. For example, select convert(datetime, "01/01/01") ------------ Jan 1 2001 12:00AM select convert(datetime, "01/01/01", NULL) ------------ Jan 1 2001 12:00AM Security functions The security functions return information about security services and userdefined roles. Table 11-14 lists the name of each security function, the argument it takes, and the result it returns. Table 11-14: Security functions Function Argument Result is_sec_service_on (security_service_nm) Determines whether a particular security service is enabled. Returns 1 if the service is enabled. Otherwise, returns 0. mut_excl_roles (“role_1” , “role_2” [, "membership" |"activation"]) Returns information about the level of mutual exclusivity between two roles. proc_role (“role_name” ) Returns 0 if the invoking user does not possess or has not activated the specified role; 1 if the invoking user has activated the specified role; and 2 if the user possesses the specified role directly or indirectly, but has not activated the role. role_contain (["role1 ", "role2 "]) Returns 1 if the first role specified is contained by the second. role_id (“role_name”) Returns the role ID of the specified role name. role_name (role_id ) Returns the role name of the specified role ID. show_role ( ) Returns the login’s current active roles, if any (sa_role, sso_role, oper_role, replication_role, or role_name). If the login has no roles, returns NULL.Chapter 11 Using the Built-In Functions in Queries Transact-SQL User’s Guide 413 For more information about security features and user-defined roles, see the System Administration Guide. show_sec_services ( ) Returns a list of the available security services that are enabled for the current session Function Argument ResultSecurity functions 414 Adaptive Server EnterpriseTransact-SQL User’s Guide 415 C H A P T E R 1 2 Creating Indexes on Tables An index provides quick access to data in a table, based on the values in specified columns. A table can have more than one index. Indexes are transparent to users accessing data from that table; Adaptive Server automatically decides when to use the indexes created for tables. This chapter discusses: For information on how you can design indexes to improve performance, see the Performance and Tuning Guide. How indexes work Indexes help Adaptive Server locate data. They speed up data retrieval by pointing to the location of a table column’s data on disk. For example, suppose you need to run frequent queries using the identification numbers of stores in the stores table. To prevent Adaptive Server from having to search through each row in the table—which can be time-consuming if the stores table contains millions of rows—you could create the following index, entitled stor_id_ind: create index stor_id_ind on stores (stor_id) Topic Page How indexes work 415 Creating indexes 418 Using clustered or nonclustered indexes 423 Specifying index options 425 Dropping indexes 428 Determining what indexes exist on a table 429 Updating statistics about indexes 431How indexes work 416 Adaptive Server Enterprise The stor_id_ind index goes into effect automatically the next time you query the stor_id column in stores. In other words, indexes are transparent to users. SQL includes no syntax for referring to an index in a query. You can only create or drop indexes from a table; Adaptive Server decides whether to use the indexes for each query submitted for that table. As the data in a table changes over time, Adaptive Server may change the table’s indexes to reflect those changes. Again, these changes are transparent to users; Adaptive Server handles this task on its own. Adaptive Server supports the following types of indexes: • Composite indexes – these indexes involve more than one column. Use this type of index when two or more columns are best searched as a unit because of their logical relationship. • Unique indexes – these indexes do not permit any two rows in the specified columns to have the same value. Adaptive Server checks for duplicate values when the index is created (if data already exists) and each time data is added. • Clustered or nonclustered indexes – clustered indexes force Adaptive Server to continually sort and re-sort the rows of a table so that their physical order is always the same as their logical (or indexed) order. You can have only one clustered index per table. Nonclustered indexes do not require the physical order of rows to be the same as their indexed order. Each nonclustered index can provide access to the data in a different sort order. These types of indexes are described in more detail later in this chapter. Comparing the two ways to create indexes You can create indexes on tables either by using the create index statement (described in this chapter) or by using the unique or primary key integrity constraints of the create table command. However, integrity constraints are limited in the following ways: • You cannot create nonunique indexes. • You cannot use the options provided by the create index command to tailor how indexes work. • You can only drop these indexes as a constraint using the alter table statement.CHAPTER 12 Creating Indexes on Tables Transact-SQL User’s Guide 417 If your application requires these features, you should create your indexes using create index. Otherwise, the unique or primary key integrity constraints offer a simpler way to define an index for a table. For information about the unique and primary key constraints, see Chapter 8, “Creating Databases and Tables.” Guidelines for Using Indexes Indexes speed the retrieval of data. Putting an index on a column often makes the difference between a quick response to a query and a long wait. However, building an index takes time and storage space. For example, nonclustered indexes are automatically re-created when a clustered index is rebuilt. Additionally, inserting, deleting, or updating data in indexed columns takes longer than in unindexed columns. However, this cost is usually outweighed by the extent to which indexes improve retrieval performance. When to index Use the following general guidelines: • If you plan to do manual insertions into the IDENTITY column, create a unique index to ensure that the inserts do not assign a value that has already been used. • A column that is often accessed in sorted order, that is, specified in the order by clause, probably should be indexed so that Adaptive Server can take advantage of the indexed order. • Columns that are regularly used in joins should always be indexed, since the system can perform the join faster if the columns are in sorted order. • The column that stores the primary key of the table often has a clustered index, especially if it is frequently joined to columns in other tables. Remember, there can be only one clustered index per table. Creating indexes 418 Adaptive Server Enterprise • A column that is often searched for ranges of values might be a good choice for a clustered index. Once the row with the first value in the range is found, rows with subsequent values are guaranteed to be physically adjacent. A clustered index does not offer as much of an advantage for searches on single values. When not to index In some cases, indexes are not useful: • Columns that are seldom or never referenced in queries do not benefit from indexes, since the system seldom has to search for rows on the basis of values in these columns. • Columns that can have only two or three values, for example, “male” and “female” or “yes” and “no”, get no real advantage from indexes. If the system does have to search an unindexed column, it does so by looking at the rows one by one. The length of time it takes to perform this kind of scan is directly proportional to the number of rows in the table. Creating indexes The simplest form of the create index command is: create index index_name on table_name (column_name) To create an index on the au_id column of the authors table, the command is: create index au_id_ind on authors(au_id) The index name must conform to the rules for identifiers. The column and table name specify the column you want indexed and the table that contains it. You cannot create indexes on columns with bit, text, or image datatypes. You must be the owner of a table to create or drop an index. The owner of a table can create or drop an index at any time, whether or not there is data in the table. Indexes can be created on tables in another database by qualifying the table name.CHAPTER 12 Creating Indexes on Tables Transact-SQL User’s Guide 419 create index syntax The complete syntax of the create index command is: create [unique] [clustered | nonclustered] index index_name on [[database.]owner.]table_name (column_name [, column_name]...) [with {{fillfactor | max_rows_per_page} = x, ignore_dup_key, sorted_data, [ignore_dup_row | allow_dup_row]}] [on segment_name] [with consumers = x] The following sections explain the various options to this command. Note The on segment _name extension to create index allows you to place your index on a segment that points to a specific database device or a collection of database devices. Before creating an index on a segment, see a System Administrator or the Database Owner for a list of segments that you can use. Certain segments may already be allocated to specific tables or indexes for performance reasons or for other considerations. Indexing more than one column: Composite indexes You have to specify two or more column names to create a composite index on the combined values in all the specified columns. Use composite indexes when two or more columns are best searched as a unit, for example, the first and last names of authors in the authors table. List the columns to be included in the composite index in sort-priority order, inside the parentheses after the table name, like this: create index auth_name_ind on authors(au_fname, au_lname) The columns in a composite index do not have to be in the same order as the columns in the create table statement. For example, the order of au_lname and au_fname could be reversed in the preceding index creation statement. You can specify up to 31 columns in a single composite index in Adaptive Server 11.9.2 and later. All the columns in a composite index must be in the same table. The maximum allowable size of the combined index values is 600 bytes. That is, the sum of the lengths of the columns that make up the composite index cannot exceed 600. Creating indexes 420 Adaptive Server Enterprise Using the unique option A unique index permits no two rows to have the same index value, including NULL. The system checks for duplicate values when the index is created, if data already exists, and checks each time data is added or modified with an insert or update. Specifying a unique index makes sense only when uniqueness is a characteristic of the data itself. For example, you would not want a unique index on a last_name column because there is likely to be more than one “Smith” or “Wong” in tables of even a few hundred rows. On the other hand, a unique index on a column holding social security numbers is a good idea. Uniqueness is a characteristic of the data—each person has a different social security number. Furthermore, a unique index serves as an integrity check. For instance, a duplicate social security number probably reflects some kind of error in data entry or on the part of the government. If you try to create a unique index on data that includes duplicate values, the command is aborted, and Adaptive Server displays an error message that gives the first duplicate. You cannot create a unique index on a column that contains null values in more than one row; these are treated as duplicate values for indexing purposes. If you try to change data on which there is a unique index, the results depend on whether you have used the ignore_dup_key option. See “Using the ignore_dup_key option” on page 426 for more information. You can use the unique keyword on composite indexes. Including IDENTITY columns in nonunique indexes The identity in nonunique index database option automatically includes an IDENTITY column in a table’s index keys so that all indexes created on the table are unique. This option makes logically nonunique indexes internally unique and allows them to process updatable cursors and isolation level 0 reads. To enable identity in nonunique indexes, enter: sp_dboption pubs2, "identity in nonunique index", trueCHAPTER 12 Creating Indexes on Tables Transact-SQL User’s Guide 421 The table must already have an IDENTITY column for the identity in nonunique index database option to work, either from a create table statement or by setting the auto identity database option to true before creating the table. Use identity in nonunique index if you plan to use cursors and isolation level 0 reads on tables with nonunique indexes. A unique index ensures that the cursor is positioned at the correct row the next time a fetch is performed on that cursor. For example, after setting identity in nonunique index and auto identity to true, suppose you create the following table, which has no indexes: create table title_prices (title varchar(80) not null, price money null) sp_help shows that the table contains an IDENTITY column, SYB_IDENTITY_COL, which is automatically created by the auto identity database option. If you create an index on the title column, use sp_helpindex to verify that the index automatically includes the IDENTITY column. Ascending and descending index-column values You can use the asc (ascending) and desc (descending) keywords to assign a sort order to each column in an index. By default, sort order is ascending. Creating indexes so that columns are in the same order specified in the order by clauses of queries eliminates sorting the columns during query processing. The following example creates an index on the Orders table. The index has two columns, the first is customer_ID, in ascending order, the second is date, in descending order, so that the most recent orders are listed first: create index nonclustered cust_order_date on Orders (customer_ID asc, date desc)Creating indexes 422 Adaptive Server Enterprise Using fillfactor, max_rows_per_page, and reservepagegap fillfactor, max_rows_per_page, and reservepagegap are space-management properties that apply to tables and indexes and affect the way physical pages are filled with data. For a detailed discussion of setting spacemanagement properties for indexes, see create index in the Reference Manual. Table 11-1 summarizes information about the space-management properties for indexes. Table 12-1: Summary of space-management properties for indexes Property Description Use Comments fillfactor Specifies the percent of space on a page that can be filled when the index is created. A fillfactor under 100% leaves space for inserts into a page without immediately causing page splits. Benefits: • Initially, fewer page splits. • Reduced contention for pages, because there are more pages and fewer rows on a page. Applies only to a clustered index on a data-only-locked table The fillfactor percentage is used only when an index is created on a table with existing data. It does not apply to pages and inserts after a table is created. If no fillfactor is specified, the systemwide default fillfactor is used. Initially, this is set to 100%, but can be changed using sp_configure. max_rows_per_page Specifies the maximum number of rows allowed per page. Benefit: • Can reduce contention for pages by limiting the number of rows per page and increasing the number of pages. Applies only to allpages-locked tables. The maximum value that you can set this property to is 256. max_rows_per_page applies at all times, from the creation of an index, onward. If not specified, the default is as many rows as will fit on a page. reservepagegap Determines the number of pages left empty when extents are allocated. For example, a reservepagegap of 16 means that 1 page of the 16 pages in 2 extents is left empty when the extents are allocated. Benefits: • Can reduce row forwarding and lessen the frequency of maintenance activities such as running reorg rebuild and recreating indexes. Applies to pages in all locking schemes. If reservepagegap is not specified, no pages are left empty when extents are allocated.CHAPTER 12 Creating Indexes on Tables Transact-SQL User’s Guide 423 This statement sets the fillfactor for an index to 65% and sets the reservepagegap to one empty page for each extent allocated: create index postalcode_ind2 on authors (postalcode) with fillfactor = 10, reservepagegap = 8 Using clustered or nonclustered indexes With a clustered index, Adaptive Server sorts rows on an ongoing basis so that their physical order is the same as their logical (indexed) order. The bottom or leaf level of a clustered index contains the actual data pages of the table. Create the clustered index before creating any nonclustered indexes, since nonclustered indexes are automatically rebuilt when a clustered index is created. There can be only one clustered index per table. It is often created on the primary key—the column or columns that uniquely identify the row. Logically, the database’s design determines a primary key. You can specify primary key constraints with the create table or alter table statements to create an index and enforce the primary key attributes for table columns. You can display information about constraints with sp_helpconstraint. Also, you can explicitly define primary keys, foreign keys, and common keys (pairs of keys that are frequently joined) by using sp_primarykey, sp_foreignkey, and sp_commonkey. However, these procedures do not enforce the key relationships. You can display information about defined keys with sp_helpkey and about columns that are likely join candidates with sp_helpjoins. For a definition of primary and foreign keys, see Chapter 17, “Triggers: Enforcing Referential Integrity.” For complete information on system procedures, see the Reference Manual. With a nonclustered index, the physical order of the rows is not the same as their indexed order. The leaf level of a nonclustered index contains pointers to rows on data pages. More precisely, each leaf page contains an indexed value and a pointer to the row with that value. In other words, a nonclustered index has an extra level between the index structure and the data itself. Using clustered or nonclustered indexes 424 Adaptive Server Enterprise Each of the up to 249 nonclustered indexes permitted on a table can provide access to the data in a different sorted order. Finding data using a clustered index is almost always faster than using a nonclustered index. In addition, a clustered index is advantageous when many rows with contiguous key values are being retrieved—that is, on columns that are often searched for ranges of values. Once the row with the first key value is found, rows with subsequent indexed values are guaranteed to be physically adjacent, and no further searches are necessary. If neither the clustered nor the nonclustered keyword is used, Adaptive Server creates a nonclustered index. Here is how the titleidind index on the title_id column of the titles table is created. If you want to try this command, you must first drop the index: drop index titles.titleidind Then, create the clustered index: create clustered index titleidind on titles(title_id) If you think you will often want to sort the people in the friends_etc table, which you created in Chapter 8, “Creating Databases and Tables,” by postal code, create a nonclustered index on the postalcode column: create nonclustered index postalcodeind on friends_etc(postalcode) A unique index does not make sense here, since some of your contacts are likely to have the same postal code. A clustered index would not be appropriate either, since the postal code is not the primary key. The clustered index in friends_etc should be a composite index on the personal name and surname columns, for example: create clustered index nmind on friends_etc(pname, sname) CHAPTER 12 Creating Indexes on Tables Transact-SQL User’s Guide 425 Creating clustered indexes on segments The create index command allows you to create the index on a specified segment. Since the leaf level of a clustered index and its data pages are the same by definition, creating a clustered index and using the on segment_name extension moves a table from the device on which it was created to the named segment. See a System Administrator or the Database Owner before creating tables or indexes on segments; certain segments may be reserved for performance reasons. Creating clustered indexes on partitioned tables You can create a clustered index on a partitioned table if all of the following conditions are true: • The server is configured to run in parallel, • The select into/bulkcopy/pllsort database option is set to true, and • As many worker threads are available as the number of partitions. However, to speed recovery, dump the database after creating the clustered index. For more information about partitioned tables and creating clustered indexes on them, see the System Administration Guide. See a System Administrator or the Database Owner before creating a clustered index on a partitioned table. Specifying index options The index options ignore_dup_key, ignore_dup_row, and allow_dup_row control what happens when a duplicate key or duplicate row is created with insert or update. Table 12-2 shows which option to use, based on the type of index.Specifying index options 426 Adaptive Server Enterprise Table 12-2: Index options Using the ignore_dup_key option If you try to insert a duplicate value into a column that has a unique index, the command is canceled. You can avoid this situation by including the ignore_dup_key option with a unique index. The unique index can be either clustered or nonclustered. When you begin data entry, any attempt to insert a duplicate key is canceled with an error message. After the cancellation, any transaction that was active at the time may continue as though the update or insert had never taken place. Nonduplicate keys are inserted normally. You cannot create a unique index on a column that already includes duplicate values, whether or not ignore_dup_key is set. If you attempt to do so, Adaptive Server prints an error message and a list of the duplicate values. You must eliminate duplicates before you create a unique index on the column. Here is an example of using the ignore_dup_key option: create unique clustered index phone_ind on friends_etc(phone) with ignore_dup_key Using the ignore_dup_row and allow_dup_row options ignore_dup_row and allow_dup_row are options for creating a nonunique, clustered index. These options are not relevant when creating a nonunique, nonclustered index. Since an Adaptive Server nonclustered index attaches a unique row identification number internally, it never worries about duplicate rows—even for identical data values. ignore_dup_row and allow_dup_row are mutually exclusive. Index type Options Clustered ignore_dup_row | allow_dup_row Unique clustered ignore_dup_key Nonclustered None Unique nonclustered ignore_dup_key Unique nonclustered ignore_dup_rowCHAPTER 12 Creating Indexes on Tables Transact-SQL User’s Guide 427 A nonunique clustered index allows duplicate keys, but does not allow duplicate rows unless you specify allow_dup_row. If allow_dup_row is set, you can create a new nonunique, clustered index on a table that includes duplicate rows, and you can subsequently insert or update duplicate rows. If any index in the table is unique, the requirement for uniqueness—the most stringent requirement—takes precedence over the allow_dup_row option. Thus, allow_dup_row applies only to tables with nonunique indexes. You cannot use this option if a unique clustered index exists on any column in the table. The ignore_dup_row option eliminates duplicates from a batch of data. When you enter a duplicate row, Adaptive Server ignores that row and cancels that particular insert or update with an informational error message. After the cancellation, any transaction that may have been active at the time continues as though the insert or update had never taken place. Non-duplicate rows are inserted normally. The ignore_dup_row applies only to tables with nonunique indexes: you cannot use this keyword if a unique index exists on any column in the table. Table 12-3 illustrates how allow_dup_row and ignore_dup_row affect attempts to create a nonunique, clustered index on a table that includes duplicate rows, and to enter duplicate rows into a table. Table 12-3: Duplicate row options in indexes Using the sorted_data option The sorted_data option of create index speeds creation of an index when the data in the table is already in sorted order, for example, when you have used bcp to copy data that has already been sorted into an empty table. The speed increase becomes significant on large tables and increases to several times faster in tables larger than 1GB. Option Has duplicates Enter duplicates Neither option set create index command fails. Command fails. allow_dup_row set Command completes. Command completes. ignore_dup_row set Index created but duplicate rows deleted; error message. Duplicates not inserted/updated; error message; transaction completes.Dropping indexes 428 Adaptive Server Enterprise If sorted_data is specified but data is not in sorted order, an error message displays and the command is aborted. This option speeds indexing only for clustered indexes or unique nonclustered indexes. Creating a nonunique nonclustered index will, however, be successful unless there are rows with duplicate keys. If there are rows with duplicate keys, an error message displays and the command is aborted. Certain other create index options require a sort even if sorted_data is specified. See the create index description in the Reference Manual. Using the on segment_name option The on segment_name clause specifies a database segment name on which the index is to be created. A nonclustered index can be created on a different segment than the data pages. For example: create index titleind on titles(title) on seg1 If you use segment_name when creating a clustered index, the table containing the index moves to the segment you specify. See a System Administrator or the Database Owner before creating tables or indexes on segments; certain segments may be reserved for performance reasons. Dropping indexes The drop index command removes an index from the database. Its syntax is: drop index table_name.index_name [, table_name.index_name]... When you use this command, Adaptive Server removes the specified indexes from the database, reclaiming their storage space. Only the owner of the index can drop it. drop index permission cannot be transferred to other users. The drop index command cannot be used on any of the system tables in the master database or in the user database. CHAPTER 12 Creating Indexes on Tables Transact-SQL User’s Guide 429 You might want to drop an index if it is not used for most or all of your queries. To drop the index phone_ind in the friends_etc table, the command is: drop index friends_etc.phone_ind Determining what indexes exist on a table To see the indexes that exist on a table, you can use sp_helpindex. Here is a report on the friends_etc table: sp_helpindex friends_etc index_name index_description index_keys index_max_rows_per_page ------------- ---------------------------- ------------- ----------------------- nmind clustered located on default pname, sname 0 postalcodeind nonclustered located on default postalcode 0 (2 rows affected, return status = 0) sp_help runs sp_helpindex at the end of its report. sp_statistics returns a list of indexes on a table. For example: sp_statistics friends_etc table_qualifier table_owner table_name non_unique index_qualifier index_name type seq_in_index column_name collation cardinality pages -------------------------------- ------------------ -------------- -------------------------------- ---------- -------------------------------- ---------- --------------------- ------ ------------ ----------------------- --------- --------- ----------- ----------- pubs2 dbo friends_etc NULLDetermining what indexes exist on a table 430 Adaptive Server Enterprise NULL NULL 0 NULL NULL NULL 0 1 pubs2 dbo friends_etc 1 friends_etc nmind 1 1 pname A 0 1 pubs2 dbo friends_etc 1 friends_etc nmind 1 2 sname A 0 1 pubs2 dbo friends_etc 1 friends_etc postalcodeind 3 1 postalcode A NULL NULL (4 rows affected, return status = 0) In addition, if you follow the table name with “1”, sp_spaceused reports the amount of space used by a table and its indexes. For example: sp_spaceused friends_etc, 1 index_name size reserved unused -------------------- ---------- ---------- ---------- nmind 2 KB 32 KB 28 KB postalcodeind 2 KB 16 KB 14 KB name rowtotal reserved data index_size unused ------------ ---------- ------------ ------- --------------- -------- friends_etc 1 48 KB 2 KB 4 KB 42 KB (return status = 0)CHAPTER 12 Creating Indexes on Tables Transact-SQL User’s Guide 431 Updating statistics about indexes The update statistics command helps Adaptive Server make the best decisions about which indexes to use when it processes a query, by keeping it up to date about the distribution of the key values in the indexes. Use update statistics when a large amount of data in an indexed column has been added, changed, or deleted. When Component Integration Services is enabled, update statistics can generate accurate distribution statistics for remote tables. For more information, see the Component Integration Services User’s Guide. Permission to issue the update statistics command defaults to the table owner and is not transferable. Its syntax is: update statistics table_name [index_name] If you do not specify an index name, the command updates the distribution statistics for all the indexes in the specified table. Giving an index name updates statistics for that index only. You can find the names of indexes by using sp_helpindex. Here is how to list the indexes for the authors table: sp_helpindex authors index_name index_description index_keys index_max_rows_per_page ---------- ----------------- ---------- ----------------------- auidind clustered, unique au_id 0 aunmind nonclustered au_lname, 0 au_fname (2 rows affected, return status = 0) To update the statistics for all of the indexes, type: update statistics authors To update the statistics only for the index on the au_id column, type: update statistics authors auidind Because Transact-SQL does not require index names to be unique in a database, you must give the name of the table with which the index is associated. Adaptive Server runs update statistics automatically when you create an index on existing data. Updating statistics about indexes 432 Adaptive Server Enterprise Updating partition statistics Like the update statistics command for unpartitioned tables, the update partition statistics command helps Adaptive Server make the best decisions when it processes a query, by keeping it up to date about the number of pages within the partitions. Use update partition statistics when a large amount of data in a partitioned table has been added, changed, or deleted. Permission to issue the update partiton statistics command defaults to the table owner and is not transferable. Its syntax is: update partition statistics table_name For example, suppose the authors table was partitioned as follows: alter table authors partition 3 Then you run sp_helpartition to see how the partitions were distributed: sp_helpartition authors partitionid firstpage controlpage ptn_data_pages ----------- ----------- ----------- -------------- 1 553 554 1 2 817 816 1 3 1009 1008 1 (3 rows affected, return status = 0) Afterwards, you update the statistics for authors as follows: update partition statistics authors Using sp_helpartition on authors shows the following update: partitionid firstpage controlpage ptn_data_pages ----------- ----------- ----------- -------------- 1 553 554 10 2 817 816 1 3 1009 1008 1 (3 rows affected, return status = 0) Dropping and re-creating a clustered index automatically redistributes the data within partitions and updates the partition statistics.Transact-SQL User’s Guide 433 C H A P T E R 1 3 Defining Defaults and Rules for Data A default is a value that Adaptive Server inserts into a column if the user does not explicitly enter a value for that column. In database management, a rule specifies what you are or are not allowed to enter in a particular column or in any column with a given user-defined datatype. You can use defaults and rules to help maintain the integrity of data across the database. This chapter discusses: How defaults and rules work You can define a value for a table column or user-defined datatype that will be automatically inserted if a user does not explicitly enter a value. For example, you can create a default that has the value “???” or the value “fill in later.” You can also define rules for that table column or datatype to restrict the types of values users can enter for it. In a relational database management system, every data element must contain some value, even if that value is null. As discussed in Chapter 8, “Creating Databases and Tables,” some columns do not accept the null value. For those columns, some other value must be entered, either a value explicitly entered by the user or a default entered by Adaptive Server. Topic Page How defaults and rules work 433 Creating defaults 434 Dropping defaults 440 Creating rules 440 Dropping rules 445 Getting information about defaults and rules 445Creating defaults 434 Adaptive Server Enterprise Rules enforce the integrity of data in ways not covered by a column’s datatype. A rule can be connected to a specific column, to several specific columns or to a specified, user-defined datatype. Every time a user enters a value, Adaptive Server checks it against the most recent rule that has been bound to the specified column. Data entered prior to the creation and binding of a rule is not checked. As an alternative to using defaults and rules, you can use the default clause and the check integrity constraint of the create table statement to accomplish some of the same tasks. However, they are specific for that table and cannot be bound to columns of other tables or to user-defined datatypes. For more information about integrity constraints, see Chapter 8, “Creating Databases and Tables.” Creating defaults You can create or drop defaults at any time, before or after data has been entered in a table. In general, to create defaults you: 1 Define the default, using create default. 2 Bind the default to the appropriate table column or user-defined datatype using sp_bindefault. 3 Test the bound default by inserting data. You can drop defaults using drop default and remove their association using sp_unbinddefault. When you create and bind defaults: • Make sure the column is large enough for the default. For example, a char (2) column will not hold a 17-byte string like “Nobody knows yet.” • Be careful when you put a default on a user-defined datatype and a different default on an individual column of that type. If you bind the datatype default first and then the column default, the column default replaces the user-defined datatype default for the named column only. The user-defined datatype default is bound to all the other columns having that datatype. However, once you bind another default to a column that has a default because of its type, that column ceases to be influenced by defaults bound to its datatype. This issue is discussed in more detail under “Binding defaults” on page 436. CHAPTER 13 Defining Defaults and Rules for Data Transact-SQL User’s Guide 435 • Watch for conflicts between defaults and rules. Be sure the default value is allowed by the rule; otherwise, the default may be eliminated by the rule. For example, if a rule allows entries between 1 and 100, and the default is set to 0, the rule rejects the default entry. Either change the default or change the rule. create default syntax The syntax of create default is: create default [owner.]default_name as constant_expression Default names must follow the rules for identifiers. You can create a default in the current database only. Within a database, default names must be unique for each user. For example, you cannot create two defaults called phonedflt. However, as “guest,” you can create a phonedflt even if dbo.phonedflt already exists because the owner names make each one distinct. Another example: suppose you want to create a default value of “Oakland” that can be used with the city column of friends_etc and possibly with other columns or user datatypes. To create the default, enter: create default citydflt as "Oakland" As you continue to follow this example, you can use any city name that works for the people you are going to enter in your personal table. Enclose character and date constants in quotes; money, integer, and floating point constants do not require them. Binary data must be preceded by “0x”, and money data should be preceded by a dollar sign ($). The default value must be compatible with the datatype of the column. You cannot use “none,” for example, as a default for a numeric column, but 0 is appropriate. If you specify NOT NULL when you create a column and do not associate a default with it, Adaptive Server produces an error message whenever anyone fails to make an entry in that column. Creating defaults 436 Adaptive Server Enterprise Usually, you will enter default values when you create a table. However, during a session in which you want to enter many rows having the same values in one or more columns, it may be convenient to create a default tailored to that session before you begin. Note You cannot issue create table with a declarative default and then insert data into the table in the same batch or procedure. Either separate the create and insert statements into two different batches or procedures, or use execute to perform the actions separately. Binding defaults After you have created a default, use sp_bindefault to bind the default to a column or user-defined datatype. For example, suppose you create the following default: create default advancedflt as "UNKNOWN" Now, bind the default to the appropriate column or user-defined datatype with sp_bindefault. sp_bindefault advancedflt, "titles.advance" The default takes effect only if the user does not add an entry to the advance column of the titles table. Not making an entry is different than entering a null value. A default can connect to a particular column, to a number of columns, or to all columns in the database that have a given user-defined datatype. Note To get the default, you must issue an insert or update command with a column list that does not include the column that has the default. The following restrictions apply to defaults: • The default applies to new rows only. It does not retroactively change existing rows. Defaults take effect only when no entry is made. If you supply any value for the column, including NULL, the default has no effect. • You cannot bind a default to a system datatype. • You cannot bind a default to a timestamp column, because Adaptive Server generates values for timestamp columns. CHAPTER 13 Defining Defaults and Rules for Data Transact-SQL User’s Guide 437 • You cannot bind defaults to system tables. • You can bind a default to an IDENTITY column or to a user-defined datatype with the IDENTITY property, but Adaptive Server ignores such defaults. When you insert a row into a table without specifying a value for the IDENTITY column, Adaptive Server assigns a value that is 1 greater than the last value assigned. • If a default already exists on a column, you must remove it before binding a new default. Use sp_unbindefault to remove defaults created with sp_bindefault. Use alter table to remove defaults created with create table. To bind citydflt to the city column in friends_etc, type: sp_bindefault citydflt, "friends_etc.city" Notice that the table and column name are enclosed in quotes, because of the embedded punctuation (the period). If you create a special datatype for all city columns in every table in your database, and bind citydflt to that datatype, “Oakland” appears only where city names are appropriate. For example, if the user datatype is called citytype, here is how to bind citydflt to it: sp_bindefault citydflt, citytype To prevent existing columns or a specific user datatype from inheriting the new default, use the futureonly parameter when binding a default to a user datatype. However, do not use futureonly when binding a default to a column. Here is how you create and bind the new default “Berkeley” to the datatype citytype for use by new table columns only: create default newcitydflt as "Berkeley" sp_bindefault newcitydflt, citytype, futureonly “Oakland” continues to appear as the default for any existing table columns using citytype. If most of the people in your table live in the same zip code area, you can create a default to save data entry time. Here is one, along with its binding, that is appropriate for a section of Oakland: create default zipdflt as "94609" sp_bindefault zipdflt, "friends_etc.postalcode" Here is the complete syntax for sp_bindefault: sp_bindefault defname, objname [, futureonly] Creating defaults 438 Adaptive Server Enterprise defname is the name of the default created with create default. objname is the name of the table and column, or of the user-defined datatype, to which the default is to be bound. If the parameter is not of the form table.column, it is assumed to be a user-defined datatype. All columns of a specified user-defined datatype become associated with the specified default unless you use the optional futureonly parameter, which prevents existing columns of that user datatype from inheriting the default. Note Defaults cannot be bound to columns and used during the same batch. sp_bindefault cannot be in the same batch as insert statements that invoke the default. Unbinding defaults Unbinding a default means disconnecting it from a particular column or userdefined datatype. An unbound default is still stored in the database and is available for future use. Use sp_unbindefault to remove the binding between a default and a column or datatype. Here is how you unbind the current default from the city column of the friends_etc table: execute sp_unbindefault "friends_etc.city" To unbind a default from the user-defined datatype citytype, use: sp_unbindefault citytype The complete syntax of sp_unbindefault is: sp_unbindefault objname [, futureonly] If the objname parameter you give is not of the form table.column, Adaptive Server assumes it is a user-defined datatype. When you unbind a default from a user-defined datatype, the default is unbound from all columns of that type unless you give the optional futureonly parameter, which prevents existing columns of that datatype from losing their binding with the default.CHAPTER 13 Defining Defaults and Rules for Data Transact-SQL User’s Guide 439 How defaults affect NULL values If you specify NOT NULL when you create a column and do not create a default for it, Adaptive Server produces an error message whenever anyone inserts a row and fails to make an entry in that column. When you drop a default for a NULL column, Adaptive Server inserts NULL in that position each time you add rows without entering any value for that column. When you drop a default for a NOT NULL column, you get an error message when rows are added, without a value entered for that column. Table 13-1 illustrates the relationship between the existence of a default and the definition of a column as NULL or NOT NULL. Table 13-1: Column definition and null defaults After creating a default After you create a default, the source text describing the default is stored in the text column of the syscomments system table. Do not remove this information; doing so may cause problems for future versions of Adaptive Server. Instead, encrypt the text in syscomments by using sp_hidetext, described in the Reference Manual. For more information, see “Compiled objects” on page 4. Column definition User entry Result Null and default defined No value NULL value Default used NULL used Null defined, no default defined No value NULL value NULL used NULL used Not null, default defined No value NULL value Default used Error Not null, no default defined No value NULL value Error ErrorDropping defaults 440 Adaptive Server Enterprise Dropping defaults To remove a default from the database entirely, use the drop default command. Unbind the default from all columns and user datatypes before you drop it. (See “Unbinding defaults” on page 438.) If you try to drop a default that is still bound, Adaptive Server displays an error message and the drop default command fails. Here is how to remove citydflt. First, you unbind it: sp_unbindefault citydft Then you can drop citydft: drop default citydflt The complete syntax of drop default is: drop default [owner.]default_name [, [owner.]default_name] ... A default can be dropped only by its owner. For more information about unbinding a default see sp_unbindefault and alter table in the Reference Manual. Creating rules A rule lets you specify what users can or cannot enter into a particular column or any column with a user-defined datatype. In general, to create a rule you: 1 Create the rule using create rule. 2 Bind the rule to a column or user-defined datatype using sp_bindrule. 3 Test the bound rule by inserting data. Many errors in creating and binding rules can be caught only by testing with an insert or update command. You can unbind a rule from the column or datatype either by using sp_unbindrule or by binding a new rule to the column or datatype. create rule syntax The syntax of create rule is: create rule [owner.]rule_name as condition_expressionCHAPTER 13 Defining Defaults and Rules for Data Transact-SQL User’s Guide 441 Rule names must follow the rules for identifiers. You can create a rule in the current database only. Within a database, rule names must be unique for each user. For example, a user cannot create two rules called socsecrule. However, two different users can create a rule named socsecrule, because the owner names make each one distinct. Here is how the rule permitting five different pub_id numbers and one dummy value (99 followed by any two digits) was created: create rule pub_idrule as @pub_id in ("1389", "0736", "0877", "1622", "1756") or @pub_id like "99[0-9][0-9]" The as clause contains the name of the rule’s argument, prefixed with “@”, and the definition of the rule itself. The argument refers to the column value that is affected by the update or insert statement. In the preceding example, the argument is @pub_id, a convenient name, since this rule is to be bound to the pub_id column. You can use any name for the argument, but the first character must be “@.” Using the name of the column or datatype to which the rule will be bound can help you remember what it is for. The rule definition can contain any expression that is valid in a where clause, and can include arithmetic operators, comparison operators, like, in, between, and so on. However, the rule definition cannot reference any column or other database object directly. Built-in functions that do not reference database objects can be included. The following example creates a rule that forces the values you enter to comply with a particular “picture.” In this case, each value entered in the column must begin with “415” and be followed by 7 more characters: create rule phonerule as @phone like "415____ _ _ _" To make sure that the ages you enter for your friends are between 1 and 120, but never 17, try this: create rule agerule as @age between 1 and 120 and @age ! = 17Creating rules 442 Adaptive Server Enterprise Binding rules After you have created a rule, use sp_bindrule to link the rule to a column or user-defined datatype. Here is the complete syntax for sp_bindrule: sp_bindrule rulename, objname [, futureonly] The rulename is the name of the rule created with create rule. The objname is the name of the table and column, or of the user-defined datatype to which the rule is to be bound. If the parameter is not of the form table.column, it is assumed to be a user datatype. Use the optional futureonly parameter only when binding a rule to a userdefined datatype. All columns of a specified user-defined datatype become associated with the specified rule unless you specify futureonly, which prevents existing columns of that user datatype from inheriting the rule. If the rule associated with a given user-defined datatype has previously been changed, Adaptive Server maintains the changed rule for existing columns of that userdefined datatype. The following restrictions apply to rules: • You cannot bind a rule to a text, image, or timestamp datatype column. • Adaptive Server does not allow rules on system tables. Rules bound to columns You bind a rule to a column by using sp_bindrule with the rule name and the quoted table name and column name. This is how pub_idrule was bound to publishers.pub_id: sp_bindrule pub_idrule, "publishers.pub_id" Here is a rule to ensure that all the postal codes entered will have 946 as the first 3 digits: create rule postalcoderule946 as @postalcode like "946[0-9][0-9]" Bind it to the postalcode column in friends_etc like this: sp_bindrule postalcoderule946, "friends_etc.postalcode" Rules cannot be bound to columns and used during the same batch. sp_bindrule cannot be in the same batch as insert statements that invoke the rule. CHAPTER 13 Defining Defaults and Rules for Data Transact-SQL User’s Guide 443 Rules bound to user-defined datatypes You cannot bind a rule to a system datatype, but you can bind one to a userdefined datatype. To bind phonerule to a user-defined datatype called p#, enter: sp_bindrule phonerule, "p#" Precedence of rules Rules bound to columns always take precedence over rules bound to user datatypes. Binding a rule to a column replaces a rule bound to the user datatype of that column, but binding a rule to a datatype does not replace a rule bound to a column of that user datatype. A rule bound to a user-defined datatype is activated only when you attempt to insert a value into, or update, a database column of the user-defined datatype. Because rules do not test variables, do not assign a value to a user-defined datatype variable that would be rejected by a rule bound to a column of the same datatype. Table 12-2 indicates the precedence when binding rules to columns and user datatypes where rules already exist: Table 13-2: Precedence of rules When you are entering data that requires special temporary constraints on some columns, you can create a new rule to help check the data. For example, suppose that you are adding data to the debt column of the friends_etc table. You know that all the debts you want to record today are between $5 and $200. To avoid accidentally typing an amount outside those limits, create a rule like this one: create rule debtrule as @debt = $0.00 or @debt between $5.00 and $200.00 The @debt rule definition allows for an entry of $0.00 to maintain the default previously defined for this column. Bind debtrule to the debt column like this: sp_bindrule debtrule, "friends_etc.debt" New rule bound to Old rule bound to User Datatype Column User Datatype Replaces old rule No change Column Replaces old rule Replaces old ruleCreating rules 444 Adaptive Server Enterprise Rules and NULL values You cannot define a column to allow nulls, and then override this definition with a rule that prohibits null values. For example, if a column definition specifies NULL and the rule specifies the following, an implicit or explicit NULL does not violate the rule: @val in (1,2,3) The column definition overrides the rule, even a rule that specifies: @val is not null After defining a rule After you define a rule, the source text describing the rule is stored in the text column of the syscomments system table. Do not remove this information; doing so may cause problems for future versions of Adaptive Server. Instead, encrypt the text in syscomments by using sp_hidetext, described in the Reference Manual. For more information, see “Compiled objects” on page 4. Unbinding rules Unbinding a rule disconnects it from a particular column or user-defined datatype. An unbound rule’s definition is still stored in the database and is available for future use. There are two ways to unbind a rule: • Use sp_unbindrule to remove the binding between a rule and a column or user-defined datatype. • Use sp_bindrule to bind a new rule to that column or datatype. The old one is automatically unbound. Here is how to disassociate debtrule (or any other currently bound rule) from friends_etc.debt: sp_unbindrule "friends_etc.debt" The rule is still in the database, but it has no connection to friends_etc.debt. To unbind a rule from the user-defined datatype p#, use: sp_unbindrule "p#" The complete syntax of sp_unbindrule is: CHAPTER 13 Defining Defaults and Rules for Data Transact-SQL User’s Guide 445 sp_unbindrule objname [, futureonly] If the objname parameter you use is not of the form “table.column”, Adaptive Server assumes it is a user-defined datatype. When you unbind a rule from a user-defined datatype, the rule is unbound from all columns of that type unless: • You give the optional futureonly parameter, which prevents existing columns of that datatype from losing their binding with the rule, or • The rule on a column of that user-defined datatype has been changed so that its current value is different from the rule being unbound. Dropping rules To remove a rule from the database entirely, use the drop rule command. Unbind the rule from all columns and user datatypes before you drop it. If you try to drop a rule that is still bound, Adaptive Server displays an error message, and drop rule fails. However, you need not unbind and then drop a rule to bind a new one. Simply bind a new one in its place. To remove phonerule after unbinding it: drop rule phonerule The complete syntax for drop rule is: drop rule [owner.]rule_name [, [owner.]rule_name] ... After you drop a rule, new data entered into the columns that previously were governed by it goes in without these constraints. Existing data is not affected in any way. A rule can be dropped only by its owner. Getting information about defaults and rules The system procedure sp_help, when used with a table name, displays the rules and defaults that are bound to columns. This example displays information about the authors table in the pubs2 database, including the rules and defaults: sp_help authors Getting information about defaults and rules 446 Adaptive Server Enterprise sp_help also reports on a rule bound to a user-defined datatype. To check whether a rule is bound to the user-defined datatype p#, use: sp_help "p#" sp_helptext reports the definition (the create statement) of a rule or default. If the source text of a default or rule was encrypted using sp_hidetext, Adaptive Server displays a message advising you that the text is hidden. For information about hiding source text, see sp_hidetext in the Reference Manual. If the System Security Officer has reset the allow select on syscomments.text column parameter with sp_configure (as required to run Adaptive Server in the evaluated configuration), you must be the creator of the default or rule or a System Administrator to view the text of a default or rule through sp_helptext. For more information, see evaluated configuration in the Adaptive Server Glossary.Transact-SQL User’s Guide 447 C H A P T E R 1 4 Using Batches and Control-ofFlow Language Transact-SQL allows you to group a series of statements as a batch, either interactively or from an operating system file. You can also use TransactSQL’s control-of-flow language to connect the statements, using programming constructs. A variable is an entity that is assigned a value. This value can change during the batch or stored procedure in which the variable is used. Adaptive Server has two kinds of variables: local and global. Local variables are user-defined, whereas global variables are supplied by the system and are predefined. This chapter discusses: Introduction Up to this point, each example in the Transact-SQL User’s Guide has consisted of an individual statement. You submit statements to Adaptive Server one at a time, entering the statement and receiving results interactively. Adaptive Server can also process multiple statements submitted as a batch, either interactively or from a file. A batch or batch file is a set of Transact-SQL statements that are submitted together and executed as a group, one after the other. A batch is terminated by an end-of-batch signal. With the isql utility, this is the word “go” on a line by itself. For details on isql, see the Utility Programs manual for your platform. Topic Page Introduction 447 Rules associated with batches 448 Using control-of-flow language 453 Local variables 478 Global variables 483Rules associated with batches 448 Adaptive Server Enterprise Here is an example of a batch that contains two Transact-SQL statements: select count(*) from titles select count(*) from authors go Technically, a single Transact-SQL statement can constitute a batch, but it is more common to think of a batch as containing multiple statements. Frequently, a batch of statements is written to an operating system file before being submitted to isql. Transact-SQL provides special keywords called control-of-flow language that allow the user to control the flow of execution of statements. Control-of-flow language can be used in single statements, in batches, in stored procedures, and in triggers. Without control-of-flow language, separate Transact-SQL statements are performed sequentially, as they occur. Correlated subqueries, discussed in Chapter 4, “Subqueries: Using Queries Within Other Queries,” are a partial exception. Control-of-flow language permits statements to connect and to relate to each other using programming-like constructs. Control-of-flow language, such as if...else for conditional performance of commands and while for repetitive execution, lets you refine and control the operation of Transact-SQL statements. The Transact-SQL control-of-flow language transforms standard SQL into a very high-level programming language. Rules associated with batches There are rules governing which Transact-SQL statements can be combined into a single batch. These batch rules are as follows: • Before referencing objects in a database, issue a use statement for that database. For example: use master go select count(*) from sysdatabases go • You cannot combine the following database commands with other statements in a batch:CHAPTER 14 Using Batches and Control-of-Flow Language Transact-SQL User’s Guide 449 • create procedure • create rule • create default • create trigger • You can combine the following database commands with other TransactSQL statements in a batch: • create database (except that you cannot create a database and create or access objects in the new database in a single batch) • create table • create index • create view • You cannot bind rules and defaults to columns and use them in the same batch. sp_bindrule and sp_bindefault cannot be in the same batch as insert statements that invoke the rule or default. • You cannot drop an object and then reference or re-create it in the same batch. • If a table already exists, you cannot re-create it in a batch, even if you include a test in the batch for the table’s existence. Adaptive Server compiles a batch before executing it. During compilation, Adaptive Server makes no permission checks on objects, such as tables and views, that are referenced by the batch. Permission checks occur when Adaptive Server executes the batch. An exception to this is when Adaptive Server accesses a database other than the current one. In this case, Adaptive Server displays an error message at compilation time without executing any statements in the batch. Assume that your batch contains these statements: select * from taba select * from tabb select * from tabc select * from tabd If you have the necessary permissions for all statements except the third one (select * from tabc), Adaptive Server returns an error message for that statement and returns results for all the others.Rules associated with batches 450 Adaptive Server Enterprise Examples of using batches The examples in this section illustrate batches using the format of the isql utility, which has a clear end-of-batch signal—the word “go” on a line by itself. Here is a batch that contains two select statements in a single batch: select count(*) from titles select count(*) from authors go ------------- 18 (1 row affected) ------------- 23 (1 row affected) You can create a table and reference it in the same batch. This batch creates a table, inserts a row into it, and then selects everything from it: create table test (column1 char(10), column2 int) insert test values ("hello", 598) select * from test go (1 row affected) column1 column2 ------- ------- hello 598 (1 row affected) You can combine a use statement with other statements, as long as the objects you reference in subsequent statements are in the database in which you started. This batch selects from a table in the master database and then opens the pubs2 database. The batch begins by making the master database current; afterwards, pubs2 is the current database. use master go select count(*) from sysdatabases use pubs2 go ------------- 6 CHAPTER 14 Using Batches and Control-of-Flow Language Transact-SQL User’s Guide 451 (1 row affected) You can combine a drop statement with other statements as long as you do not reference or re-create the dropped object in the same batch. This example combines a drop statement with a select statement: drop table test select count(*) from titles go ------------ 18 (1 row affected) If there is a syntax error anywhere in the batch, none of the statements is executed. For example, here is a batch with a typing error in the last statement, and the results: select count(*) from titles select count(*) from authors slect count(*) from publishers go Msg 156, Level 15, State 1: Line 3: Incorrect syntax near the keyword ’count’. Batches that violate a batch rule also generate error messages. Here are some examples of illegal batches: create table test (column1 char(10), column2 int) insert test values ("hello", 598) select * from test create procedure testproc as select column1 from test go Msg 111, Level 15, State 7: Line 6: CREATE PROCEDURE must be the first command in a query batch. create default phonedflt as "UNKNOWN" sp_bindefault phonedflt, "authors.phone" goRules associated with batches 452 Adaptive Server Enterprise Msg 102, Level 15, State 1: Procedure ’phonedflt’, Line 2: Incorrect syntax near ’sp_bindefault’. The next batch will work if you are already in the database you specify in the use statement. If you try it from another database such as master, however, you will get an error message. use pubs2 select * from titles go Msg 208, Level 16, State 1: Server ’hq’, Line 2: titles not found. Specify owner.objectname or use sp_help to check whether the object exists (sp_help may produce lots of output) drop table test create table test (column1 char(10), column2 int) go Msg 2714, Level 16, State 1: Server ’hq’, Line 2: There is already an object named ’test’ in the database. Batches submitted as files You can submit one or more batches of Transact-SQL statements to isql from an operating system file. A file can include more than one batch, that is, more than one collection of statements, each terminated by the word “go.” For example, an operating system file might contain the following three batches: use pubs2 go select count(*) from titles select count(*) from authors go create table hello (column1 char(10), column2 int) insert hello CHAPTER 14 Using Batches and Control-of-Flow Language Transact-SQL User’s Guide 453 values ("hello", 598) select * from hello go Here are the results of submitting this file to the isql utility: ------------- 18 (1 row affected) ------------- 23 (1 row affected) column1 column2 --------- --------- hello 598 (1 row affected) See isql in the Utility Guide for environment-specific information about running batches stored in files. Using control-of-flow language Use control-of-flow language with interactive statements, in batches, and in stored procedures. Table 14-1lists the control-of-flow and related keywords and their functions.Using control-of-flow language 454 Adaptive Server Enterprise Table 14-1: Control-of-flow and related keywords if...else The keyword if, with or without its companion else, introduces a condition that determines whether the next statement is executed. The Transact-SQL statement executes if the condition is satisfied, that is, if it returns TRUE. The else keyword introduces an alternate Transact-SQL statement that executes when the if condition returns FALSE. The syntax for if and else is: if boolean_expression statement [else [if boolean_expression] statement ] Keyword Function if Defines conditional execution. …else Defines alternate execution when the if condition is false. case Defines conditional expressions using when…then statements instead of if…else. begin Beginning of a statement block. …end End of a statement block. while Repeat performance of statements while condition is true. break Exit from the end of the next outermost while loop. …continue Restart while loop. declare Declare local variables. goto label Go to label:, a position in a statement block. return Exit unconditionally. waitfor Set delay for command execution. print Print a user-defined message or local variable on user’s screen. raiserror Print a user-defined message or local variable on user’s screen and set a system flag in the global variable @@error. /* comment */ or --comment Insert a comment anywhere in a Transact-SQL statement.CHAPTER 14 Using Batches and Control-of-Flow Language Transact-SQL User’s Guide 455 A Boolean expression returns TRUE or FALSE. It can include a column name, a constant, any combination of column names and constants connected by arithmetic or bitwise operators, or a subquery, as long as the subquery returns a single value. If the Boolean expression contains a select statement, the select statement must be enclosed in parentheses, and it must return a single value. Here is an example of using if alone: if exists (select postalcode from authors where postalcode = "94705") print "Berkeley author" If one or more of the zip codes in the authors table has the value “94705”, the message “Berkeley author” is printed. The select statement in this example returns a single value, either TRUE or FALSE, because it is used with the keyword exists. The exists keyword functions here just as it does in subqueries. See Chapter 4, “Subqueries: Using Queries Within Other Queries.” Here is an example, using both if and else, that tests for the presence of usercreated objects that have ID numbers greater than 50. If user objects exist, the else clause selects their names, types, and ID numbers. if (select max(id) from sysobjects) < 50 print "There are no user-created objects in this database." else select name, type, id from sysobjects where id > 50 and type = "U" (0 rows affected) name type id ------------ ---- --------- authors U 16003088 publishers U 48003202 roysched U 80003316 sales U 112003430 salesdetail U 144003544 titleauthor U 176003658 titles U 208003772 stores U 240003886 discounts U 272004000 au_pix U 304004114 blurbs U 336004228 friends_etc U 704005539 test U 912006280 hello U 1056006793 Using control-of-flow language 456 Adaptive Server Enterprise (14 rows affected) if...else constructs are frequently used in stored procedures where they test for the existence of some parameter. if tests can nest within other if tests, either within another if or following an else. The expression in the if test can return only one value. Also, for each if...else construct, there can be one select statement for the if and one for the else. To include more than one select statement, use the begin...end keywords. The maximum number of if tests you can nest varies, depending on the complexity of the select statements (or other language constructs) you include with each if...else construct. case expression case expression simplifies many conditional Transact-SQL constructs. Instead of using a series of if statements, case expression allows you to use a series of conditions that return the appropriate values when the conditions are met. case expression is ANSI SQL92 compliant. With case expression, you can: • Simplify queries and write more efficient code • Convert data between the formats used in the database (such as int) and the format used in an application (such as char) • Return the first non-null value in a list of columns • Compare two values and return the first value if the values do not match, or a NULL value if the values do match • Write queries that avoid division by 0 case expression includes the keywords case, when, then, coalesce, and nullif. coalesce and nullif are an abbreviated form of case expression. For details on case expression syntax, see the Reference Manual. CHAPTER 14 Using Batches and Control-of-Flow Language Transact-SQL User’s Guide 457 Using case expression for alternative representation Using case expression you can represent data in a manner that is more meaningful to the user. For example, the pubs2 database stores a 1 or a 0 in the contract column of the titles table to indicate the status of the book’s contract. However, in your application code or for user interaction, you may prefer to use the words “Contract” or “No Contract” to indicate the status of the book. To select the type from the titles table using the alternative representation: select title, "Contract Status" = case when contract = 1 then "Contract" when contract = 0 then "No Contract" end from titles title Contract Status ----- --------------- The Busy Executive’s Database Guide Contract Cooking with Computers: Surreptitio Contract You Can Combat Computer Stress! Contract . . . The Psychology of Computer Cooking No Contract . . . Fifty Years in Buckingham Palace Contract Sushi, Anyone? Contract (18 rows affected) case and division by zero case expression allows you to write queries that avoid division by zero (called exception avoidance). For example, if you attempt to divide the total_sales column for each book by the advance column, the query results in division by zero when the query attempts to divide the total_sales (2032) of title_id MC2222 by the advance (0.00): select title_id, total_sales, advance, total_sales/advance from titles title_id total_sales advance ------- ----------- --------- ------ BU1032 4095 5,000.00 0.82 BU1111 3876 5,000.00 0.78 BU2075 18722 10,125.00 1.85 BU7832 4095 5,000.00 0.82 Divide by zero occurred.Using control-of-flow language 458 Adaptive Server Enterprise You can use a case expression to avoid this by not allowing the zero to figure in the equation. In this example, when the query comes across the zero, it returns a predefined value, rather than performing the division: select title_id, total_sales, advance, "Cost Per Book" = case when advance != 0 then convert(char, total_sales/advance) else "No Books Sold" end from titles title_id total_sales advance Cost Per Book -------- ----------- ---------- ------------- BU1032 4095 5,000.00 0.82 BU1111 3876 5,000.00 0.78 BU2075 18722 10,125.00 1.85 BU7832 4095 5,000.00 0.82 MC2222 2032 0.00 No Books Sold MC3021 22246 15,000.00 1.48 MC3026 NULL NULL No Books Sold . . . TC3218 375 7,000.00 0.05 TC4203 15096 4,000.00 3.77 TC7777 4095 8,000.00 0.51 (18 rows affected) The division by zero for title_id MC2222 no longer prevents the query from running. Also, the null values for MC3021 do not prevent the query from running. Using rand() functions in case expressions Expressions that reference the rand function, the getdate function, and so on, produce different values each time they are evaluated. This can yield unexpected results when you use these expressions in certain case expressions. For example, the SQL standard specifies that case expressions with the form: case expression when value1 then result1 when value2 then result2 when value3 then result3 ... end are equivalent to the following form of case expression:CHAPTER 14 Using Batches and Control-of-Flow Language Transact-SQL User’s Guide 459 case expression when expression=value1 then result1 when expression=value2 then result2 when expression=value3 then result3 ... end This definition explicitly requires that the expression be evaluated repeatedly in each when clause that is examined. This definition of case expressions affects case expressions that reference functions such as the rand function. For example, the following case expression: select CASE convert(int, (RAND() * 3)) when 0 then "A" when 1 then "B" when 2 then "C" when 3 then "D" else "E" end is defined to be equivalent to the following according to the SQL standard: select CASE when convert(int, (RAND() * 3)) = 0 then "A" when convert(int, (RAND() * 3)) = 1 then "B" when convert(int, (RAND() * 3)) = 2 then "C" when convert(int, (RAND() * 3)) = 3 then "D" else "E" end In this form, a new rand value is generated for each when clause, and the case expression frequently produce the result “E”. case expression results The rules for determining the datatype of a case expression are based on the same rules that determine the datatype of a column in a union operation. A case expression has a series of alternative result expressions (R1, R2, ..., Rn in the example below) which are specified by the then and else clauses. For example: case when search_condition1 then R1 when search_condition2 then R2 ... else Rn endUsing control-of-flow language 460 Adaptive Server Enterprise The datatypes of the result expressions R1, R2, ..., Rn are used to determine the overall datatype of case. The same rules that determine the datatype of a column of a union that specifies n tables, and has the expressions R1, R2, …, Rn as the ith column, also determine the datatype of a case expression. The datatype of case is determined in the same manner as would be determined by the following query: select...R1...from ... union select...R2...from... union... ... select...Rn...from... Not all datatypes are compatible, and if you specify two datatypes that are incompatible (for example, char and int), your Transact-SQL query will fail. For more information about the union-datatype rules, see the Reference Manual. case expression requires at least one non-null result At least one result from the case expression must return a value other than null. The following query: select price, case when title_id like "%" then NULL when pub_id like "%" then NULL end from titles returns the error message: All result expressions in a CASE expression must not be NULL case Using case expression, you can test for conditions that determine the result set. The syntax is: case when search_condition1 then result1 when search_condition2 then result2 . . . when search_conditionn then resultnCHAPTER 14 Using Batches and Control-of-Flow Language Transact-SQL User’s Guide 461 else resultx end where search_condition is a logical expression, and result is an expression. If search_condition1 is true, the value of case is result1; if search_condition1 is not true, search_condition2 is checked. If search_condition2 is true, the value of case is result2, and so on. If none of the search conditions are true, the value of case is resultx. The else clause is optional. If it is not used, the default is else NULL. end indicates the end of the case expression. The total sales of each book for each store are kept in the salesdetail table. If you want to show a series of ranges for the book sales, you could track how each book sold at each store, using the following ranges: • Books that sold less than 1000 (low-selling books) • Books that sold between 1000 and 3000 (medium-selling books) • Books that sold more than 3000 (high-selling books) You would write the following query: select stor_id, title_id, qty, "Book Sales Catagory" = case when qty < 1000 then "Low Sales Book" when qty >= 1000 and qty <= 3000 then "Medium Sales Book" when qty > 3000 then "High Sales Book" end from salesdetail group by title_id stor_id title_id qty Book Sales Catagory ------- -------- ---- ------------------ 5023 BU1032 200 Low Sales Book 5023 BU1032 1000 Low Sales Book 7131 BU1032 200 Low Sales Book . . . 7896 TC7777 75 Low Sales Book 7131 TC7777 80 Low Sales Book 5023 TC7777 1000 Low Sales Book 7066 TC7777 350 Low Sales Book 5023 TC7777 1500 Medium Sales Book 5023 TC7777 1090 Medium Sales Book (116 rows affected)Using control-of-flow language 462 Adaptive Server Enterprise The following example selects the titles from the titleauthor table according to the author’s royalty percentage (royaltyer) and then assigns each title with a value of High, Medium, or Low royalty: select title, royaltyper, "Royalty Category" = case when (select avg(royaltyper) from titleauthor tta where t.title_id = tta.title_id) > 60 then "High Royalty" when (select avg(royaltyper) from titleauthor tta where t.title_id = tta.title_id) between 41 and 59 then "Medium Royalty" else "Low Royalty" end from titles t, titleauthor ta where ta.title_id = t.title_id order by title title royaltyper royalty Category ------- ---------- ---------------- But Is It User Friendly? 100 High Royalty Computer Phobic and Non-Phobic Ind 25 Medium Royalty Computer Phobic and Non-Phobic Ind 75 Medium Royalty Cooking with Computers: Surreptiti 40 Medium Royalty Cooking with Computers: Surreptiti 60 Medium Royalty Emotional Security: A New Algorith 100 High Royalty . . . Sushi, Anyone? 40 Low Royalty The Busy Executive’s Database Guide 40 Medium Royalty The Busy Executive’s Database Guide 60 Medium Royalty The Gourmet Microwave 75 Medium Royalty You Can Combat Computer Stress! 100 High Royalty (25 rows affected) case and value comparisons This form of case is used for value comparisons. It allows only an equality check between two values; no other comparisons are allowed. The syntax is: case valueT when value1 then result1 when value2 then result2 . . . when valuen then resultn else resultx endCHAPTER 14 Using Batches and Control-of-Flow Language Transact-SQL User’s Guide 463 where value and result are expressions. If valueT equals value1, the value of the case is result1. If valueT does not equal value1, valueT is compared to value2. If valueT equals value2, then the value of the case is result2, and so on. If valueT does not equal the value of value1 through valuen, the value of the case is resultx. At least one result must be non-null. All the result expressions must be compatible. Also, all values must be compatible. The syntax described above is equivalent to: case when valueT = value1 then result1 when valueT = value2 then result2 . . . when valueT = valuen then resultn else resultx end This is the same format used for case and search conditions (see “case” on page 460 for more information about this syntax). The following example selects the title and pub_id from the titles table and specifies the publisher for each book based on the pub_id: select title, pub_id, "Publisher" = case pub_id when "0736" then "New Age Books" when "0877" then "Binnet & Hardley" when "1389" then "Algodata Infosystems" else "Other Publisher" end from titles order by pub_id title pub_id Publisher ----- ------ ------------- Life Without Fear 0736 New Age Books Is Anger the Enemy? 0736 New Age Books You Can Combat Computer 0736 New Age Books . . . Straight Talk About Computers 1389 Algodata Infosystems The Busy Executive’s Database 1389 Algodata Infosystems Cooking with Computers: Surre 1389 Algodata Infosystems (18 rows affected) This is equivalent to the following query, which uses a case and search condition syntax:Using control-of-flow language 464 Adaptive Server Enterprise select title, pub_id, "Publisher" = case when pub_id = "0736" then "New Age Books" when pub_id = "0877" then "Binnet & Hardley" when pub_id = "1389" then "Algodata Infosystems" else "Other Publisher" end from titles order by pub_id coalesce coalesce examines a series of values (value1, value2, ..., valuen) and returns the first non-null value. The syntax of coalesce is: coalesce(value1, value2, ..., valuen) Where value1, value2, ..., valuen are expressions. If value1 is non-null, the value of coalesce is value1; if value1 is null, value2 is examined, and so on. The examination continues until a non-null value is found. The first non-null value becomes the value of coalesce. When you use coalesce, Adaptive Server translates it internally to the following format: case when value1 is not NULL then value1 when value2 is not NULL then value2 . . . when valuen-1 is not NULL then valuen-1 else valuen end valuen-1 refers to the next to last value, before the final value, valuen. The example below uses coalesce to determine whether a store orders a low quantity (more than 100 but less than 1000) or a high quantity of books (more than 1000): select stor_id, discount, "Quantity" = coalesce(lowqty, highqty) from discounts stor_id discount Quantity ------- -------- --------- ---- NULL 10.500000 NULL NULL 6.700000 100 NULL 10.000000 1001 8042 5.000000 NULL CHAPTER 14 Using Batches and Control-of-Flow Language Transact-SQL User’s Guide 465 (4 rows affected) nullif nullif compares two values; if the values are equal, nullif returns a null value. If the two values are not equal, nullif returns the value of the first value. This is useful for finding any missing, unknown, or inapplicable information that is stored in an encoded form. For example, values that are unknown are sometimes historically stored as -1. Using nullif, you can replace the -1 values with null and get the null behavior defined by Transact-SQL. The syntax is: nullif(value1, value2) If value1 equals value2, nullif returns NULL. If value1 does not equal value2, nullif returns value1. value1 and value2 are expressions, and their datatypes must be comparable When you use nullif, Adaptive Server translates it internally to the following format: case when value1 = value2 then NULL else value1 end For example, the titles table uses the value “UNDECIDED” to represent books whose type category is not yet determined. The following query performs a search on the titles table for book types; any book whose type is “UNDECIDED” is returned as type NULL (the following output is reformatted for display purposes): select title, "type"= nullif(type, "UNDECIDED") from titles title type ----- -------- The Busy Executive’s Database Guide business Cooking with Computers: Surreptiti business You Can Combat Computer Stress! business . . . The Psychology of Computer Cooking NULL Fifty Years in Buckingham Palace K trad_cook Sushi, Anyone? trad_cook (18 rows affected)Using control-of-flow language 466 Adaptive Server Enterprise Notice that The Psychology of Computing is stored in the table as “UNDECIDED”, but the query returns it as type NULL. begin...end The begin and end keywords enclose a series of statements so that they are treated as a unit by control-of-flow constructs like if...else. A series of statements enclosed by begin and end is called a statement block. The syntax of begin...end is: begin statement block end Here is an example: if (select avg(price) from titles) < $15 begin update titles set price = price * 2 select title, price from titles where price > $28 end Without begin and end, the if condition applies only to the first Transact-SQL statement. The second statement executes independently of the first. begin...end blocks can nest within other begin...end blocks. while and break...continue while sets a condition for the repeated execution of a statement or statement block. The statements are executed repeatedly as long as the specified condition is true. The syntax is: while boolean_expression statement In this example, the select and update statements are repeated, as long as the average price remains less than $30: while (select avg(price) from titles) < $30 CHAPTER 14 Using Batches and Control-of-Flow Language Transact-SQL User’s Guide 467 begin select title_id, price from titles where price > $20 update titles set price = price * 2 end (0 rows affected) title_id price ------ ------- PC1035 22.95 PS1372 21.59 TC3218 20.95 (3 rows affected) (18 rows affected) (0 rows affected) title_id price ------ ------- BU1032 39.98 BU1111 23.90 BU7832 39.98 MC2222 39.98 PC1035 45.90 PC8888 40.00 PS1372 43.18 PS2091 21.90 PS3333 39.98 TC3218 41.90 TC4203 23.90 TC7777 29.98 (12 rows affected) (18 rows affected) (0 rows affected) break and continue control the operation of the statements inside a while loop. break causes an exit from the while loop. Any statements that appear after the end keyword that marks the end of the loop are executed. continue causes the while loop to restart, skipping any statements after continue but inside the loop. break and continue are often activated by an if test. The syntax for break...continue is: while boolean expression begin Using control-of-flow language 468 Adaptive Server Enterprise statement [statement]... break [statement]... continue [statement]... end Here is an example using while, break, continue, and if that reverses the inflation caused in the previous examples. As long as the average price remains more than $20, all the prices are cut in half. The maximum price is then selected. If it is less than $40, the while loop is exited; otherwise, it will try to loop again. continue allows print to execute only when the average is more than $20. After the while loop ends, a message and a list of the highest priced books print. while (select avg(price) from titles) > $20 begin update titles set price = price / 2 if (select max(price) from titles) < $40 break else if (select avg(price) from titles) < $20 continue print "Average price still over $20" end select title_id, price from titles where price > $20 print "Not Too Expensive" (18 rows affected) (0 rows affected) (0 rows affected) Average price still over $20 (0 rows affected) (18 rows affected) (0 rows affected) title_id price -------- ------- PC1035 22.95 PS1372 21.59 TC3218 20.95 (3 rows affected) Not Too ExpensiveCHAPTER 14 Using Batches and Control-of-Flow Language Transact-SQL User’s Guide 469 If two or more while loops are nested, break exits to the next outermost loop. First, all the statements after the end of the inner loop execute. Then, the outer loop restarts. declare and local variables Local variables are declared, named, and typed with the declare keyword and are assigned an initial value with a select statement. They must be declared, assigned a value, and used within the same batch or procedure. See “Local variables” on page 478 for more information. goto The goto keyword causes unconditional branching to a user-defined label. goto and labels can be used in stored procedures and batches. A label’s name must follow the rules for identifiers and must be followed by a colon when it is first given. It is not followed by a colon when it is used with goto. Here is the syntax: label: goto label Here is an example that uses goto and a label, a while loop, and a local variable as a counter: declare @count smallint select @count = 1 restart: print "yes" select @count = @count + 1 while @count <=4 goto restart goto is usually made dependent on a while or if test or some other condition, to avoid an endless loop between goto and the label. Using control-of-flow language 470 Adaptive Server Enterprise return The return keyword exits from a batch or procedure unconditionally. It can be used at any point in a batch or a procedure. When used in stored procedures, return can accept an optional argument to return a status to the caller. Statements after return are not executed. The syntax is: return [int_expression] Here is an example of a stored procedure that uses return as well as if...else and begin...end: create procedure findrules @nm varchar(30) = null as if @nm is null begin print "You must give a user name" return end else begin select sysobjects.name, sysobjects.id, sysobjects.uid from sysobjects, master..syslogins where master..syslogins.name = @nm and sysobjects.uid = master..syslogins.suid and sysobjects.type = "R" end If no user name is given as a parameter when findrules is called, the return keyword causes the procedure to exit after a message has been sent to the user’s screen. If a user name is given, the names of the rules owned by the user are retrieved from the appropriate system tables. return is similar to the break keyword used inside while loops. Examples using return values are included in Chapter 15, “Using Stored Procedures.” print The print keyword, used in the previous example, displays a user-defined message or the contents of a local variable on the user’s screen. The local variable must be declared within the same batch or procedure in which it is used. The message itself can be up to 255 bytes long. CHAPTER 14 Using Batches and Control-of-Flow Language Transact-SQL User’s Guide 471 The syntax is: print {format_string | @local_variable | @@global_variable} [,arg_list] For example: if exists (select postalcode from authors where postalcode = "94705") print "Berkeley author" Here is how to use print to display the contents of a local variable: declare @msg char(50) select @msg = "What’s up, doc?" print @msg print recognizes placeholders in the character string to be printed out. Format strings can contain up to 20 unique placeholders in any order. These placeholders are replaced with the formatted contents of any arguments that follow format_string when the text of the message is sent to the client. To allow reordering of the arguments when format strings are translated to a language with a different grammatical structure, the placeholders are numbered. A placeholder for an argument appears in this format: %nn!. The components are a percent sign, followed by an integer from 1 to 20, followed by an exclamation point. The integer represents the placeholder position in the string in the original language. “%1!” is the first argument in the original version, “%2!” is the second argument, and so on. Indicating the position of the argument in this way makes it possible to translate correctly even when the order in which the arguments appear in the target language is different from their order in the source language. For example, assume the following is an English message: %1! is not allowed in %2!. The German version of this message is: %1! ist in %2! nicht zulässig. The Japanese version of the message is: Using control-of-flow language 472 Adaptive Server Enterprise Figure 14-1: Japanese message In this example, “%1!” in all three languages represents the same argument, and “%2!” also represents a single argument in all three languages. This example shows the reordering of the arguments that is sometimes necessary in the translated form. You cannot skip placeholder numbers when using placeholders in a format string, although placeholders do not have to be used in numerical order. For example, you cannot have placeholders 1 and 3 in a format string without having placeholder 2 in the same string. The optional arg_list can be a series of either variables or constants. An argument can be any datatype except text or image; it is converted to the char datatype before it is included in the final message. If no argument list is provided, the format string must be the message to be printed, without any placeholders. The maximum output string length of format_string plus all arguments after substitution is 512 bytes. raiserror raiserror both displays a user-defined error or local variable message on the user’s screen and sets a system flag to record the fact that an error has occurred. As with print, the local variable must be declared within the same batch or procedure in which it is used. The message can be up to 255 characters long. Here is the syntax for raiserror: raiserror error_number [{format_string | @local_variable}] [, arg_list] [extended_value = extended_value [{, extended_value = extended_value}...]] The error_number is placed in the global variable error@@, which stores the error number most recently generated by Adaptive Server. Error numbers for user-defined error messages must be greater than 17,000. If the error_number is between 17,000 and 19,999, and format_string is missing or empty (““), Adaptive Server retrieves error message text from the sysmessages table in the master database. These error messages are used chiefly by system procedures.CHAPTER 14 Using Batches and Control-of-Flow Language Transact-SQL User’s Guide 473 The length of the format_string alone is limited to 255 bytes; the maximum output length of format_string plus all arguments is 512 bytes. Local variables used for raiserror messages must be char or varchar. The format_string or variable is optional; if you do not include one, Adaptive Server uses the message corresponding to the error_number from sysusermessages in the default language. As with print, you can substitute variables or constants defined by arg_list in the format_string. As an option, you can define extended error data for use by an Open Client™ application (when you include extended_values with raiserror). For more information about extended error data, see your Open Client documentation or raiserror in the Reference Manual. Use raiserror instead of print when you want an error number stored in error@@. For example, here is how you could use raiserror in the procedure findrules: raiserror 99999 "You must give a user name" The severity level of all user-defined error messages is 16, which indicates that the user has made a nonfatal mistake. Creating messages for print and raiserror You can call messages from sysusermessages for use by either print or raiserror with sp_getmessage. Use sp_addmessage to create a set of messages. The example that follows uses sp_addmessage, sp_getmessage, and print to install a message in sysusermessages in both English and German, retrieve it for use in a user-defined stored procedure, and print it. /* ** Install messages ** First, the English (langid = NULL) */ set language us_english go sp_addmessage 25001, "There is already a remote user named ’%1!’ for remote server ’%2!’." go /* Then German*/ sp_addmessage 25001, "Remotebenutzername ’%1!’ existiert bereits auf dem Remoteserver ’%2!’.","german"Using control-of-flow language 474 Adaptive Server Enterprise go create procedure test_proc @remotename varchar(30), @remoteserver varchar(30) as declare @msg varchar(255) declare @arg1 varchar(40) /* ** check to make sure that there is not ** a @remotename for the @remoteserver. */ if exists (select * from master.dbo.sysremotelogins l, master.dbo.sysservers s where l.remoteserverid = s.srvid and s.srvname = @remoteserver and l.remoteusername = @remotename) begin exec sp_getmessage 25001, @msg output select @arg1=isnull(@remotename, "null") print @msg, @arg1, @remoteserver return (1) end return(0) go You can also bind user-defined messages to constraints, as described in “Creating error messages for constraints” on page 265. To drop a user-defined message, use sp_dropmessage. To change a message, drop it with sp_dropmessage and add it again with sp_addmessage. waitfor The waitfor keyword specifies a specific time of day, a time interval, or an event at which the execution of a statement block, stored procedure, or transaction is to occur. The syntax is: waitfor {delay "time" | time "time" | errorexit | processexit | mirrorexit} where delay time instructs Adaptive Server to wait until the specified period of time has passed. time time instructs Adaptive Server to wait until the specified time, given in one of the valid formats for datetime data. CHAPTER 14 Using Batches and Control-of-Flow Language Transact-SQL User’s Guide 475 However, you cannot specify dates—the date portion of the datetime value is not allowed. The time you specify with waitfor time or waitfor delay can include hours, minutes, and seconds—up to a maximum of 24 hours. Use the format “hh:mm:ss”. For example, the following command instructs Adaptive Server to wait until 4:23 p.m.: waitfor time "16:23" This command instructs Adaptive Server to wait 1 hour and 30 minutes: waitfor delay "01:30" For a review of the formats for time values, see “Entering times” on page 318. errorexit instructs Adaptive Server to wait until a process terminates abnormally. processexit waits until a process terminates for any reason. mirrorexit waits until a read or write to a mirrored device fails. You can use waitfor errorexit with a procedure that kills the abnormally terminated process to free system resources that would otherwise be taken up by an infected process. To find out which process is infected, use sp_who to check the sysprocesses table. The following example instructs Adaptive Server to wait until 2:20 p.m. Then, it updates the chess table with the next move and executes a stored procedure called sendmessage, which inserts a message into one of Judy’s tables notifying her that a new move now exists in the chess table. begin waitfor time "14:20" insert chess(next_move) values("Q-KR5") execute sendmessage "Judy" end To send the message to Judy after 10 seconds instead of waiting until 2:20, substitute this waitfor statement in the preceding example: waitfor delay "0:00:10" After you give the waitfor command, you cannot use your connection to Adaptive Server until the time or event that you specified occurs.Using control-of-flow language 476 Adaptive Server Enterprise Comments Use the comment notation to attach comments to statements, batches, and stored procedures. Comments are not executed. You can insert a comment on a line by itself or at the end of a command line. Two comment styles are available: the “slash-asterisk” style: /* text of comment */ and the “double-hyphen” style: -- text of comment You cannot use the double hyphen style for multi-line comments. There is no maximum length for comments. Slash-asterisk style comments The /* style comment is a Transact-SQL extension. Multiple-line comments are acceptable, as long as each comment starts with “/*” and ends with “*/”. Everything between “/*” and “*/” is treated as part of the comment. The /* form permits nesting. A stylistic convention often used for multiple-line comments is to begin the first line with “/*” and subsequent lines with “**”. The comment is ended with “*/” as usual: select * from titles /* A comment here might explain the rules ** associated with using an asterisk as ** shorthand in the select list.*/ where price > $5 This procedure includes a couple of comments: /* this procedure finds rules by user name*/ create procedure findmyrule @nm varchar(30) = null as if @nm is null begin print "You must give a user name" return print "I have returned" /* this statement follows return, ** so won’t be executed */ end else /* print the rule names and IDs, and the user ID */ CHAPTER 14 Using Batches and Control-of-Flow Language Transact-SQL User’s Guide 477 select sysobjects.name, sysobjects.id, sysobjects.uid from sysobjects, master..syslogins where master..syslogins.name = @nm and sysobjects.uid = master..syslogins.suid and sysobjects.type = "R" Double-hyphen style comments This comment style begins with two consecutive hyphens followed by a space (-- ) and terminates with a newline character. Therefore, multiple-line comments are not possible. Adaptive Server does not interpret two consecutive hyphens within a string literal or within a /*-style comment as signaling the beginning of a comment. To represent an expression that contains two consecutive minus signs (binary followed by unary), put a space or an opening parenthesis between the two hyphens. Following are examples: -- this procedure finds rules by user name create procedure findmyrule @nm varchar(30) = null as if @nm is null begin print "You must give a user name" return print "I have returned" -- each line of a multiple-line comment -- must be marked separately. end else -- print the rule names and IDs, and -- the user ID select sysobjects.name, sysobjects.id, sysobjects.uid from sysobjects, master..syslogins where master..syslogins.name = @nm and sysobjects.uid = master..syslogins.suid and sysobjects.type = "R" Local variables 478 Adaptive Server Enterprise Local variables Local variables are often used as counters for while loops or if...else blocks in a batch or stored procedure. When they are used in stored procedures, they are declared for automatic, non-interactive use by the procedure when it executes. You can use variables nearly anywhere the Transact-SQL syntax indicates that an expression can be used, such as char_expr, integer_expression, numeric_expr, or float_expr. Declaring local variables To declare a local variable’s name and datatype use: declare @variable_name datatype [, @variable_name datatype]... The variable name must be preceded by the @ sign and conform to the rules for identifiers. Specify either a user-defined datatype or a system-supplied datatype other than text, image, or sysname. It is more efficient in terms of memory and performance to write: declare @a int, @b char(20), @c float than to write: declare @a int declare @b char(20) declare @c float Local variables and select statements When you declare a variable, it has the value NULL. Assign values to local variables with a select statement. Here is the syntax: select @variable_name = {expression | (select_statement)} [, @variable = {expression | (select_statement)}...] [from clause] [where clause] [group by clause] [having clause] [order by clause] [compute clause] As with declare statements, it is more efficient to write: select @a = 1, @b = 2, @c = 3 than to write: CHAPTER 14 Using Batches and Control-of-Flow Language Transact-SQL User’s Guide 479 select @a = 1 select @b = 2 select @c = 3 Do not use a single select statement to assign a value to one variable and then to another whose value is based on the first. Doing so can yield unpredictable results. For example, the following queries both try to find the value of @c2. The first query yields NULL, while the second query yields the correct answer, 0.033333: /* this is wrong*/ declare @c1 float, @c2 float select @c1 = 1000/1000, @c2 = @c1/30 select @c1, @c2 /* do it this way */ declare @c1 float, @c2 float select @c1 = 1000/1000 select @c2 = @c1/30 select @c1 , @c2 You cannot use a select statement that assigns values to variables to also return data to the user. The first select statement in the following example assigns the maximum price to the local variable @veryhigh; the second select statement is needed to display the value: declare @veryhigh money select @veryhigh = max(price) from titles select @veryhigh If the select statement that assigns values to a variable returns more than one value, the last value that is returned is assigned to the variable. The following query assigns the variable the last value returned by “select advance from titles”. declare @m money select @m = advance from titles select @m (18 rows affected) ------------------------ 8,000.00 (1 row affected) The assignment statement indicates how many rows were affected (returned) by the select statement.Local variables 480 Adaptive Server Enterprise If a select statement that assigns values to a variable fails to return any values, the variable is left unchanged by the statement. Local variables can be used as arguments to print or raiserror. If you are using variables in an update statement, see “Using the set clause with update” on page 339. Local variables and update statements You can assign variables directly in an update statement. You do not need to use a select statement to assign a value to a variable. When you declare a variable, it has the value NULL. Here is the syntax: update [[database.]owner.] {table_name | view_name} set [[[database.]owner.]{table_name. | view_name.}] column_name1 = {expression1 | null | (select_statement)} | variable_name1 = {expression1 | null} [, column_name2 = {expression2 | null | (select_statement)}]... | [, variable_name2 = {expression2 | null}]... [from [[database.]owner.]{table_name | view_name} [, [[database.]owner.] {table_name | view_name}]]... [where search_conditions] Local variables and subqueries A subquery that assigns a value to the local variable must return only one value. Here are some examples: declare @veryhigh money select @veryhigh = max(price) from titles if @veryhigh > $20 print "Ouch!" declare @one varchar(18), @two varchar(18) select @one = "this is one", @two = "this is two" if @one = "this is one" print "you got one" if @two = "this is two" print "you got two" else print "nope" declare @tcount int, @pcount int CHAPTER 14 Using Batches and Control-of-Flow Language Transact-SQL User’s Guide 481 select @tcount = (select count(*) from titles), @pcount = (select count(*) from publishers) select @tcount, @pcount Local variables and while loops and if…else blocks The following example uses local variables in a counter in a while loop, for doing matching in a where clause, in an if statement, and for setting and resetting values in select statements: /* Determine if a given au_id has a row in au_pix*/ /* Turn off result counting */ set nocount on /* declare the variables */ declare @c int, @min_id varchar(30) /*First, count the rows*/ select @c = count(*) from authors /* Initialize @min_id to "" */ select @min_id = "" /* while loop executes once for each authors row */ while @c > 0 begin /*Find the smallest au_id*/ select @min_id = min(au_id) from authors where au_id > @min_id /*Is there a match in au_pix?*/ if exists (select au_id from au_pix where au_id = @min_id) begin print "A Match! %1!", @min_id end select @c = @c -1 /*decrement the counter */ end Variables and null values Local variables are assigned the value NULL when they are declared, and may be assigned the null value by a select statement. The special meaning of NULL requires that the comparison between null-value variables and other null values follow special rules.Local variables 482 Adaptive Server Enterprise Table 14-2 shows the results of comparisons between null-value columns and null-value expressions using different comparison operators. An expression can be a variable, a literal, or a combination of variables and literals and arithmetic operators. Table 14-2: Comparing null values For example, this test: declare @v int, @i int if @v = @i select "null = null, true" if @v > @i select "null > null, true" shows that only the first comparison returns true: ----------------- null = null, true (1 row affected) This example returns all the rows from the titles table where the advance has the value NULL: declare @m money select title_id, advance from titles where advance = @m title_id advance -------- ---------------- MC3026 NULL PC9999 NULL (2 rows affected) Type of comparison Using the = operator Using the <, >, <=, !=, !<, !>, or <> operator Comparing column_value to column_value FALSE FALSE Comparing column_value to expression TRUE FALSE Comparing expression to column_value TRUE FALSE Comparing expression to expression TRUE FALSECHAPTER 14 Using Batches and Control-of-Flow Language Transact-SQL User’s Guide 483 Global variables Global variables are system-supplied, predefined variables. They are distinguished from local variables by the two @ signs preceding their names— for example, @@error. The two @ signs are considered part of the identifier used to define the global variable. Users cannot create global variables and cannot update the value of global variables directly in a select statement. If a user declares a local variable that has the same name as a global variable, that variable is treated as a local variable. Transactions and global variables Some global variables provide information to use in transactions. Checking for errors with @@error The @@error global variable is commonly used to check the error status of the most recently executed batch in the current user session. @@error contains 0 if the last transaction succeeded; otherwise @@error contains the last error number generated by the system. A statement such as if @@error != 0 followed by return causes an exit on error. Every Transact-SQL statement, including print statements and if tests, resets @@error, so the status check must immediately follow the batch whose success is in question. The @@sqlstatus global variable has no effect on @@error output. See “Checking the status from the last fetch” on page 484 for details. Checking IDENTITY values with @@identity @@identity contains the last value inserted into an IDENTITY column in the current user session. @@identity is set each time an insert, select into, or bcp attempts to insert a row into a table. The value of @@identity is not affected by the failure of an insert, select into, or bcp statement or the rollback of the transaction that contained it. @@identity retains the last value inserted into an IDENTITY column, even if the statement that inserted it fails to commit. If a statement inserts multiple rows, @@identity reflects the IDENTITY value for the last row inserted. If the affected table does not contain an IDENTITY column, @@identity is set to 0.Global variables 484 Adaptive Server Enterprise Checking the transaction nesting level with @@trancount @@trancount contains the nesting level of transactions in the current user session. Each begin transaction in a batch increments the transaction count. When you query @@trancount in chained transaction mode, its value is never 0 because the query automatically initiates a transaction. Checking the transaction state with @@transtate @@transtate contains the current state of a transaction after a statement executes in the current user session. However, unlike @@error, @@transtate does not get cleared for each batch. @@transtate may contain the values in Table 14-3: Table 14-3: @@transtate values @@transtate only changes due to execution errors. Syntax and compile errors do not affect the value of @@transtate. See “Checking the state of transactions” on page 637 for examples showing @@transtate in transactions. Checking the nesting level with @@nestlevel @@nestlevel contains the nesting level of current execution with the user session, initially 0. Each time a stored procedure or trigger calls another stored procedure or trigger, the nesting level is incremented. If the maximum of 16 is exceeded, the transaction aborts. Checking the status from the last fetch @@sqlstatus contains status information resulting from the last fetch statement for the current user session. @@sqlstatus may contain the following values: Value Meaning 0 Transaction in progress: an explicit or implicit transaction is in effect; the previous statement executed successfully. 1 Transaction succeeded: the transaction completed and committed its changes. 2 Statement aborted: the previous statement was aborted; no effect on the transaction. 3 Transaction aborted: the transaction aborted and rolled back any changes.CHAPTER 14 Using Batches and Control-of-Flow Language Transact-SQL User’s Guide 485 Table 14-4: @@sqlstatus values @@sqlstatus has no effect on @@error output. For example, the following batch sets @@sqlstatus to 1 by causing the fetch@@error statement to result in an error. However, @@error reflects the number of the error message, not the @@sqlstatus output: declare csr1 cursor for select * from sysmessages for read only open csr1 begin declare @xyz varchar(255) fetch csr1 into @xyz select error = @@error select sqlstatus = @@sqlstatus end Msg 553, Level 16, State 1: Line 3: The number of parameters/variables in the FETCH INTO clause does not match the number of columns in cursor ’csr1’ result set. At this point, the @@error global variable is set to 553, the number of the last generated error. @@sqlstatus is set to 1. Global variables affected by set options set options can customize the display of results, show processing statistics, and provide other diagnostic aids for debugging your Transact-SQL programs. Table 14-5 lists the global variables that contain information about the session options controlled by the set command. Value Meaning 0 The fetch statement completed successfully. 1 The fetch statement resulted in an error. 2 There is no more data in the result set. This warning occurs if the current cursor position is on the last row in the result set and the client submits a fetch command for that cursor.Global variables 486 Adaptive Server Enterprise Table 14-5: Global variables containing session options The @@options global variable contains a hexadecimal representation of the session’s set options.Table 14-6 lists set options and values that work with @@options. Table 14-6: set options and values for @@options For more information on session options, see the set command in the Reference Manual. Global variable Description @@char_convert Contains 0 if character set conversion is not in effect. Contains 1 if character set conversion is in effect. @@isolation Contains the current isolation level of the Transact-SQL program. @@isolation takes the value of the active level (0, 1, or 3). @@options Contains a hexadecimal representation of the session’s set options. @parallel_degree Contains the current maximum parallel degree setting. @@rowcount Contains the number of rows affected by the last query. @@rowcount is set to 0 by any command that does not return rows, such as an if, update, or delete statement. With cursors, @@rowcount represents the cumulative number of rows returned from the cursor result set to the client, up to the last fetch request. @scan_parallel_degree Contains the current maximum parallel degree setting for nonclustered index scans. @@textsize Contains the limit on the number of bytes of text or image data a select returns. Default limit is 32K bytes for isql; the default depends on the client software. Can be changed for a session with set textsize. @@tranchained Contains the current transaction mode of the Transact-SQL program. @@tranchained returns 0 for unchained or 1 for chained. Numeric value Hexidecimal value set option 4 0x04 showplan 5 0x05 noexec 6 0x06 arithignore 8 0x08 arithabort 13 0x0D control 14 0x0E offsets 15 0x0F statistics io and statistics time 16 0x10 parseonly 18 0x12 procid 20 0x14 rowcount 23 0x17 nocountCHAPTER 14 Using Batches and Control-of-Flow Language Transact-SQL User’s Guide 487 Language and character set information in global variables Table 14-7 lists the global variables that contain information about languages and character sets. For more information on languages and character sets, see the System Administration Guide. Table 14-7: Global variables for language and character sets Global variables for monitoring system activity Many global variables report on system activity occurring from the last time Adaptive Server was started. sp_monitor displays the current values of some of the global variables. Table 14-8 lists the global variables that monitor system activity, in the order returned by sp_monitor. For complete information on sp_monitor, see the Reference Manual. Global variable Description @@char_convert Contains 0 if character set conversion is not in effect. Contains 1 if character set conversion is in effect. @@client_csid Contains client’s character set ID. Set to -1 if the client character set has never been initialized; otherwise, it contains the most recently used client character set’s id from syscharsets. @@client_csname Contains client’s character set name. Set to NULL if the client character set has never been initialized; otherwise, it contains the name of the most recently used character set. @@langid Defines the local language ID of the language currently in use, as specified in syslanguages.langid. @@language Defines the name of the language currently in use, as specified in syslanguages.name. @@maxcharlen Contains the maximum length, in bytes, of multibyte characters in the default character set. @@ncharsize Contains the average length, in bytes, of a national character. @@char_convert Contains 0 if character set conversion is not in effect. Contains 1 if character set conversion is in effect.Global variables 488 Adaptive Server Enterprise Table 14-8: Global variables that monitor system activity Server information stored in global variables Table 14-9 lists the global variables that contain miscellaneous information about Adaptive Server. Global variable Description @@connections Contains the number of logins or attempted logins. @@cpu_busy Contains the amount of time, in ticks, that the CPU has spent doing Adaptive Server work since the last time Adaptive Server was started. @@idle Contains the amount of time, in ticks, that Adaptive Server has been idle since it was last started. @@io_busy Contains the amount of time, in ticks, that Adaptive Server has spent doing input and output operations. @@packet_errors Contains the number of errors that occurred while Adaptive Server was sending and receiving packets. @@pack_received Contains the number of input packets read by Adaptive Server since it was last started. @@pack_sent Contains the number of output packets written by Adaptive Server since it was last started. @@total_errors Contains the number of errors that occurred while Adaptive Server was reading or writing. @@total_read Contains the number of disk reads by Adaptive Server since it was last started. @@total_write Contains the number of disk writes by Adaptive Server since it was last started. CHAPTER 14 Using Batches and Control-of-Flow Language Transact-SQL User’s Guide 489 Table 14-9: Global variables containing Adaptive Server information Global variable Description @@cis_version Contains the date and version of Component Integration Services, if it is installed. @@guestuserid The guest user ID. The value is 2. @@invaliduserid The ID for an invalid user. The value is -1 @@max_connections Contains the maximum number of simultaneous connections that can be made with Adaptive Server in the current computer environment. You can configure Adaptive Server for any number of connections less than or equal to the value of @@max_connection, using number of user connections configuration parameter. @@mingroupid Lowest group user ID. The lowest value is 16384. @@minsuid Minimum server user ID. The lowest value is -32768. @@minuserid Lowest user ID. The lowest value is -32768. @@maxgroupid Highest group user ID. The highest value is 1048576 @@maxuserid The highest user ID. The highest value is 2147483647 @@probesuid The probe user ID. The value is 2. @@procid Contains the stored procedure ID of the currently executing procedure. @@servername Contains the name of this Adaptive Server. Define a server name with sp_addserver, and then restart Adaptive Server. @@spid Contains the server process ID number of the current process. @@thresh_hysteresis Contains the decrease in free space required to activate a threshold. This amount, also known as the hysteresis value, is measured in 2K database pages. It determines how closely thresholds can be placed on a database segment. @@timeticks Contains the number of microseconds per tick. The amount of time per tick is machinedependent. @@version Contains the date of the current release of Adaptive Server. @@boottime Displays the time at which Adaptive Server was started.Global variables 490 Adaptive Server Enterprise Global variables and text and image data text and image values can be quite large. When the select list includes text and image values, the limit on the length of the data returned depends on the setting of the @@textsize global variable, which contains the limit on the number of bytes of text or image data a select returns. The default limit is 32K bytes for isql; the default depends on the client software. Change the value for a session with set textsize. Table 14-10 lists the global variables that contain information about text pointers. Note that these global variables are session-based. For more information about text pointers, see “Changing text and image data” on page 342. Table 14-10: Text pointer information stored in global variables Global variable Description @@textcolid Contains the column ID of the column referenced by @@textptr. @@textdbid Contains the database ID of a database containing an object with the column referenced by @@textptr. @@textobjid Contains the object ID of an object containing the column referenced by @@textptr. @@textptr Contains the text pointer of the last text or image column inserted or updated by a process. (Do not confuse this variable with the textptr function.) @@textts Contains the text timestamp of the column referenced by @@textptr. Transact-SQL User’s Guide 491 C H A P T E R 1 5 Using Stored Procedures A stored procedure is a named collection of SQL statements or controlof-flow language. You can create stored procedures for commonly used functions and to increase performance. Adaptive Server also provides system procedures to perform administrative tasks and to update the system tables. This chapter discusses: You can also create and use extended stored procedures to call procedural language functions from Adaptive Server. See Chapter 16, “Using Extended Stored Procedures.” How stored procedures work When you run a stored procedure, Adaptive Server prepares an execution plan so that the procedure’s execution is very fast. Stored procedures can: • Take parameters • Call other procedures • Return a status value to a calling procedure or batch to indicate success or failure and the reason for failure Topic Page How stored procedures work 491 Creating and executing stored procedures 495 Returning information from stored procedures 509 Restrictions associated with stored procedures 517 Renaming stored procedures 519 Using stored procedures as security mechanisms 519 Dropping stored procedures 520 System procedures 520 Getting information about stored procedures 528How stored procedures work 492 Adaptive Server Enterprise • Return values of parameters to a calling procedure or batch • Be executed on remote Adaptive Servers The ability to write stored procedures greatly enhances the power, efficiency, and flexibility of SQL. Compiled procedures dramatically improve the performance of SQL statements and batches. In addition, stored procedures on other Adaptive Servers can be executed if both your server and the remote server are set up to allow remote logins. You can write triggers on your local Adaptive Server that execute procedures on a remote server whenever certain events, such as deletions, updates, or inserts, take place locally. Stored procedures differ from ordinary SQL statements and from batches of SQL statements in that they are precompiled. The first time you run a procedure, Adaptive Server’s query processor analyzes it and prepares an execution plan that is ultimately stored in a system table. Subsequently, the procedure is executed according to the stored plan. Since most of the query processing work has already been performed, stored procedures execute almost instantly. Adaptive Server supplies a variety of stored procedures as convenient tools for the user. The procedures stored in the sybsystemprocs database whose names begin with “sp_” are known as system procedures, because they insert, update, delete and report on data in the system tables. Examples of creating and using stored procedures The syntax for creating a simple stored procedure, without special features such as parameters, is: create procedure procedure_name as SQL_statements Stored procedures are database objects, and their names must follow the rules for identifiers. Any number and kind of SQL statements can be included except for create statements. See “Restrictions associated with stored procedures” on page 517. A procedure can be as simple as a single statement that lists the names of all the users in a database: create procedure namelist as select name from sysusers CHAPTER 15 Using Stored Procedures Transact-SQL User’s Guide 493 To execute a stored procedure, use the keyword execute and the name of the stored procedure, or just use the procedure’s name, as long as it is submitted to Adaptive Server by itself or is the first statement in a batch. You can execute namelist in any of these ways: namelist execute namelist exec namelist To execute a stored procedure on a remote Adaptive Server, you must give the server name. The full syntax for a remote procedure call is: execute server_name.[database_name].[owner].procedure_name The following examples execute the procedure namelist in the pubs2 database on the GATEWAY server: execute gateway.pubs2..namelist gateway.pubs2.dbo.namelist exec gateway...namelist The last example works only if pubs2 is your default database. For information on setting up remote procedure calls on Adaptive Server, see the System Administration Guide. The database name is optional only if the stored procedure is located in your default database. The owner name is optional only if the Database Owner (“dbo”) owns the procedure or if you own it. You must have permission to execute the procedure. A procedure can include more than one statement. create procedure showall as select count(*) from sysusers select count(*) from sysobjects select count(*) from syscolumns When the procedure is executed, the results of each command are displayed in the order that the statement appears in the procedure. showall ------------ 5 (1 row affected) ------------ 88 (1 row affected) How stored procedures work 494 Adaptive Server Enterprise ------------ 349 (1 row affected, return status = 0) When a create procedure command is successfully executed, the procedure’s name is stored in sysobjects, and its source text is stored in syscomments. You can display the source text of a procedure with sp_helptext: sp_helptext showall # Lines of Text --------------- 1 (1 row affected) text ---------------------------------------- create procedure showall as select count(*) from sysusers select count(*) from sysobjects select count(*) from syscolumns (1 row affected, return status = 0) Stored procedures and permissions Stored procedures can serve as security mechanisms, since a user can be granted permission to execute a stored procedure, even if she or he does not have permissions on the tables or views referenced in it or permission to execute specific commands. For details, see the System Administration Guide. You can protect the source text of a stored procedure against unauthorized access by restricting select permission on the text column of the syscomments table to the creator of the procedure and the System Administrator. This restriction is required to run Adaptive Server in the evaluated configuration. To enact this restriction, a System Security Officer must reset the allow select on syscomments.text column parameter using sp_configure. For more information, see the System Administration Guide. Another way to protect access to the source text of a stored procedure is to hide the source text using sp_hidetext. For information, see sp_hidetext in the Reference Manual.CHAPTER 15 Using Stored Procedures Transact-SQL User’s Guide 495 Stored Procedures and Performance As a database changes, you can optimize original query plans used to access its tables by recompiling them with sp_recompile. This saves you from having to find, drop, and re-create every stored procedure and trigger. This example marks every stored procedure and trigger that accesses the table titles to be recompiled the next time it is executed. sp_recompile titles For detailed information about sp_recompile, see the Reference Manual. Creating and executing stored procedures The complete syntax for create procedure is: create procedure [owner.]procedure_name[;number] [[(]@parameter_name datatype [(length) | (precision [, scale ])] [= default] [output] [, @parameter_name datatype [(length) | (precision [, scale])] [= default] [output]]...[)]] [with recompile] as {SQL_statements | external name dll_name} You can create a procedure in the current database only. Permission to issue create procedure defaults to the Database Owner, who can transfer it to other users. Here is the complete syntax statement for execute: [exec[ute]] [@return_status = ] [[[server .]database.]owner.]procedure_name[ ;number] [[@parameter_name =] value | [@parameter_name =] @variable [output] [, [@parameter_name =] value | [@parameter_name =] @variable [output]...]] [with recompile] Creating and executing stored procedures 496 Adaptive Server Enterprise Parameters A parameter is an argument to a stored procedure. You can optionally declare one or more parameters in a create procedure statement. The value of each parameter named in a create procedure statement must be supplied by the user when the procedure is executed. Parameter names must be preceded by an @ sign and must conform to the rules for identifiers, see “Identifiers” on page 7. Parameter names are local to the procedure that creates them; the same parameter names can be used in other procedures. Enclose any parameter value that includes punctuation (such as an object name qualified by a database name or owner name) in single or double quotes. Parameter names, including the @ sign, can be a maximum of 30 bytes long. Parameters must be given a system datatype (except text or image) or a userdefined datatype, and (if required for the datatype) a length or precision and scale in parentheses. Here is a stored procedure for the pubs2 database. Given an author’s last and first names, the procedure displays the names of any books written by that person and the name of each book’s publisher. create proc au_info @lastname varchar(40), @firstname varchar(20) as select au_lname, au_fname, title, pub_name from authors, titles, publishers, titleauthor where au_fname = @firstname and au_lname = @lastname and authors.au_id = titleauthor.au_id and titles.title_id = titleauthor.title_id and titles.pub_id = publishers.pub_id Now, execute au_info: au_info Ringer, Anne au_lname au_fname title pub_name -------- -------- --------------------- ---------- Ringer Anne The Gourmet Microwave Binnet & Hardley Ringer Anne Is Anger the Enemy? New Age Books (2 rows affected, return status = 0) The following stored procedure queries the system tables. Given a table name as the parameter, the procedure displays the table name, index name, and index ID. create proc showind @table varchar(30) as select table_name = sysobjects.name, CHAPTER 15 Using Stored Procedures Transact-SQL User’s Guide 497 index_name = sysindexes.name, index_id = indid from sysindexes, sysobjects where sysobjects.name = @table and sysobjects.id = sysindexes.id The column headings, for example, table_name, were added to improve the readability of the results. Here are acceptable syntax forms for executing this stored procedure: execute showind titles exec showind titles execute showind @table = titles execute GATEWAY.pubs2.dbo.showind titles showind titles The last syntax form, without exec or execute, is acceptable as long as the statement is the only one or the first one in a batch. Here are the results of executing showind in the pubs2 database when titles is given as the parameter: table_name index_name index_id ---------- ---------- ---------- titles titleidind 0 titles titleind 2 (2 rows affected, return status = 0) If you supply the parameters in the form “@parameter = value” you can supply them in any order. Otherwise, you must supply parameters in the order of their create procedure statement. If you supply one value in the form “@parameter = value”, then supply all subsequent parameters this way. This procedure displays the datatype of the qty column from the salesdetail table. create procedure showtype @tabname varchar(18), @colname varchar(18) as select syscolumns.name, syscolumns.length, systypes.name from syscolumns, systypes, sysobjects where sysobjects.id = syscolumns.id and @tabname = sysobjects.name and @colname = syscolumns.name and syscolumns.type = systypes.type When you execute this procedure you can give the @tabname and @colname in a different order from the create procedure statement if you specify them by name:Creating and executing stored procedures 498 Adaptive Server Enterprise exec showtype @colname = qty , @tabname = salesdetail You can use case expressions in any stored procedure where you use a value expression. The following example checks the sales for any book in the titles table: create proc booksales @titleid tid as select title, total_sales, case when total_sales != null then "Books sold" when total_sales = null then "Book sales not available" end from titles where @titleid = title_id For example: booksales MC2222 title total_sales ------------------------ ----------- Silicon Valley Gastronomic Treats 2032 Books sold (1 row affected) Default parameters You can assign a default value for the parameter in the create procedure statement. This value, which can be any constant, is used as the argument to the procedure if the user does not supply one. Here is a procedure that displays the names of all the authors who have written a book published by the publisher given as a parameter. If no publisher name is supplied, the procedure shows the authors published by Algodata Infosystems. create proc pub_info @pubname varchar(40) = "Algodata Infosystems" as select au_lname, au_fname, pub_name from authors a, publishers p, titles t, titleauthor ta where @pubname = p.pub_name and a.au_id = ta.au_id and t.title_id = ta.title_id and t.pub_id = p.pub_id CHAPTER 15 Using Stored Procedures Transact-SQL User’s Guide 499 Note that if the default value is a character string that contains embedded blanks or punctuation, it must be enclosed in single or double quotes. When you execute pub_info, you can give any publisher’s name as the parameter value. If you do not supply any parameter, Adaptive Server uses the default, Algodata Infosystems. exec pub_info au_lname au_fname pub_name -------------- ------------ -------------------- Green Marjorie Algodata Infosystems Bennet Abraham Algodata Infosystems O’Leary Michael Algodata Infosystems MacFeather Stearns Algodata Infosystems Straight Dick Algodata Infosystems Carson Cheryl Algodata Infosystems Dull Ann Algodata Infosystems Hunter Sheryl Algodata Infosystems Locksley Chastity Algodata Infosystems (9 rows affected, return status = 0) This procedure, showind2, assigns “titles” as the default value for the @table parameter: create proc showind2 @table varchar(30) = titles as select table_name = sysobjects.name, index_name = sysindexes.name, index_id = indid from sysindexes, sysobjects where sysobjects.name = @table and sysobjects.id = sysindexes.id The column headings, for example, table_name, clarify the result display. Here is what showind2 shows for the authors table: showind2 authors table_name index_name index_id ----------- ------------- --------- authors auidind 1 authors aunmind 2 (2 rows affected, return status = 0) If the user does not supply a value, Adaptive Server uses the default, titles. showind2 table_name index_name index_id ----------- ----------- ---------Creating and executing stored procedures 500 Adaptive Server Enterprise titles titleidind 1 titles titleind 2 (2 rows affected, return status =0) If a parameter is expected but none is supplied, and a default value is not supplied in the create procedure statement, Adaptive Server displays an error message listing the parameters expected by the procedure. Using default parameters in stored procedures If you create a stored procedure that uses defaults for parameters, and a user issues the stored procedure, but misspells the parameter name, Adaptive Server executes the store procedure using the default value and does not issue an error message. For example, if you create the following procedure: create procedure test @x int = 1 as select @x It returns the following: exec test @x = 2 go ---------------- 2 However, if you pass this stored procedure an incorrect parameter, it returns an incorrect result set, but does not issue a error message: exec test @z = 4 go ----------- 1 (1 row affected) (return status = 0) NULL as the default parameter In the create procedure statement, you can declare null as the default value for individual parameters: create procedure procedure_name @param datatype [ = null ] [, @param datatype [ = null ]]... In this case, if the user does not supply a parameter, Adaptive Server executes the stored procedure without displaying an error message. CHAPTER 15 Using Stored Procedures Transact-SQL User’s Guide 501 The procedure definition can specify an action be taken if the user does not give a parameter, by checking to see that the parameter’s value is null. Here is an example: create procedure showind3 @table varchar(30) = null as if @table is null print "Please give a table name." else select table_name = sysobjects.name, index_name = sysindexes.name, index_id = indid from sysindexes, sysobjects where sysobjects.name = @table and sysobjects.id = sysindexes.id If the user does not give a parameter, Adaptive Server prints the message from the procedure on the screen. For other examples of setting the default to null, examine the source text of system procedures using sp_helptext. Wildcard characters in the default parameter The default can include the wildcard characters (%, _, [] , and [^]) if the procedure uses the parameter with the like keyword. For example, you can modify showind to display information about the system tables if the user does not supply a parameter, like this: create procedure showind4 @table varchar(30) = "sys%" as select table_name = sysobjects.name, index_name = sysindexes.name, index_id = indid from sysindexes, sysobjects where sysobjects.name like @table and sysobjects.id = sysindexes.id Using more than one parameter Here is a variant of au_info that uses defaults with wildcard characters for both parameters: create proc au_info2 @lastname varchar(30) = "D%", Creating and executing stored procedures 502 Adaptive Server Enterprise @firstname varchar(18) = "%" as select au_lname, au_fname, title, pub_name from authors, titles, publishers, titleauthor where au_fname like @firstname and au_lname like @lastname and authors.au_id = titleauthor.au_id and titles.title_id = titleauthor.title_id and titles.pub_id = publishers.pub_id If you execute au_info2 with no parameters, all the authors with last names beginning with “D” are displayed: au_info2 au_lname au_fname title pub_name -------- ------- ------------------------- ------------- Dull Ann Secrets of Silicon Valley Algodata Infosystems DeFrance Michel The Gourmet Microwave Binnet & Hardley (2 rows affected) If defaults are available for parameters, parameters can be omitted at execution, beginning with the last parameter. You cannot skip a parameter unless NULL is its supplied default. Note If you supply parameters in the form @parameter = value, you can supply parameters in any order. You can also omit a parameter for which a default has been supplied. If you supply one value in the form @parameter = value, then supply all subsequent parameters this way. As an example of omitting the second parameter when defaults for two parameters have been defined, you can find the books and publishers for all authors with the last name “Ringer” like this: au_info2 Ringer au_lname au_fname title Pub_name -------- -------- --------------------- ------------ Ringer Anne The Gourmet Microwave Binnet & Hardley Ringer Anne Is Anger the Enemy? New Age Books Ringer Albert Is Anger the Enemy? New Age Books Ringer Albert Life Without Fear New Age Books (4 rows affected) If a user executes a stored procedure and specifies more parameters than the number of parameters expected by the procedure, Adaptive Server ignores the extra parameters. CHAPTER 15 Using Stored Procedures Transact-SQL User’s Guide 503 Remember that SQL is a free-form language. There are no rules about the number of words you can put on a line or where you must break a line. If you issue a stored procedure followed by a command, Adaptive Server attempts to execute the procedure and then the command. For example, if you issue: sp_help checkpoint Adaptive Server returns the output from sp_help and runs the checkpoint command. Using delimited identifiers for procedure parameters can produce unintended results. Procedure groups The optional semicolon and integer number after the name of the procedure in the create procedure and execute statements allow you to group procedures of the same name so that they can be dropped together with a single drop procedure statement. Procedures used in the same application are often grouped this way. For example, you might create a series of procedures called orders;1, orders;2, and so on. The following statement would drop the entire group: drop proc orders Once procedures have been grouped by appending a semicolon and number to their names, they cannot be dropped individually. For example, the following statement is not allowed: drop proc orders;2 To run Adaptive Server in the evaluated configuration, you must prohibit grouping of procedures. This prohibition ensures that every stored procedure has a unique object identifier and can be dropped individually. To disallow procedure grouping, a System Security Officer must reset the allow procedure grouping configuration parameter. For information, see the System Administration Guide. Using with recompile in create procedure In the create procedure statement, the optional clause with recompile comes just before the SQL statements. It instructs Adaptive Server not to save a plan for this procedure. A new plan is created each time the procedure is executed. Creating and executing stored procedures 504 Adaptive Server Enterprise In the absence of with recompile, Adaptive Server stores the execution plan that it created. Usually, this execution plan is satisfactory. However, a change in the data or parameter values supplied for subsequent executions may cause Adaptive Server to create an execution plan that is different from the one it created when the procedure was first executed. In such situations, Adaptive Server needs a new execution plan. Use with recompile in a create procedure statement when you think you need a new plan. See the Reference Manual for more information. Using with recompile in execute In the execute statement, the optional clause with recompile comes after any parameters. It instructs Adaptive Server to compile a new plan, which is used for subsequent executions. Use with recompile when you execute a procedure if your data has changed a great deal, or if the parameter you are supplying is atypical—that is, if you have reason to believe that the plan stored with the procedure might not be optimal for this execution of it. Note Using execute procedure with recompile many times can adversely affect the procedure cache performance. Since a new plan is generated every time you use with recompile, a useful performance plan may age out of the cache if there is insufficient space for new plans. Note If you use select * in your create procedure statement, the procedure, even if you use the with recompile option to execute, does not pick up any new columns added to the table. You must drop the procedure and re-create it. Nesting procedures within procedures Nesting occurs when one stored procedure or trigger calls another. The nesting level is incremented when the called procedure or trigger begins execution and it is decremented when the called procedure or trigger completes execution. Exceeding the maximum of 16 levels of nesting causes the procedure to fail. The current nesting level is stored in the @@nestlevel global variable. CHAPTER 15 Using Stored Procedures Transact-SQL User’s Guide 505 You can call another procedure by name or by a variable name in place of the actual procedure name. For example: create procedure test1 @proc_name varchar(30) as exec @proc_name Using temporary tables in stored procedures You can create and use temporary tables in a stored procedure, but the temporary table exists only for the duration of the stored procedure that creates it. When the procedure completes, Adaptive Server automatically drops the temporary table. A single procedure can: • Create a temporary table • Insert, update, or delete data • Run queries on the temporary table • Call other procedures that reference the temporary table Since the temporary table must exist to create procedures that reference it, here are the steps to follow: 1 Create the temporary table using a create table statement or a select into statement. For example: create table #tempstores (stor_id char(4), amount money) 2 Create the procedures that access the temporary table (but not the one that creates it). create procedure inv_amounts as select stor_id, "Total Due" = sum(amount) from #tempstores group by stor_id 3 Drop the temporary table: drop table #tempstores 4 Create the procedure that creates the table and calls the procedures created in step 2: create procedure inv_proc as create table #tempstores (stor_id char(4), amount money)Creating and executing stored procedures 506 Adaptive Server Enterprise When you run the inv_proc procedure, it creates the table, but it only exists during the procedure’s execution. Try inserting values into the #tempstores table or running the inv_amounts procedure: insert #tempstores select stor_id, sum(qty*(100-discount)/100*price) from salesdetail, titles where salesdetail.title_id = titles.title_id group by stor_id, salesdetail.title_id exec inv_amounts You cannot, because the #tempstores table no longer exists. You can also create temporary tables without the # prefix, using create table tempdb..tablename... from inside a stored procedure. These tables do not disappear when the procedure completes, so they can be referenced by independent procedures. Follow the above steps to create these tables. Setting options in stored procedures You can use some of the set command options inside a stored procedure. The set option remains in effect during the execution of the procedure and most options revert to the former setting at the close of the procedure. Only the dateformat, datefirst, language, and role options do not revert to their former settings. However, if you use a set option (such as identity_insert) that requires the user to be the object owner, a user who is not the object owner cannot execute the stored procedure. Arguments for stored procedures The maximum number of arguments for stored procedures is 2048. However, you may notice a performance degradation if you execute procedures with large numbers of arguments, because the query processing engine must process all the arguments and copy argument values to and from memory. Sybase recommends that you first test any stored procedures you write that include large numbers of arguments before you implement them in a production environment.CHAPTER 15 Using Stored Procedures Transact-SQL User’s Guide 507 Length of expressions, variables, and SP arguments The maximum size for expressions, variables, and arguments passed to stored procedures is 16384 (16K) bytes, for any page size. This can be either character or binary data. You can insert variables and literals up to this maximum size into text columns without using the writetext command. When you upgraded Adaptive Server and the prior version used a lower maximum length: Earlier versions of Adaptive Server had a maximum size of 255 bytes for expressions, variables, and arguments for stored procedures. Any scripts or stored procedures that you wrote for earlier versions of Adaptive Server that used this old maximum may now return larger string values because of the larger maximum page sizes. Because of the larger value, Adaptive Server may truncate the string, or the string may cause overflow if it was stored in another variable or inserted into a column or string. If columns of existing tables are modified to increase the length of character columns, you must change any stored procedures that operate data on these columns to reflect this new length. select datalength(replicate(“x”, 500)), datalength(“abcdefgh....255 byte long string..” + “xxyyzz ... another 255 byte long string”) ----------- ----------- 255 255 After creating a stored procedure After you create a stored procedure, the source text describing the procedure is stored in the text column of the syscomments system table. Do not remove this information from syscomments; doing so can cause problems for future upgrades of Adaptive Server. Instead, encrypt the text in syscomments by using sp_hidetext, described in the Reference Manual. For more information, see “Compiled objects” on page 4.Creating and executing stored procedures 508 Adaptive Server Enterprise Executing stored procedures You can execute stored procedures after a time delay or remotely. Executing procedures after a time delay The waitfor command delays execution of a stored procedure at a specified time or until a specified amount of time has passed. For example, to execute the procedure testproc in half an hour: begin waitfor delay "0:30:00" exec testproc end After issuing the waitfor command, you cannot use that connection to Adaptive Server until the specified time or event occurs. Executing procedures remotely You can execute procedures on a remote Adaptive Server from your local Adaptive Server. Once both servers are properly configured, you can execute any procedure on the remote Adaptive Server simply by using the server name as part of the identifier. For example, to execute a procedure named remoteproc on a server named GATEWAY: exec gateway.remotedb.dbo.remoteproc See the System Administration Guide for information on how to configure your local and remote Adaptive Servers for remote execution of procedures. You can pass one or more values as parameters to a remote procedure from the batch or procedure that contains the execute statement for the remote procedure. Results from the remote Adaptive Server appear on your local terminal.CHAPTER 15 Using Stored Procedures Transact-SQL User’s Guide 509 The return status from procedures can be used to capture and transmit information messages about the execution status of your procedures. For more information, see “Return status” on page 510. Warning! If Component Integration Services is not enabled, Adaptive Server does not treat remote procedure calls (RPCs) as part of a transaction. Therefore, if you execute an RPC as part of a transaction, and then roll back the transaction, Adaptive Server does not roll back any changes made by the RPC. When Component Integration Services is enabled, use set transactional rpc and set cis rpc handling to use transactional RPCs. For more information on the transactional rpc and cis rpc handling options, see the set command in the Reference Manual. Returning information from stored procedures Stored procedures can return the following types of information: • Return status – indicates whether or not the stored procedure completed successfully. • proc role function – checks whether the procedure was executed by a user with sa_role, sso_role, or ss_oper privileges. • Return parameters – report the parameter values back to the caller, who can then use conditional statements to check the returned value. Return status and return parameters allow you to modularize your stored procedures. A set of SQL statements that are used by several stored procedures can be created as a single procedure that returns its execution status or the values of its parameters to the calling procedure. For example, many Adaptive Server system procedures execute a procedure that verifies that certain parameters are valid identifiers. Remote procedure calls, which are stored procedures that run on a remote Adaptive Server, also return both kinds of information. All the examples below can be executed remotely if the syntax of the execute statement includes the server, database, and owner names, as well as the procedure name. Returning information from stored procedures 510 Adaptive Server Enterprise Return status Stored procedures report a return status that indicates whether or not they completed successfully, and if they did not, the reasons for failure. This value can be stored in a variable when a procedure is called, and used in future Transact-SQL statements. Adaptive Server-defined return status values for failure range from -1 through -99; users can define their own return status values outside this range. Here is an example of a batch that uses the form of the execute statement that returns the status: declare @status int execute @status = byroyalty 50 select @status The execution status of the byroyalty procedure is stored in the variable @status. “50” is the supplied parameter, based on the royaltyper column of the titleauthor table. This example prints the value with a select statement; later examples use this return value in conditional clauses. Reserved return status values Adaptive Server reserves 0, to indicate a successful return, and negative values from -1 through -99, to indicate the reasons for failure. Numbers 0 and -1 through -14 are currently used in version 12, as shown in Table 15-1:CHAPTER 15 Using Stored Procedures Transact-SQL User’s Guide 511 Table 15-1: Reserved return status values Values -15 through -99 are reserved for future use by Adaptive Server. If more than one error occurs during execution, the status with the highest absolute value is returned. User-generated return values You can generate your own return values in stored procedures by adding a parameter to the return statement. You can use any integer outside the 0 through -99 range. The following example returns 1 when a book has a valid contract and returns 2 in all other cases: create proc checkcontract @titleid tid as if (select contract from titles where title_id = @titleid) = 1 return 1 else return 2 For example: checkcontract MC2222 (return status = 1) Value Meaning 0 Procedure executed without error -1 Missing object -2 Datatype error -3 Process was chosen as deadlock victim -4 Permission error -5 Syntax error -6 Miscellaneous user error -7 Resource error, such as out of space -8 Non-fatal internal problem -9 System limit was reached -10 Fatal internal inconsistency -11 Fatal internal inconsistency -12 Table or index is corrupt -13 Database is corrupt -14 Hardware error Returning information from stored procedures 512 Adaptive Server Enterprise The following stored procedure calls checkcontract, and uses conditional clauses to check the return status: create proc get_au_stat @titleid tid as declare @retvalue int execute @retvalue = checkcontract @titleid if (@retvalue = 1) print "Contract is valid." else print "There is not a valid contract." Here are the results when you execute get_au_stat with the title_id of a book with a valid contract: get_au_stat MC2222 Contract is valid Checking roles in procedures If a stored procedure performs system administration or security-related tasks, you may want to ensure that only users who have been granted a specific role can execute it. The proc_role function allows you to check roles when the procedure is executed. It returns 1 if the user possesses the specified role. The role names are sa_role, sso_role, and oper_role. Here is an example using proc_role in the stored procedure test_proc to require the invoker to be a System Administrator: create proc test_proc as if (proc_role("sa_role") = 0) begin print "You do not have the right role." return -1 end else print "You have SA role." return 0 For example: test_proc You have SA role.CHAPTER 15 Using Stored Procedures Transact-SQL User’s Guide 513 Return parameters Another way that stored procedures can return information to the caller is through return parameters. The caller can then use conditional statements to check the returned value. When both a create procedure statement and an execute statement include the output option with a parameter name, the procedure returns a value to the caller. The caller can be a SQL batch or another stored procedure. The value returned can be used in additional statements in the batch or calling procedure. When return parameters are used in an execute statement that is part of a batch, the return values are printed with a heading before subsequent statements in the batch are executed. This stored procedure performs multiplication on two integers (the third integer, @result, is defined as an output parameter): create procedure mathtutor @mult1 int, @mult2 int, @result int output as select @result = @mult1 * @mult2 To use mathtutor to figure a multiplication problem, you must declare the @result variable and include it in the execute statement. Adding the output keyword to the execute statement displays the value of the return parameters. declare @result int exec mathtutor 5, 6, @result output (return status = 0) Return parameters: ----------- 30 If you wanted to guess at the answer and execute this procedure by providing three integers, you would not see the results of the multiplication. The select statement in the procedure assigns values, but does not print: mathtutor 5, 6, 32 (return status = 0) The value for the output parameter must be passed as a variable, not as a constant. This example declares the @guess variable to store the value to pass to mathtutor for use in @result. Adaptive Server prints the return parameters: declare @guess int select @guess = 32 exec mathtutor 5, 6, Returning information from stored procedures 514 Adaptive Server Enterprise @result = @guess output (1 row affected) (return status = 0) Return parameters: @result ----------- 30 The value of the return parameter is always reported, whether or not its value has changed. Note that: • In the example above, the output parameter @result must be passed as “@parameter = @variable”. If it were not the last parameter passed, subsequent parameters would have to be passed as “@parameter = value”. • @result does not have to be declared in the calling batch; it is the name of a parameter to be passed to mathtutor. • Although the changed value of @result is returned to the caller in the variable assigned in the execute statement, in this case @guess, it is displayed under its own heading, @result. To use the initial value of @guess in conditional clauses after the execute statement, you must store it in another variable name during the procedure call. The following example illustrates the last two bulleted items, above, by using @store to hold the value of the variable during the execution of the stored procedure, and by using the “new” returned value of @guess in conditional clauses: declare @guess int declare @store int select @guess = 32 select @store = @guess execute mathtutor 5, 6, @result = @guess output select Your_answer = @store, Right_answer = @guess if @guess = @store print "Bingo!" else print "Wrong, wrong, wrong!" (1 row affected) (1 row affected) (return status = 0) @result CHAPTER 15 Using Stored Procedures Transact-SQL User’s Guide 515 ----------- 30 Your_answer Right_answer ----------- ------------ 32 30 Wrong, wrong, wrong! This stored procedure checks to determine whether new book sales would cause an author’s royalty percentage to change (the @pc parameter is defined as an output parameter): create proc roy_check @title tid, @newsales int, @pc int output as declare @newtotal int select @newtotal = (select titles.total_sales + @newsales from titles where title_id = @title) select @pc = royalty from roysched where @newtotal >= roysched.lorange and @newtotal < roysched.hirange and roysched.title_id = @title The following SQL batch calls the roy_check after assigning a value to the percent variable. The return parameters are printed before the next statement in the batch is executed: declare @percent int select @percent = 10 execute roy_check "BU1032", 1050, @pc = @percent output select Percent = @percent go (1 row affected) (return status = 0) @pc ----------- 12 Percent ----------- 12 (1 row affected) The following stored procedure calls roy_check and uses the return value for percent in a conditional clause: Returning information from stored procedures 516 Adaptive Server Enterprise create proc newsales @title tid, @newsales int as declare @percent int declare @stor_pc int select @percent = (select royalty from roysched, titles where roysched.title_id = @title and total_sales >= roysched.lorange and total_sales < roysched.hirange and roysched.title_id = titles.title_id) select @stor_pc = @percent execute roy_check @title, @newsales, @pc = @percent output if @stor_pc != @percent begin print "Royalty is changed." select Percent = @percent end else print "Royalty is the same." If you execute this stored procedure with the same parameters used in the earlier batch, you see: execute newsales "BU1032", 1050 Royalty is changed Percent ----------- 12 (1 row affected, return status = 0) In the two preceding examples that call roy_check, @pc is the parameter that is passed to roy_check, and @percent is the variable containing the output. When newsales executes roy_check, the value returned in @percent may change, depending on the other parameters that are passed. To compare the returned value of percent with the initial value of @pc, you must store the initial value in another variable. The preceding example saved the value in stor_pc. Passing values in parameters To pass values in the parameters use this format: @parameter = @variableCHAPTER 15 Using Stored Procedures Transact-SQL User’s Guide 517 You cannot pass constants; there must be a variable name to “receive” the return value. The parameters can be of any Adaptive Server datatype except text or image. Note If the stored procedure requires several parameters, either pass the return value parameter last in the execute statement or pass all subsequent parameters in the form @parameter = value. The output keyword A stored procedure can return several values; each must be defined as an output variable in the stored procedure and in the calling statements. The output keyword can be abbreviated to out. exec myproc @a = @myvara out, @b = @myvarb out If you specify output while you are executing a procedure, and the parameter is not defined using output in the stored procedure, you get an error message. It is not an error to call a procedure that includes return value specifications without requesting the return values with output. However, you will not get the return values. The stored procedure writer has control over the information users can access, and users have control over their variables. Restrictions associated with stored procedures Here are some additional restrictions on creating stored procedures: • You cannot combine create procedure statements with other statements in the same batch. • The create procedure definition itself can include any number and kind of SQL statements, except use and these create statements: • create view • create default • create rule • create trigger • create procedureRestrictions associated with stored procedures 518 Adaptive Server Enterprise • You can create other database objects within a procedure. You can reference an object you created in the same procedure, as long as you create it before you reference it. The create statement for the object must come first in the actual order of the statements within the procedure. • Within a stored procedure, you cannot create an object, drop it, and then create a new object with the same name. • Adaptive Server creates the objects defined in a stored procedure when the procedure is executed, not when it is compiled. • If you execute a procedure that calls another procedure, the called procedure can access objects created by the first procedure. • You can reference temporary tables within a procedure. • If you create a temporary table with the #prefix inside a procedure, the temporary table exists only for purposes of the procedure—it disappears when you exit the procedure. Temporary tables created using create table tempdb..tablename do not disappear unless you explicitly drop them. • The maximum number of parameters in a stored procedure is 255. • The maximum number of local and global variables in a procedure is limited only by available memory. Qualifying names inside procedures Inside a stored procedure, object names used with create table and dbcc must be qualified with the object owner’s name, if other users are to use the stored procedure. Object names used with other statements, like select and insert, inside a stored procedure need not be qualified because the names are resolved when the procedure is compiled. For example, user “mary”, who owns table marytab, should qualify the name of her table when it is used with select or insert if she wants other users to execute the procedure in which the table is used. The reason for this rule is that object names are resolved when the procedure is run. If marytab is not qualified, and user “john” tries to execute the procedure, Adaptive Server looks for a table called marytab owned by the owner of the procedure (“john” in this case) or by the Database Owner if the user table (“marytab” in this case) does not exist. CHAPTER 15 Using Stored Procedures Transact-SQL User’s Guide 519 Renaming stored procedures Use sp_rename to rename stored procedures. Its syntax is: sp_rename objname, newname For example, to rename showall to countall: sp_rename showall, countall The new name must follow the rules for identifiers. You can change the name only of stored procedures that you own. The Database Owner can change the name of any user’s stored procedure. The stored procedure must be in the current database. Renaming objects referenced by procedures You must drop and re-create a procedure if you rename any of the objects it references. A stored procedure that references a table or view whose name has been changed may seem to work fine for a while. In fact, it works only until Adaptive Server recompiles it. Recompilation takes place for many reasons and without notification to the user. Use sp_depends to get a report of the objects referenced by a procedure. Using stored procedures as security mechanisms You can use stored procedures as security mechanisms to control access to information in tables and to control the ability to perform data modification. For example, you can deny other users permission to use the select command on a table that you own and create a stored procedure that allows them to see only certain rows or certain columns. You can also use stored procedures to limit update, delete, or insert statements. The person who owns the stored procedure must own the table or view used in the procedure. Not even a System Administrator can create a stored procedure to perform operations on another user’s tables, if the System Administrator has not been granted permissions on those tables. For information about granting and revoking permissions of stored procedures and other database objects, see the System Administration Guide.Dropping stored procedures 520 Adaptive Server Enterprise Dropping stored procedures Use drop procedure to remove stored procedures. Its syntax is: drop proc[edure] [owner.]procedure_name [, [owner.]procedure_name] ... If a stored procedure that was dropped is called by another stored procedure, Adaptive Server displays an error message. However, if a new procedure of the same name is defined to replace the one that was dropped, other procedures that reference the original procedure can call it successfully. A procedure group, that is, more than one procedure with the same name but with different numbered suffixes, can be dropped with a single drop procedure statement. Once procedures have been grouped, procedures within the group cannot be dropped individually. System procedures System procedures are: • Shortcuts for retrieving information from the system tables • Mechanisms for performing database administration and other tasks that involve updating system tables Most of the time, system tables are updated only through stored procedures. A System Administrator can allow direct updates of system tables by changing a configuration variable and issuing the reconfigure with override command. See the System Administration Guide for details. The names of system procedures begin with “sp_”. They are created by the installmaster script in the sybsystemprocs database during Adaptive Server installation. CHAPTER 15 Using Stored Procedures Transact-SQL User’s Guide 521 Executing system procedures You can run system procedures from any database. If a system procedure is executed from a database other than the sybsystemprocs database, any references to system tables are mapped to the database from which the procedure is being run. For example, if the Database Owner of pubs2 runs sp_adduser from pubs2, the new user is added to pubs2..sysusers. To run a system procedure in a specific database, either open that database with the use command and execute the procedure, or qualify the procedure name with the database name. When the parameter for a system procedure is an object name, and the object name is qualified by a database name or owner name, the entire name must be enclosed in single or double quotes. Permissions on system procedures Since system procedures are located in the sybsystemprocs database, their permissions are also set there. Some system procedures can be run only by Database Owners. These procedures ensure that the user executing the procedure is the owner of the database on which they are executed. Other system procedures can be executed by any user who has been granted execute permission on them, but this permission must be granted in the sybsystemprocs database. This situation has two consequences: • A user can have permission to execute a system procedure either in all databases or in none of them. • The owner of a user database cannot directly control permissions on the system procedures within his or her own database. Types of system procedures System procedures can be grouped by function, such as auditing, security administration, data definition, and so on. The following sections list the types of system procedures. For complete information about the system procedures, see the Reference Manual. System procedures 522 Adaptive Server Enterprise System procedures for auditing These system procedures are used for: • Controlling audit settings • Creating and managing the tables which hold the audit queue The procedures in this category are: For more information on auditing, see the Security Administration Guide. System procedures used for security administration These system procedures are used for: • Adding, dropping, and reporting on logins on Adaptive Server • Adding, dropping, and reporting on users, groups, roles, and aliases in a database • Changing passwords and default databases • Adding, dropping, and reporting on remote servers that can access the current Adaptive Server • Adding the names of users from remote servers who can access the current Adaptive Server sp_addauditrecord sp_addaudittable sp_audit sp_displayauditCHAPTER 15 Using Stored Procedures Transact-SQL User’s Guide 523 The procedures in this category are: Additional system procedures are available for Windows NT. The procedures in this category are: System procedures used for remote servers These system procedures are used for: • Adding, dropping and reporting on remote servers that can access the current Adaptive Server • Adding the names of users from remote servers who can access the current Adaptive Server The procedures in this category are: Additional system procedures are available if you have Component Integration Services installed. The procedures in this category are: System procedures for managing databases These system procedures are used for: • Changing the owner of a database • Displaying and changing database options sp_activeroles sp_changegroup sp_droplogin sp_locklogin sp_addalias sp_displaylogin sp_dropuser sp_modifylogin sp_addgroup sp_displayroles sp_helpgroup sp_password sp_addlogin sp_dropalias sp_helprotect sp_role sp_adduser sp_dropgroup sp_helpuser sp_grantlogin sp_logininfo sp_revokelogin sp_loginconfig sp_processmail sp_addremotelogin sp_dropserver sp_remoteoption sp_addserver sp_helpremotelogin sp_serveroption sp_dropremotelogin sp_helpserver sp_addexternlogin sp_dropexternlogin sp_passthru sp_addobjectdef sp_dropobjectdef sp_remotesql sp_autoconnect sp_helpexternlogin sp_defaultloc sp_helpobjectdefSystem procedures 524 Adaptive Server Enterprise The procedures in this category are: System procedures used for data definition and database objects These system procedures are used for: • Binding and unbinding rules and defaults • Adding, dropping, and reporting on primary keys, foreign keys, and common keys • Adding, dropping, and reporting on user-defined datatypes • Renaming database objects and user-defined datatypes • Re-optimizing stored procedures and triggers • Binding and unbinding objects to data caches • Reporting on database objects, user-defined datatypes, dependencies among database objects, databases, indexes, and space used by tables and indexes • Getting help on command syntax The procedures in this category are sp_changedbowner sp_dbremap sp_renamedb sp_dboption sp_helpdb sp_addextendedproc sp_dropkey sp_helptext sp_addtype sp_droptype sp_hidetext sp_bindcache sp_estspace sp_poolconfig sp_bindefault sp_foreignkey sp_primarykey sp_bindrule sp_freedll sp_procxmode sp_cacheconfig sp_help sp_recompile sp_cachestrategy sp_helpartition sp_rename sp_chgattribute sp_helpcache sp_spaceused sp_checksource sp_helpconstraint sp_unbindcache sp_commonkey sp_helpextendedproc sp_unbindcache_all sp_cursorinfo sp_helpindex sp_unbindefault sp_depends sp_helpjoins sp_unbindrule sp_dropextendedproc sp_helpkeyCHAPTER 15 Using Stored Procedures Transact-SQL User’s Guide 525 System procedures used for user-defined messages These system procedures are used for: • Adding user-defined messages to the sysusermessages table in a user database • Dropping user-defined messages from sysusermessages • Retrieving messages from either sysusermessages or sysmessages in the master database for use in print and raiserror statements The procedures in this category are: System procedures for languages These system procedures are used for: • Managing character sets • Adding and dropping alternate languages The procedures in this category are: System procedures used for device management These system procedures are used for: • Adding, dropping, and reporting on database and dump devices • Adding, dropping, and extending database segments The procedures in this category are: sp_addmessage sp_bindmsg sp_getmessage sp_altermessage sp_dropmessage sp_unbindmsg sp_addlanguage sp_helplanguage sp_setlangalias sp_checknames sp_helpsort sp_droplanguage sp_indsuspect sp_addsegment sp_dropsegment sp_helpsegment sp_addumpdevice sp_extendsegment sp_logdevice sp_diskdefault sp_helpdevice sp_logiosize sp_dropdevice sp_helplog sp_placeobjectSystem procedures 526 Adaptive Server Enterprise System procedures used for backup and recovery These system procedures are used for: • Creating and managing thresholds • Displaying and setting recovery isolation mode • Communicating with Backup Server™ The procedures in this category are: System procedures used for configuration and tuning These system procedures are used for: • Changing and reporting on configuration parameters • Reporting on system usage • Reporting performance behavior • Monitoring Adaptive Server activity The procedures in this category are: System procedures used for system administration These system procedures are used for: • Reporting on locks and the users currently running processes • Altering the lock promotion thresholds of a table or database • Creating and reporting on resource limits and time ranges • Creating and reporting on execution classes and engine groups • Planning the layout of the dbccdb database sp_addthreshold sp_helpthreshold sp_setsuspect_granularity sp_dropthreshold sp_listsuspect_db sp_setsuspect_threshold sp_forceonline_db sp_listsuspect_page sp_thresholdaction sp_forceonline_page sp_modifythreshold sp_volchanged sp_clearstats sp_monitor sp_configure sp_monitorconfig sp_countmetadata sp_reportstats sp_displaylevel sp_showplan sp_helpconfig sp_sysmonCHAPTER 15 Using Stored Procedures Transact-SQL User’s Guide 527 The procedures in this category are: See the System Administration Guide for more information about the system procedures that accomplish these administrative tasks. System procedures for upgrade These system procedures are used for: • Checking for reserved words • Remapping objects • Checking the query processing mode of an object The procedures in this category are: Other Sybase-supplied procedures Sybase provides catalog stored procedures, system extended stored procedures (system ESPs) and dbcc procedures. Catalog stored procedures Catalog stored procedures are system procedures which retrieve information from the system tables in tabular form. The catalog stored procedures are: sp_addengine sp_drop_resource_limit sp_setpsexe sp_addexeclass sp_drop_time_range sp_showcontrolinfo sp_add_resource_limit sp_familylock sp_showexeclass sp_add_time_range sp_help_resource_limit sp_showpsexe sp_bindexeclass sp_lock sp_unbindexeclass sp_clearpsexe sp_modify_resource_limit sp_setpsexe sp_dropexeclass sp_modify_time_range sp_who sp_dropengine sp_setpglockpromote sp_dropglockpromote sp_plan_dbccdb sp_checkreswords sp_remap sp_column_privileges sp_pkeys sp_stored_procedures sp_columns sp_server_info sp_table_privileges sp_databases sp_special_columns sp_tables sp_datatype_info sp_sproc_columnsGetting information about stored procedures 528 Adaptive Server Enterprise System extended stored procedures Extended stored procedures (ESPs) call procedural language functions from Adaptive Server. The system extended stored procedures, created by installmaster at installation, are located in the sybsystemprocs database and are owned by the System Administrator. They can be run from any database and their names begin with “xp_”. The system extended stored procedures are: See Chapter 16, “Using Extended Stored Procedures,” for more information on creating and using ESPs. dbcc procedures The dbcc procedures, created by installdbccdb, are stored procedures for generating reports on information created by dbcc checkstorage. These procedures reside in the dbccdb database or in the alternate database, dbccalt. The dbcc procedures are: Getting information about stored procedures Several system procedures provide information from the system tables about stored procedures. System procedures are briefly discussed in “System procedures” on page 520. For complete information about system procedures, see the Reference Manual. sp_fkeys sp_statistics xp_cmdshell xp_findnextmsg xp_sendmai xp_deletemail xp_logevent xp_startmai xp_enumgroups xp_readmail xp_stopmai sp_dbcc_alterws sp_dbcc_differentialreport sp_dbcc_statisticsreport sp_dbcc_configreport sp_dbcc_evaluatedb sp_dbcc_summaryreport sp_dbcc_createws sp_dbcc_faultreport sp_dbcc_updateconfig sp_dbcc_deletedb sp_dbcc_fullreport sp_dbcc_deletehistory sp_dbcc_runcheck CHAPTER 15 Using Stored Procedures Transact-SQL User’s Guide 529 Getting a report with sp_help You can get a report on a stored procedure using sp_help. For example, you can get information on the stored procedure byroyalty, which is part of the pubs2 database, like this: sp_help byroyalty Name Owner type -------- ------ ---------------- byroyalty dbo stored procedure Data_located_on_segment When_created --------------------------- -------------------- not applicable Jul 10, 1997 4:57PM Parameter_name Type Length Prec Scale Param_order -------------- ------ ------ ---- ----- ----------- @percentage int 4 NULL NULL 1 (return status = 0) You can get help on a system procedure by executing sp_help when using the sybsystemprocs database. Viewing the source text of a procedure with sp_helptext To display the source text of the create procedure statement, execute sp_helptext: sp_helptext byroyalty # Lines of Text --------------- 1 (1 row affected) text --------------------------------------------------- create procedure byroyalty @percentage int as select au_id from titleauthor where titleauthor.royaltyper = @percentage (1 row affected, return status = 0)Getting information about stored procedures 530 Adaptive Server Enterprise You can view the source text of a system procedure by executing sp_helptext when using the sybsystemprocs database. If the source text of a stored procedure was encrypted using sp_hidetext, Adaptive Server displays a message advising you that the text is hidden. For information about hiding source text, see sp_hidetext in the Reference Manual. Identifying dependent objects with sp_depends sp_depends lists all the stored procedures that reference the object you specify or all the procedures that it is dependent upon. For example, this command lists all the objects referenced by the user-created stored procedure byroyalty: sp_depends byroyalty Things the object references in the current database. object type updated selected ---------------- ----------- --------- -------- dbo.titleauthor user table no no (return status = 0) The following statement uses sp_depends to list all the objects that reference the table titleauthor: sp_depends titleauthor Things inside the current database that reference the object. object type -------------- ------------------ dbo.byroyalty stored procedure dbo.titleview view (return status = 0) You must drop and re-create the procedure if any of its referenced objects have been renamed. Identifying permissions with sp_helprotect sp_helprotect reports permissions on a stored procedure (or any other database object). For example:CHAPTER 15 Using Stored Procedures Transact-SQL User’s Guide 531 sp_helprotect byroyalty grantor grantee type action object column grantable --------- --------- ---- --------- ------- ----- --------- dbo public Grant Execute byroyalty All FALSE (return status = 0)Getting information about stored procedures 532 Adaptive Server EnterpriseTransact-SQL User’s Guide 533 C H A P T E R 1 6 Using Extended Stored Procedures Extended stored procedures (ESPs) provide a mechanism for calling external procedural language functions from within Adaptive Server. Users invoke ESPs using the same syntax as they use for stored procedures. The difference is that an ESP executes procedural language code rather than Transact-SQL statements. This chapter discusses: Overview Extended stored procedures provide a way to dynamically load and execute external procedural language functions from within Adaptive Server. Each ESP is associated with a corresponding function, which is executed when the ESP is invoked from Adaptive Server. Topic Page Overview 533 Creating functions for ESPs 539 Registering ESPs 550 Removing ESPs 552 Executing ESPs 552 System ESPs 554 Getting information about ESPs 554 ESP exceptions and messages 555 Starting XP Server manually 556Overview 534 Adaptive Server Enterprise An ESP allows Adaptive Server to perform a task outside Adaptive Server in response to an event occurring within Adaptive Server. For example, you could create an ESP function to sell a security (a task performed outside Adaptive Server). This function is invoked in response to a trigger that is fired when the price of the security reaches a certain value. Or you could create an ESP function that sends an e-mail notification or a network-wide broadcast in response to an event occurring within the relational database system. For the purposes of ESPs, “a procedural language” is a programming language that is capable of calling a C language function and manipulating C language datatypes. After a function has been registered in a database as an ESP, it can be invoked just like a stored procedure from isql, from a trigger, from another stored procedure, or from a client application. ESPs can: • Take input parameters • Return a status value indicating success or failure and the reason for the failure • Return values of output parameters • Return result sets Adaptive Server supplies some system ESPs. For example, one system ESP, xp_cmdshell, executes an operating system command from within Adaptive Server. You can also write your own ESPs using a subset of the Open Server application programming interface (API). XP Server Extended stored procedures are implemented by an Open Server application called XP Server, which runs on the same machine as Adaptive Server. Adaptive Server and XP Server communicate through remote procedure calls (RPCs). Running ESPs in a separate process protects Adaptive Server from a failure resulting from faulty ESP code. The advantage of using ESPs instead of RPCs is that the ESP runs in Adaptive Server the same way a stored procedure runs; you do not need to have Open Server to run the ESP. XP Server is automatically installed when Adaptive Server is installed.CHAPTER 16 Using Extended Stored Procedures Transact-SQL User’s Guide 535 XP Server must be running for Adaptive Server to execute an ESP. Adaptive Server starts XP Server the first time an ESP is invoked and shuts down XP Server when Adaptive Server itself exits. On Windows NT, if the start mail session configuration parameter is set to 1, XP Server automatically starts when Adaptive Server starts. Dynamic Link Library Support The procedural functions that contain the ESP code are compiled and linked into dynamic link libraries (DLLs), which are loaded into XP Server memory in response to an ESP execution request. The library remains loaded unless one of the following occurs: • XP Server exits • The sp_freedll system procedure is invoked • The esp unload dll configuration parameter is set using sp_configure Open Server API Adaptive Server uses the Open Server API, which allows users to run the system ESPs provided with Adaptive Server. Users can also implement their own ESPs using the Open Server API. Table 16-1 lists the Open Server routines required for ESP development. For complete documentation of these routines, see the Open Server Server-Library/C Reference Manual.Overview 536 Adaptive Server Enterprise Table 16-1: Open Server routines for ESP support Example of creating and using ESPs After an ESP function has been written, compiled, and linked into a DLL, you can create an ESP for the function using the as external name clause of the create procedure command: create procedure procedure_name [parameter_list] as external name dll_name procedure_name is the name of the ESP, which must be the same as the name of its implementing function in the DLL. ESPs are database objects, and their names must follow the rules for identifiers. dll_name is the name of the DLL in which the implementing function is stored. The following statement creates an ESP named getmsgs, which is in msgs.dll. The getmsgs ESP takes no parameters. This example is for a Windows NT Adaptive Server: create procedure getmsgs as external name "msgs.dll" On a Solaris Adaptive Server, the statement is: create procedure getmsgs as external name "msgs.so" This reflects the Solaris naming conventions. Function Purpose srv_bind Describes and binds a program variable to a parameter. srv_descfmt Describes a parameter. srv_numparams Returns the number of parameters in the ESP client request. srv_senddone Sends results completion message. srv_sendinfo Sends messages. srv_sendstatus Sends status value. srv_xferdata Sends and receives parameters or data. srv_yield Suspends execution of the current thread and allows another thread to execute.CHAPTER 16 Using Extended Stored Procedures Transact-SQL User’s Guide 537 The next statement creates an ESP named getonemsg, which is also in msgs.dll. The getonemsg ESP takes a message number as a single parameter. create procedure getonemsg @msg int as external name "msgs.dll" The platform-specific naming conventions for the DLL extension are summarized in Table 16-2. Table 16-2: Naming conventions for DLL extensions When Adaptive Server creates an ESP, it stores the procedure’s name in the sysobjects system table, with an object type of “XP” and the name of the DLL containing the ESP’s function in the text column of the syscomments system table. Execute an ESP as if it were a user-defined stored procedure or system procedure. You can use the keyword execute and the name of the stored procedure, or just give the procedure’s name, as long as it is submitted to Adaptive Server by itself or is the first statement in a batch. For example, you can execute getmsgs in any of these ways: getmsgs execute getmsgs exec getmsgs You can execute getonemsg in any of these ways: getonemsg 20 getonemsg @msg=20 execute getonemsg 20 execute getonemsg @msg=20 exec getonemsg 20 exec getonemsg @msg=20 ESPs and Permissions You can grant and revoke permissions on an ESP as you would on a regular stored procedure. Platform DLL extension Digital UNIX .so HP 9000/800 HP-UX .sl Sun Solaris .so Windows NT .dllOverview 538 Adaptive Server Enterprise In addition to the normal Adaptive Server security, you can use the xp_cmdshell context configuration parameter to restrict execution permission of xp_cmdshell to users who have system administration privileges. Use this configuration parameter to prevent ordinary users from using xp_cmdshell to execute operating system commands that they would not have permission to execute directly from the command line. The behavior of the xp_cmdshell configuration parameter is platformspecific. By default, a user must have the sa_role to execute xp_cmdshell. To grant permission to other users to use xp_cmdshell, use the grant command. You can revoke the permission with revoke. The grant or revoke permission is applicable whether xp_cmdshell context is set to 0 or 1. ESPs and Performance Since both Adaptive Server and XP Server reside on the same machine, they can affect each other’s performance when XP Server is executing a function that consumes significant resources. You can use sp_configure to set two parameters, esp execution priority and esp unload dll, to control the impact of XP Server on Adaptive Server by setting priorities for ESP execution and by freeing XP Server memory. Setting Priority Use esp execution priority to set the priority of the XP Server thread high, so the Open Server scheduler runs it before other threads on its run queue, or low, so the scheduler runs XP Server only when there are no other threads to run. The default value of esp execution priority is 8, but you can set it anywhere from 0 to 15. See the discussion of multithread programming in the Open Server Server-Library/C Reference Manual for information about scheduling Open Server threads. Freeing Memory You can minimize the amount of memory XP Server uses by unloading a DLL from XP Server memory after the ESP request that loaded it terminates. To do so, set esp unload dll so that the DLLs are automatically unloaded when ESP execution finishes. If esp unload dll is not set, you can free DLLs explicitly by using sp_freedll.CHAPTER 16 Using Extended Stored Procedures Transact-SQL User’s Guide 539 You cannot unload DLLs that support system ESPs. Creating functions for ESPs There are no restrictions on the contents of a function that implements an ESP. The only requirement is that it be written in a procedural programming language capable of: • Calling a C language function • Manipulating C language datatypes • Linking with the Open Server API By using the Open Client API, an ESP function can send requests to Adaptive Server, either to the one from which it was originally invoked or to another one. An exception is that an ESP function should not call a C run-time signal routine on Windows NT. This can cause XP Server to fail, because Open Server does not support signal handling on Windows NT. Files for ESP Development The header files needed for ESP development are in $SYBASE/OCS- 12_0/include. To find these files in your source files, include the following in the source code: • ospublic.h • oserror.h The Open Server library is in $SYBASE/lib. The source for the sample program shown in “ESP function example” on page 541 is in $SYBASE/$SYBASE_ASE/sample/esp. Open Server data structures Three data structures are useful for writing ESP functions: • SRV_PROCCreating functions for ESPs 540 Adaptive Server Enterprise • CS_SERVERMSG • CS_DATAFMT SRV_PROC All ESP functions are coded to accept a single parameter, a pointer to a SRV_PROC structure. The SRV_PROC structure passes information between the function and its calling process. ESP developers cannot manipulate this structure directly. The ESP function passes the SRV_PROC pointer to Open Server routines that get parameter types and data and return output parameters, status codes, and result sets. CS_SERVERMSG Open Server uses the CS_SERVERMSG structure to send error messages to a client using the srv_sendinfo routine. See the Open Server-Library/C Reference Manual for information about CS_SERVERMSG. CS_DATAFMT Open Server uses the CS_DATAFMT structure to describe data values and program variables. Open Server return codes Open Server functions return a code of type CS_RETCODE. The most common CS_RETCODE values for ESP functions are: • CS_SUCCEED • CS_FAIL Outline of a simple ESP function An ESP function should have the following basic structure with regard to its interaction with the Open Server API: 1 Get the number of parameters.CHAPTER 16 Using Extended Stored Procedures Transact-SQL User’s Guide 541 2 Get the values of the input/output parameters and bind them to local variables. 3 Perform the processing using the input parameter values and store the results in local variables. 4 Initialize any output parameters with appropriate values, bind them with local variables, and transfer them to the client. 5 Use srv_sendinfo() to send the returned row to the client. 6 Use srv_sendstatus() to send the status to the client. 7 Use srv_senddone() to inform the client that the processing is done. 8 If there is an error condition, use srv_sendinfo() to send the error message to the client. See the Open Server Server-Library/C Reference Manual for documentation of the Open Server routines. Multithreading Since Open Server is currently non-preemptive, all ESPs running on the same server must yield to one another, using the Open Server srv_yield() routine to suspend their XP Server thread and allow another thread to execute. See the chapter on Multithread Programming in the Open Server ServerLibrary/C Reference Manual for more information. ESP function example xp_echo.c has an ESP that accepts a user-supplied input parameter and echoes it to the ESP client, which is the process invoking the ESP. This example includes the xp_message function, which sends messages and status, and the xp_echo function which processes the input parameter and performs the echoing. You can use this example as a template for building your own ESP functions. The source is in $SYBASE/$SYBASE_ASE/sample/esp. /* ** xp_echo.c ** ** Description: ** The following sample program is generic inCreating functions for ESPs 542 Adaptive Server Enterprise ** nature. It echoes an input string which is ** passed as the first parameter to the xp_echo ** ESP. This string is retrieved into a buffer ** and then sent back (echoed) to the ESP client. */ #include #include #include /* Required Open Server include files.*/ #include #include /* ** Constant defining the length of the buffer that receives the ** input string. All of the Adaptive Server parameters related ** to ESP may not exceed 255 char long. */ #define ECHO_BUF_LEN 255 /* ** Function: ** xp_message ** Purpose: Sends information, status and completion of the ** command to the server. ** Input: ** SRV_PROC * ** char * a message string. ** Output: ** void */ void xp_message ( SRV_PROC *srvproc, /* Pointer to Open Server thread control structure */ char *message_string /* Input message string */ ) { /* ** Declare a variable that will contain information ** about the message being sent to the SQL client. */ CS_SERVERMSG *errmsgp; /* ** Allocate memory for this variable. */ errmsgp = (CS_SERVERMSG *) malloc((CS_INT sizeof(CS_SERVERMSG)); if (errmsgp == NULL)CHAPTER 16 Using Extended Stored Procedures Transact-SQL User’s Guide 543 return; /* ** clean the structure */ */ memset(errmsgp,(CS_INT)0,(CS_INT) sizeof(CS_SERVERMSG)); /* ** Put you rnumber in as the message number. */ errmsgp->msgnumber = 25000; errmsgp->state = 0; /* **The message is fatal. */ errmsgp->severity = SRV_FATAL_SERVER; /* ** Let’s copy the string over. */ errmsgp->textlen = strlen(message_string); if (errmsgp->textlen >= CS_MAX_MSG ) return; strncpy(errmsgp->text, message_string, errmsgp->textlen); errmsgp->status = (CS_FIRST_CHUNK | CS_LAST_CHUNK); srv_sendinfo(srvproc, errmsgp, CS_TRAN_UNDEFINED); /* Send the status to the client. */ srv_sendstatus(srvproc, 1); /* ** A SRV_DONE_MORE instead of a SRV_DONE_FINAL must ** complete the result set of an Extended Stored ** Procedure. */ srv_senddone(srvproc, SRV_DONE_MORE, 0, 0); free(errmsgp); } /* ** Function: xp_echo ** Purpose: ** Given an input string, this string is echoed as an output ** string to the corresponding SQL (ESP) client. ** Input: ** SRV_PROC * ** Output ** SUCCESS or FAILURE */ CS_RETCODE xp_echo ( SRV_PROC *srvprocCreating functions for ESPs 544 Adaptive Server Enterprise ) { CS_INT paramnum; /* number of parameters */ CS_CHAR echo_str_buf[ECHO_BUF_LEN + 1]; /* buffer to hold input string */ CS_RETCODE result = CS_SUCCEED; CS_DATAFMT paramfmt; /* input/output param format */ CS_INT len; /* Length of input param */ CS_SMALLINT outlen; /* ** Get number of input parameters.*/ */ srv_numparams(srvproc, ¶mnum); /* ** Only one parameter is expected.*/ */ if (paramnum != 1) { /* ** Send a usage error message.*/ */ xp_message(srvproc, "Invalid number of parameters"); result = CS_FAIL; } else { /* ** Perform initializations. */ outlen = CS_GOODDATA; memset(¶mfmt, (CS_INT)0, (CS_INT)sizeof(CS_DATAFMT)); /* ** We are receiving data through an ESP as the ** first parameter. So describe this expected ** parameter. */ if ((result == CS_SUCCEED) && srv_descfmt(srvproc, CS_GET SRV_RPCDATA, 1, ¶mfmt) != CS_SUCCEED) { result = CS_FAIL; } /* ** Describe and bind the buffer to receive theCHAPTER 16 Using Extended Stored Procedures Transact-SQL User’s Guide 545 ** parameter. */ if ((result == CS_SUCCEED) && (srv_bind(srvproc, CS_GET, SRV_RPCDATA, 1, ¶mfmt,(CS_BYTE *) echo_str_buf, &len, &outlen) != CS_SUCCEED)) { result = CS_FAIL; } /* Receive the expected data.*/ if ((result == CS_SUCCEED) && srv_xferdata(srvproc,CS_GET,SRV_RPCDATA) != CS_SUCCEED) { result = CS_FAIL; } /* ** Now we have the input info and are ready to ** send the output info. */ if (result == CS_SUCCEED) { /* ** Perform initialization. */ if (len == 0) outlen = CS_NULLDATA; else outlen = CS_GOODDATA; memset(¶mfmt, (CS_INT)0, (CS_INT)sizeof(CS_DATAFMT)); strcpy(paramfmt.name, "xp_echo"); paramfmt.namelen = CS_NULLTERM; paramfmt.datatype = CS_CHAR_TYPE; paramfmt.format = CS_FMT_NULLTERM; paramfmt.maxlength = ECHO_BUF_LEN; paramfmt.locale = (CS_LOCALE *) NULL; paramfmt.status |= CS_CANBENULL; /* ** Describe the data being sent. */ if ((result == CS_SUCCEED) && srv_descfmt(srvproc, CS_SET, SRV_ROWDATA, 1, ¶mfmt) != CS_SUCCEED) {Creating functions for ESPs 546 Adaptive Server Enterprise result = CS_FAIL; } /* ** Describe and bind the buffer that ** contains the data to be sent. */ if ((result == CS_SUCCEED) && (srv_bind(srvproc, CS_SET, SRV_ROWDATA, 1, ¶mfmt, (CS_BYTE *) echo_str_buf, &len, &outlen) != CS_SUCCEED)) { result = CS_FAIL; } /* ** Send the actual data. */ if ((result == CS_SUCCEED) && srv_xferdata(srvproc, CS_SET, SRV_ROWDATA)!= CS_SUCCEED) { result = CS_FAIL; } } /* ** Indicate to the ESP client how the ** transaction was performed. */ if (result == CS_FAIL) srv_sendstatus(srvproc, 1); else srv_sendstatus(srvproc, 0); /* ** Send a count of the number of rows sent to ** the client. */ srv_senddone(srvproc,(SRV_DONE_COUNT | SRV_DONE_MORE), 0, 1); } return result; }CHAPTER 16 Using Extended Stored Procedures Transact-SQL User’s Guide 547 Building the DLL You can use any compiler that can produce the required DLL on your server platform. For general information about compiling and linking a function that uses the Open Server API, see the Open Client/Server Supplement. Search order for DLLs Windows NT searches for a DLL in the following order: 1 The directory from which the application was invoked 2 The current directory 3 The system directory (SYSTEM32) 4 Directories listed in the PATH environment variable UNIX searches for the library in the directories listed in the LD_LIBRARY_PATH environment variable (on Solaris and Digital UNIX) or SH_LIBRARY_PATH (on HP) in the order in which they are listed. If XP Server does not find the library for an ESP function in the search path, it attempts to load it from $SYBASE/DLL on Windows NT or $SYBASE/lib on other platforms. Absolute path names for the DLL are not supported. Sample makefile (UNIX) The following makefile, make.unix, was used to create the dynamically linked shared library for the xp_echo program on UNIX platforms. It generates a file named examples.so on Solaris and Digital UNIX and examples.sl on HP. The source is in $SYBASE/$SYBASE_ASE/sample/esp, so you can modify it for your own use. To build the example library using this makefile, enter: make /f make.unix # # This makefile creates a shared library. It needs the open # server header # files usually installed in $SYBASE/include directory. # This make file can be used for generating the template ESPs. # It references the following macros:Creating functions for ESPs 548 Adaptive Server Enterprise # # PROGRAM is the name of the shared library you may want to create. PROGRAM = example.so BINARY = $(PROGRAM) EXAMPLEDLL = $(PROGRAM) # Include path where ospublic.h etc reside. You may have them in # the standard places like /usr/lib etc. INCLUDEPATH = $(SYBASE)/include # Place where the shared library will be generated. DLLDIR = . RM = /usr/bin/rm ECHO = echo MODE = normal # Directory where the source code is kept. SRCDIR = . # Where the objects will be generated. OBJECTDIR = . OBJS = xp_echo.o CFLAGS = -I$(INCLUDEPATH) LDFLAGS = $(GLDFLAGS) -Bdynamic DLLLDFLAGS = -dy -G #================================================================ $(EXAMPLEDLL) : $(OBJS) -@$(RM) -f $(DLLDIR)/$(EXAMPLEDLL) -@$(ECHO) "Loading $(EXAMPLEDLL)" -@$(ECHO) " " -@$(ECHO) " MODE: $(MODE)" -@$(ECHO) " OBJS: $(OBJS)" -@$(ECHO) " DEBUGOBJS: $(DEBUGOBJS)" -@$(ECHO) " " cd $(OBJECTDIR); \ ld -o $(DLLDIR)/$(EXAMPLEDLL) $(DEBUGOBJS) $(DLLLDFLAGS) $(OBJS) -@$(ECHO) "$(EXAMPLEDLL) done" exit 0CHAPTER 16 Using Extended Stored Procedures Transact-SQL User’s Guide 549 #================================================================ $(OBJS) : $(SRCDIR)/xp_echo.c cd $(SRCDIR); \ $(CC) $(CFLAGS) -o $(OBJECTDIR)/$(OBJS) -c xp_echo.c Sample makefile (Windows NT) The following makefile, xp_echo.mak, was used to create the DLL for the xp_echo program on Windows NT using Microsoft Visual C++. It generates a file named xp_echo.dll. The source for the makefile is in $SYBASE\%SYBASE_ASE%\sample\esp, so you can modify it for your own use. To build the example DLL using this makefile, enter: nmake -f xp_echo.mak # Nmake macros for building Windows 32-Bit apps !include all: xp_echo.dll # Update the object file if necessary xp_echo.obj: xp_echo.c $(cc) $(cflags) $(cvars) $(cdebug) xp_echo.c # Update the xp_echo.dll if necessary xp_echo.dll: xp_echo.obj $(link) $(linkdebug) -def:xp_echo.def -out:xp_echo.dll \ xp_echo.obj shell32.lib libsrv.lib Sample definitions file The following file, xp_echo.def, must be in the same directory as xp_echo.mak. It lists every function to be used as an ESP function in the EXPORTS section. LIBRARY examples CODE PRELOAD MOVEABLE DISCARDABLE DATA PRELOAD SINGLE EXPORTS xp_echo . 1Registering ESPs 550 Adaptive Server Enterprise Registering ESPs Once you have created an ESP function and linked it into a DLL, register it as an ESP in a database. This lets the user execute the function as an ESP. Use either of these methods to register an ESP: • The Transact-SQL create procedure command • The sp_addextendedproc system procedure Using create procedure The create procedure syntax for creating an ESP is compatible with proposed ANSI SQL3 syntax: create procedure [owner.]procedure_name [[(]@parameter_name datatype [= default] [output] [, @parameter_name datatype [= default] [output]]...[)]] [with recompile] as external name dll_name The procedure_name is the name of the ESP as it is known in the database. It must be the same as the name of its supporting function. The parameter declarations are the same as for stored procedures, as described in Chapter 15, “Using Stored Procedures.” Adaptive Server ignores the with recompile clause if it is included in a create procedure command used to create an ESP. The dll_name is the name of the library containing the ESP’s supporting function. The dll_name can be specified as a name with no extension (for example, msgs) or a name with a platform-specific extension, such as msgs.dll on Windows NT or msgs.so on Solaris. In either case, the platform-specific extension is assumed to be part of the library’s actual file name. Since create procedure registers an ESP in a specific database, you should specify the database in which you are registering the ESP before invoking the command. From isql, specify the database with the use database command, if you are not already working in the target database.CHAPTER 16 Using Extended Stored Procedures Transact-SQL User’s Guide 551 The following statements register an ESP supported by the xp_echo routine described in the example in “ESP function example” on page 541, assuming that the function is compiled in a DLL named examples.dll. The ESP is registered in the pubs2 database. use pubs2 create procedure xp_echo @in varchar(255) as external name "examples.dll" See create procedure in the Reference Manual for more information. Using sp_addextendedproc sp_addextendedproc is compatible with the syntax used by Microsoft SQL Server. You can use it as an alternative to create procedure. The syntax is: sp_addextendedproc esp_name, dll_name esp_name is the name of the ESP. It must match the name of the function that supports the ESP. dll_name is the name of the DLL containing the ESP’s supporting function. The sp_addextendedproc must be executed in the master database by a user who has the sa_role. Therefore, sp_addextendedproc always registers the ESP in the master database, unlike create procedure, which registers the ESP in the current database. Unlike create procedure, sp_addextendedproc does not allow for parameter checking in Adaptive Server or for default values for parameters. The following statements register in the master database an ESP supported by the xp_echo routine described in the example in “ESP function example” on page 541, assuming that the function is compiled in a DLL named examples.dll: use master sp_addextendedproc "xp_echo", "examples.dll" See the Reference Manual for a complete description of the sp_addextendedproc command.Removing ESPs 552 Adaptive Server Enterprise Removing ESPs You can remove an ESP from the database using either drop procedure or sp_dropextendedproc. The syntax for drop procedure is the same as for stored procedures: drop procedure [owner.]procedure_name The following command drops xp_echo: drop procedure xp_echo The syntax for sp_dropextendedproc is: sp_dropextendedproc esp_name For example: sp_dropextendedproc xp_echo Both methods drop the ESP from the database by removing references to it in the sysobjects and syscomments system tables. They have no effect on the underlying DLL. Renaming ESPs Because an ESP name is bound to the name of its function, you cannot rename an ESP using sp_rename, as you can with a stored procedure. To change the name of an ESP: 1 Remove the ESP with drop procedure or sp_dropextendedproc. 2 Rename and recompile the supporting function. 3 Re-create the ESP with the new name using create procedure or sp_addextendedproc. Executing ESPs Execute an ESP using the same execute command that you use to execute a regular stored procedure. See “Creating and executing stored procedures” on page 495 for syntax and other information about executing stored procedures.CHAPTER 16 Using Extended Stored Procedures Transact-SQL User’s Guide 553 You can also execute an ESP remotely. See “Executing procedures remotely” on page 508 for information about executing remote stored procedures. Because the execution of any ESP involves a remote procedure call between Adaptive Server and XP Server, you cannot combine parameters by name and parameters by value in the same execute command. All the parameters must be passed by name, or all must be passed by value. This is the only way in which the execution of extended stored procedures differs from that of regular stored procedures. ESPs can return: • A status value indicating success or failure, and the reason for failure • Values of output parameters • Result sets An ESP function reports the return status value with the srv_sendstatus Open Server routines. The return status values from srv_sendstatus are application-specific. However, a status of zero indicates that the request completed normally. When there is no parameter declaration list for an extended stored procedure, Adaptive Server ignores all supplied parameters but issues no error message. If you supply more parameters when you execute the ESP than you declare in the declaration list, Adaptive Server calls them anyway. To avoid confusion about what parameters are called, check that the parameters on the declaration list match the parameters supplied at run time. You should also check the number of parameters in the specified ESP at the Open Server function build. An ESP function returns the values of output parameters and result sets using the srv_descfmt, srv_bind, and srv_xferdata Open Server routine. See the “ESP function example” on page 541 and the Open Server ServerLibrary/C Reference Manual for more information about passing values from an ESP function. From the Adaptive Server side, returned values from an ESP are handled as they are for a regular stored procedure.System ESPs 554 Adaptive Server Enterprise System ESPs In addition to xp_cmdshell, there are several system ESPs that support Windows NT features, such as the integration of Adaptive Server with the Windows NT Event Log or Mail System. The names of all system ESPs begin with “xp_”. They are created in the sybsystemprocs database during Adaptive Server installation. Since system ESPs are located in the sybsystemprocs database, their permissions are set there. However, you can run system ESPs from any database. The system ESPs are: • xp_cmdshell • xp_deletemail • xp_enumgroups • xp_findnextmsg • xp_logevent • xp_readmail • xp_sendmail • xp_startmail • xp_stopmail See the Reference Manual for documentation of the system ESPs. In addition, Configuring Adaptive Server for Windows NT discusses some NT-specific features in more detail, such as MAPI and NT Event Log integration, which you implement using the NT-specific system ESPs. Getting information about ESPs Use sp_helpextendedproc to get information about ESPs registered in the current database. With no parameters, sp_helpextendedproc displays all the ESPs in the database, with the names of the DLLs containing their associated functions. With an ESP name as a parameter, it provides this information only for the specified ESP. sp_helpextendedproc getmsgs CHAPTER 16 Using Extended Stored Procedures Transact-SQL User’s Guide 555 ESP Name DLL -------- --------- getmsgs msgs.dll Since the system ESPs are in the sybsystemprocs database, you must be using the sybsystemprocs database to display their names and DLLs: use sybsystemprocs sp_helpextendedproc ESP Name DLL -------- --------- xp_freedll sybyesp xp_cmdshell sybyesp If the source text of an ESP was encrypted using sp_hidetext, Adaptive Server displays a message advising you that the text is hidden. For information about hiding source text, see sp_hidetext in the Reference Manual. ESP exceptions and messages Adaptive Server handles all messages and exceptions from XP Server. It logs standard ESP messages in the log file in addition to sending them to the client. User-defined messages from user-defined ESPs are not logged, but they are sent to the client. ESP-related messages may be generated by XP Server, by a system procedure that creates or manipulates ESPs, or by a system ESP. See the Troubleshooting and Error Messages Guide for the list of ESP-related messages. A function for a user-defined ESP can generate a message using the srv_sendinfo Open Server routine. See the sample xp_message function in the “ESP function example” on page 541. Starting XP Server manually 556 Adaptive Server Enterprise Starting XP Server manually Normally, there is no reason for a user to start XP Server manually, since Adaptive Server starts it when it receives the first ESP request of the session. However, if you are creating and debugging your own ESPs, you may find it necessary to start XP Server manually from the command line using the xpserver utility. See the Utility Guide for your platform for the syntax of xpserver.Transact-SQL User’s Guide 557 C H A P T E R 1 7 Triggers: Enforcing Referential Integrity This chapter discusses triggers, including: How triggers work A trigger is a stored procedure that goes into effect when you insert, delete, or update data in a table. You can use triggers to perform a number of automatic actions, such as cascading changes through related tables, enforcing column restrictions, comparing the results of data modifications, and maintaining the referential integrity of data across a database. Triggers are automatic. They work no matter what caused the data modification—a clerk’s data entry or an application action. A trigger is specific to one or more of the data modification operations, update, insert, and delete and is executed once for each SQL statement. For example, to prevent users from removing any publishing companies from the publishers table, you could use this trigger: create trigger del_pub Topic Page How triggers work 557 Creating triggers 559 Using triggers to maintain referential integrity 561 Multirow considerations 573 Rolling back triggers 577 Nesting triggers 579 Rules associated with triggers 581 Disabling triggers 585 Dropping triggers 586 Getting information about triggers 587How triggers work 558 Adaptive Server Enterprise on publishers for delete as begin rollback transaction print "You cannot delete any publishers!" end The next time someone tries to remove a row from the publishers table, the del_pub trigger cancels the deletion, rolls back the transaction, and prints a message to that effect. A trigger “fires” only after the data modification statement has completed and Adaptive Server has checked for any datatype, rule, or integrity constraint violation. The trigger and the statement that fires it are treated as a single transaction that can be rolled back from within the trigger. If Adaptive Server detects a severe error, the entire transaction is rolled back. Triggers are most useful in these situations: • Triggers can cascade changes through related tables in the database. For example, a delete trigger on the title_id column of the titles table can delete matching rows in other tables, using the title_id column as a unique key to locating rows in titleauthor and roysched. • Triggers can disallow, or roll back, changes that would violate referential integrity, canceling the attempted data modification transaction. Such a trigger might go into effect when you try to insert a foreign key that does not match its primary key. For example, you could create an insert trigger on titleauthor that rolled back an insert if the new titleauthor.title_id value did not have a matching value in titles.title_id. • Triggers can enforce restrictions that are much more complex than those that are defined with rules. Unlike rules, triggers can reference columns or database objects. For example, a trigger can roll back updates that attempt to increase a book’s price by more than 1 percent of the advance. • Triggers can perform simple “what if” analyses. For example, a trigger can compare the state of a table before and after a data modification and take action based on that comparison. CHAPTER 17 Triggers: Enforcing Referential Integrity Transact-SQL User’s Guide 559 Using triggers vs. integrity constraints As an alternative to using triggers, you can use the referential integrity constraint of the create table statement to enforce referential integrity across tables in the database. However, referential integrity constraints cannot: • Cascade changes through related tables in the database • Enforce complex restrictions by referencing other columns or database objects • Perform “what if” analyses Also, referential integrity constraints do not roll back the current transaction as a result of enforcing data integrity. With triggers, you can either roll back or continue the transaction, depending on how you handle referential integrity. For information about transactions, see Chapter 19, “Transactions: Maintaining Data Consistency and Recovery.” If your application requires one of the above tasks, use a trigger. Otherwise, use a referential integrity constraint to enforce data integrity. Adaptive Server checks referential integrity constraints before it checks triggers so that a data modification statement that violates the constraint does not also fire the trigger. For more information about referential integrity constraints, see Chapter 8, “Creating Databases and Tables.” Creating triggers A trigger is a database object. When you create a trigger, you specify the table and the data modification commands that should “fire” or activate the trigger. Then, you specify the action(s) the trigger is to take. For example, this trigger prints a message every time anyone tries to insert, delete, or update data in the titles table: create trigger t1 on titles for insert, update, delete as Creating triggers 560 Adaptive Server Enterprise print "Now modify the titleauthor table the same way." Note Except for the trigger named deltitle, the triggers discussed in this chapter are not included in the pubs2 database shipped with Adaptive Server. To work with the examples shown in this chapter, create each trigger example by typing in the create trigger statement. Each new trigger for the same operation—insert, update or delete—on a table or column overwrites the previous one without warning, and old triggers are dropped automatically. create trigger syntax Here is the complete create trigger syntax: create trigger [owner.]trigger_name on [owner.]table_name {for {insert , update , delete} as SQL_statements Or, using the if update clause: create trigger [owner.]trigger_name on [owner.]table_name for {insert , update} as [if update (column_name ) [{and | or} update (column_name )]...] SQL_statements [if update (column_name ) [{and | or} update (column_name )]... SQL_statements ]... The create clause creates and names the trigger. A trigger’s name must conform to the rules for identifiers. The on clause gives the name of the table that activates the trigger. This table is sometimes called the trigger table. A trigger is created in the current database, although it can reference objects in other databases. The owner name that qualifies the trigger name must be the same as the one in the table. Only a table owner can create a trigger on a table. If the table owner is given with the table name in the create trigger clause or the on clause, it must also be specified in the other clause. The for clause specifies which data modification commands on the trigger table activate the trigger. In the earlier example, an insert, update, or delete to titles makes the message print. CHAPTER 17 Triggers: Enforcing Referential Integrity Transact-SQL User’s Guide 561 The SQL statements specify trigger conditions and trigger actions. Trigger conditions specify additional criteria that determine whether insert, delete, or update causes the trigger actions to be carried out. You can group multiple trigger actions in an if clause with begin and end. An if update clause tests for an insert or update to a specified column. For updates, the if update clause evaluates to true when the column name is included in the set clause of an update statement, even if the update does not change the value of the column. Do not use the if update clause with delete. You can specify more than one column, and you can use more than one if update clause in a create trigger statement. Since you specify the table name in the on clause, do not use the table name in front of the column name with if update. SQL statements that are not allowed in triggers Since triggers execute as part of a transaction, the following statements are not allowed in a trigger: • All create commands, including create database, create table, create index, create procedure, create default, create rule, create trigger, and create view • All drop commands • alter table and alter database • truncate table • grant and revoke • update statistics • reconfigure • load database and load transaction • disk init, disk mirror, disk refit, disk reinit, disk remirror, disk unmirror • select into Using triggers to maintain referential integrity Triggers are used to maintain referential integrity, which assures that vital data in your database—such as the unique identifier for a given piece of data— remains accurate and can be used as the database changes. Referential integrity is coordinated through the use of primary and foreign keys. Using triggers to maintain referential integrity 562 Adaptive Server Enterprise The primary key is a column or combination of columns whose values uniquely identify a row. The value cannot be null and must have a unique index. A table with a primary key is eligible for joins with foreign keys in other tables. Think of the primary key table as the master table in a master-detail relationship. There can be many such master-detail groups in a database. You can use sp_primarykey to mark a primary key. This marks the key for use with sp_helpjoins and adds it to the syskeys table. For example, the title_id column is the primary key of titles. It uniquely identifies the books in titles and joins with title_id in titleauthor, salesdetail, and roysched. The titles table is the master table in relation to titleauthor, salesdetail, and roysched. The “Diagram of the pubs2 database” on page 705 shows how the pubs2 tables are related. The “Diagram of the pubs3 database” on page 739 provides the same information for the pubs3 database. The foreign key is a column or combination of columns whose values match the primary key. A foreign key does not have to be unique. It is often in a manyto-one relationship to a primary key. Foreign key values should be copies of the primary key values. That means no value in the foreign key should exist unless the same value exists in the primary key. A foreign key may be null; if any part of a composite foreign key is null, the entire foreign key must be null. Tables with foreign keys are often called detail tables or dependent tables to the master table. You can use sp_foreignkey to mark foreign keys in your database. This flags them for use with sp_helpjoins and other procedures that reference the syskeys table. The title_id columns in titleauthor, salesdetail, and roysched are foreign keys; the tables are detail tables. In most cases, you can enforce referential integrity between tables using the referential constraints described under “Specifying referential integrity constraints” on page 268, because the maximum number of references allowed for a single table is 200. If a table exceeds that limit, or has special referential integrity needs, use referential integrity triggers. Referential integrity triggers keep the values of foreign keys in line with those in primary keys. When a data modification affects a key column, triggers compare the new column values to related keys by using temporary work tables called trigger test tables. When you write your triggers, you base your comparisons on the data that is temporarily stored in the trigger test tables. CHAPTER 17 Triggers: Enforcing Referential Integrity Transact-SQL User’s Guide 563 Testing data modifications against the trigger test tables Adaptive Server uses two special tables in trigger statements: the deleted table and the inserted table. These are temporary tables used in trigger tests. When you write triggers, you can use these tables to test the effects of a data modification and to set conditions for trigger actions. You cannot directly alter the data in the trigger test tables, but you can use the tables in select statements to detect the effects of an insert, update, or delete. • The deleted table stores copies of the affected rows during delete and update statements. During the execution of a delete or update statement, rows are removed from the trigger table and transferred to the deleted table. The deleted and trigger tables ordinarily have no rows in common. • The inserted table stores copies of the affected rows during insert and update statements. During an insert or an update, new rows are added to the inserted and trigger tables at the same time. The rows in inserted are copies of the new rows in the trigger table. The following trigger fragment uses the inserted table to test for changes to the titles table title_id column: if (select count(*) from titles, inserted where titles.title_id = inserted.title_id) != @@rowcount An update is, effectively, a delete followed by an insert; the old rows are copied to the deleted table first; then the new rows are copied to the trigger table and to the inserted table. The following illustration shows the condition of the trigger test tables during an insert, a delete, and an update: When setting trigger conditions, use the trigger test tables that are appropriate for the data modification. It is not an error to reference deleted while testing an insert or inserted while testing a delete; however, those trigger test tables will not contain any rows. Note A given trigger fires only once per query. If trigger actions depend on the number of rows affected by a data modification, use tests, such as an examination of @@rowcount for multirow data modifications, and take appropriate actions. Using triggers to maintain referential integrity 564 Adaptive Server Enterprise The following trigger examples accommodate multirow data modifications where necessary. The @@rowcount variable, which stores the “number of rows affected” by the most recent data modification operation, tests for a multirow insert, delete, or update. If any other select statement precedes the test on @@rowcount within the trigger, use local variables to store the value for later examination. All Transact-SQL statements that do not return values reset @@rowcount to 0. Insert trigger example When you insert a new foreign key row, make sure the foreign key matches a primary key. The trigger should check for joins between the inserted rows (using the inserted table) and the rows in the primary key table, and then roll back any inserts of foreign keys that do not match a key in the primary key table. The following trigger compares the title_id values from the inserted table with those from the titles table. It assumes that you are making an entry for the foreign key and that you are not inserting a null value. If the join fails, the transaction is rolled back. create trigger forinsertrig1 on salesdetail for insert as if (select count(*) from titles, inserted where titles.title_id = inserted.title_id) != @@rowcount /* Cancel the insert and print a message.*/ begin rollback transaction print "No, the title_id does not exist in titles." end /* Otherwise, allow it. */ else print "Added! All title_id’s exist in titles."CHAPTER 17 Triggers: Enforcing Referential Integrity Transact-SQL User’s Guide 565 @@rowcount refers to the number of rows added to the salesdetail table. This is also the number of rows added to the inserted table. The trigger joins titles and inserted to determine whether all the title_ids added to salesdetail exist in the titles table. If the number of joined rows, which is determined by the select count(*) query, differs from @@rowcount, then one or more of the inserts is incorrect, and the transaction is canceled. This trigger prints one message if the insert is rolled back and another if it is accepted. To test for the first condition, try this insert statement: insert salesdetail values ("7066", "234517", "TC9999", 70, 45) To test for the second condition, enter: insert salesdetail values ("7896", "234518", "TC3218", 75, 80) Delete trigger examples When you delete a primary key row, delete corresponding foreign key rows in dependent tables. This preserves referential integrity by ensuring that detail rows are removed when their master row is deleted. If you do not delete the corresponding rows in the dependent tables, you may end up with a database with detail rows that cannot be retrieved or identified. To properly delete the dependent foreign key rows, use a trigger that performs a cascading delete. Cascading delete example When a delete statement on titles is executed, one or more rows leave the titles table and are added to deleted. A trigger can check the dependent tables— titleauthor, salesdetail, and roysched—to see if they have any rows with a title_id that matches the title_ids removed from titles and is now stored in the deleted table. If the trigger finds any such rows, it removes them. create trigger delcascadetrig on titles for delete as delete titleauthor from titleauthor, deleted where titleauthor.title_id = deleted.title_id /* Remove titleauthor rows that match deleted ** (titles) rows.*/Using triggers to maintain referential integrity 566 Adaptive Server Enterprise delete salesdetail from salesdetail, deleted where salesdetail.title_id = deleted.title_id /* Remove salesdetail rows that match deleted ** (titles) rows.*/ delete roysched from roysched, deleted where roysched.title_id = deleted.title_id /* Remove roysched rows that match deleted ** (titles) rows.*/ Restricted delete examples In practice, you may want to keep some of the detail rows, either for historical purposes (to check how many sales were made on discontinued titles while they were active) or because transactions on the detail rows are not yet complete. A well-written trigger should take these factors into consideration. Preventing primary key deletions The deltitle trigger supplied with pubs2 prevents the deletion of a primary key if there are any detail rows for that key in the salesdetail table. This trigger preserves the ability to retrieve rows from salesdetail: create trigger deltitle on titles for delete as if (select count(*) from deleted, salesdetail where salesdetail.title_id = deleted.title_id) > 0 begin rollback transaction print "You cannot delete a title with sales." end In this trigger, the row or rows deleted from titles are tested by being joined with the salesdetail table. If a join is found, the transaction is canceled. CHAPTER 17 Triggers: Enforcing Referential Integrity Transact-SQL User’s Guide 567 Similarly, the following restricted delete prevents deletes if the primary table, titles, has dependent children in titleauthor. Instead of counting the rows from deleted and titleauthor, it checks to see if title_id was deleted. This method is more efficient for performance reasons because it checks for the existence of a particular row rather than going through the entire table and counting all the rows. Recording errors that occur The next example uses raiserror for error message 35003. raiserror sets a system flag to record that the error occurred. Before trying this example, add error message 35003 to the sysusermessages system table: sp_addmessage 35003, "restrict_dtrig - delete failed: row exists in titleauthor for this title_id." The trigger is: create trigger restrict_dtrig on titles for delete as if exists (select * from titleauthor, deleted where titleauthor.title_id = deleted.title_id) begin rollback transaction raiserror 35003 return end To test this trigger, try this delete statement: delete titles where title_id = "PS2091" Update trigger examples The following example cascades an update from the primary table titles to the dependent tables titleauthor and roysched. create trigger cascade_utrig on titles for update as if update(title_id) begin update titleauthor set title_id = inserted.title_idUsing triggers to maintain referential integrity 568 Adaptive Server Enterprise from titleauthor, deleted, inserted where deleted.title_id = titleauthor.title_id update roysched set title_id = inserted.title_id from roysched, deleted, inserted where deleted.title_id = roysched.title_id update salesdetail set title_id = inserted.title_id from salesdetail, deleted, inserted where deleted.title_id = salesdetail.title_id end To test this trigger, suppose that the book Secrets of Silicon Valley was reclassified to a psychology book from popular_comp. The following query updates the title_id PC8888 to PS8888 in titleauthor, roysched, and titles. update titles set title_id = "PS8888" where title_id = "PC8888" Restricted update triggers A primary key is the unique identifier for its row and for foreign key rows in other tables. Generally, you should not allow updates to primary keys. An attempt to update a primary key should be taken very seriously. In this case, you need to protect referential integrity by rolling back the update unless specified conditions are met. Sybase suggests that you prohibit any editing changes to a primary key, for example by revoking all permissions on that column. However, if you want to prohibit updates only under certain circumstances, use a trigger. Restricted update trigger using date functions The following trigger prevents updates to titles.title_id on the weekend. The if update clause in stopupdatetrig allows you to focus on a particular column, titles.title_id. Modifications to the data in that column cause the trigger to go into action. Changes to the data in other columns do not. When this trigger detects an update that violates the trigger conditions, it cancels the update and prints a message. If you would like to test this one, substitute the current day of the week for “Saturday” or “Sunday”. create trigger stopupdatetrig on titles for update as CHAPTER 17 Triggers: Enforcing Referential Integrity Transact-SQL User’s Guide 569 /* If an attempt is made to change titles.title_id ** on Saturday or Sunday, cancel the update. */ if update (title_id) and datename(dw, getdate()) in ("Saturday", "Sunday") begin rollback transaction print "We do not allow changes to " print "primary keys on the weekend." end Restricted update triggers with multiple actions You can specify multiple trigger actions on more than one column using if update. The following example modifies stopupdatetrig to include additional trigger actions for updates to titles.price or titles.advance. In addition to preventing updates to the primary key on weekends, it prevents updates to the price or advance of a title, unless the total revenue amount for that title surpasses its advance amount. You can use the same trigger name because the modified trigger replaces the old trigger when you create it again. create trigger stopupdatetrig on titles for update as if update (title_id) and datename(dw, getdate()) in ("Saturday", "Sunday") begin rollback transaction print "We do not allow changes to" print "primary keys on the weekend!" end if update (price) or update (advance) if exists (select * from inserted where (inserted.price * inserted.total_sales) < inserted.advance) begin rollback transaction print "We do not allow changes to price or" print "advance for a title until its total" print "revenue exceeds its latest advance." end The next example, created on titles, prevents update if any of the following conditions is true:Using triggers to maintain referential integrity 570 Adaptive Server Enterprise • The user tries to change a value in the primary key title_id in titles • The dependent key pub_id is not found in publishers • The target column does not exist or is null Before you run this example make sure the following error messages exist in sysusermessages: sp_addmessage 35004, "titles_utrg - Update Failed: update of primary keys %1! is not allowed." sp_addmessage 35005, "titles_utrg - Update Failed: %1! not found in authors." The trigger is as follows: create trigger title_utrg on titles for update as begin declare @num_updated int, @col1_var varchar(20), @col2_var varchar(20) /* Determine how many rows were updated. */ select @num_updated = @@rowcount if @num_updated = 0 return /* Ensure that title_id in titles is not changed. */ if update(title_id) begin rollback transaction select @col1_var = title_id from inserted raiserror 35004 , @col1_var return end /* Make sure dependencies to the publishers table are accounted for. */ if update(pub_id) begin if (select count(*) from inserted, publishers where inserted.pub_id = publishers.pub_id and inserted.pub_id is not null) != @num_updated begin rollback transaction select @col1_var = pub_id from inserted raiserror 35005, @col1_var return end end /* If the column is null, raise error 24004 and rollback the ** trigger. If the column is not null, update the roysched tableCHAPTER 17 Triggers: Enforcing Referential Integrity Transact-SQL User’s Guide 571 ** restricting the update. */ if update(price) begin if exists (select count(*) from inserted where price = null) begin rollback trigger with raiserror 24004 "Update failed : Price cannot be null. " end else begin update roysched set lorange = 0, hirange = price * 1000 from inserted where roysched.title_id = inserted.title_id end end end To test for the first error message, 35004, enter: update titles set title_id = "BU7777" where title_id = "BU2075" To test for the second error message, 35005: update titles set pub_id = "7777" where pub_id = "0877" To test for the third error, which generates message 24004: update titles set price = 10.00 where title_id = "PC8888" This query fails because the price column in titles is null. If it were not null, it would have updated the price for title PC8888 and performed the necessary recalculations for the roysched table. Error 24004 is not in sysusermessages but it is valid in this case. It demonstrates the “rollback trigger with raiserror” section of the code.Using triggers to maintain referential integrity 572 Adaptive Server Enterprise Updating a foreign key A change or an update to a foreign key by itself is probably an error. A foreign key is just a copy of the primary key. Never design the two to be independent. If you want to allow updates of a foreign key, you should protect integrity by creating a trigger that checks updates against the master table and rolls them back if they do not match the primary key. In the following example, the trigger tests for two possible sources of failure: either the title_id is not in the salesdetail table or it is not in the titles table. This example uses nested if...else statements. The first if statement is true when the value in the where clause of the update statement does not match a value in salesdetail, that is, the inserted table will not contain any rows, and the select returns a null value. If this test is passed, the next if statement ascertains whether the new row or rows in the inserted table join with any title_id in the titles table. If any row does not join, the transaction is rolled back, and an error message is printed. If the join succeeds, a different message is printed. create trigger forupdatetrig on salesdetail for update as declare @row int /* Save value of rowcount. */ select @row = @@rowcount if update (title_id) begin if (select distinct inserted.title_id from inserted) is null begin rollback transaction print "No, the old title_id must be in" print "salesdetail." end else if (select count(*) from titles, inserted where titles.title_id = inserted.title_id) != @row begin rollback transaction print "No, the new title_id is not in" print "titles." end else print "salesdetail table updated" CHAPTER 17 Triggers: Enforcing Referential Integrity Transact-SQL User’s Guide 573 end Multirow considerations Multirow considerations are particularly important when the function of a trigger is to recalculate summary values, or provide ongoing tallies. Triggers used to maintain summary values should contain group by clauses or subqueries that perform implicit grouping. This creates summary values when more than one row is being inserted, updated, or deleted. Since a group by clause imposes extra overhead, the following examples are written to test whether @@rowcount = 1, meaning that only one row in the trigger table was affected. If @@rowcount = 1, the trigger actions take effect without a group by clause. Insert trigger example using multiple rows The following insert trigger updates the total_sales column in the titles table every time a new salesdetail row is added. It goes into effect whenever you record a sale by adding a row to the salesdetail table. It updates the total_sales column in the titles table so that total_sales is equal to its previous value plus the value added to salesdetail.qty. This keeps the totals up to date for inserts into salesdetail.qty. create trigger intrig on salesdetail for insert as /* check value of @@rowcount */ if @@rowcount = 1 update titles set total_sales = total_sales + qty from inserted where titles.title_id = inserted.title_id else /* when @@rowcount is greater than 1, use a group by clause */ update titles set total_sales = total_sales + (select sum(qty) from inserted group by inserted.title_id Multirow considerations 574 Adaptive Server Enterprise having titles.title_id = inserted.title_id) Delete trigger example using multiple rows The next example is a delete trigger that updates the total_sales column in the titles table every time one or more salesdetail rows are deleted. create trigger deltrig on salesdetail for delete as /* check value of @@rowcount */ if @@rowcount = 1 update titles set total_sales = total_sales - qty from deleted where titles.title_id = deleted.title_id else /* when rowcount is greater than 1, use a group by clause */ update titles set total_sales = total_sales - (select sum(qty) from deleted group by deleted.title_id having titles.title_id = deleted.title_id) This trigger goes into effect whenever a row is deleted from the salesdetail table. It updates the total_sales column in the titles table so that total_sales is equal to its previous value minus the value subtracted from salesdetail.qty. Update trigger example using multiple rows The following update trigger updates the total_sales column in the titles table every time the qty field in a salesdetail row is updated. Recall that an update is an insert followed by a delete. This trigger references both the inserted and the deleted trigger test tables. create trigger updtrig on salesdetail for update as if update (qty) CHAPTER 17 Triggers: Enforcing Referential Integrity Transact-SQL User’s Guide 575 begin /* check value of @@rowcount */ if @@rowcount = 1 update titles set total_sales = total_sales + inserted.qty - deleted.qty from inserted, deleted where titles.title_id = inserted.title_id and inserted.title_id = deleted.title_id else /* when rowcount is greater than 1, use a group by clause */ begin update titles set total_sales = total_sales + (select sum(qty) from inserted group by inserted.title_id having titles.title_id = inserted.title_id) update titles set total_sales = total_sales - (select sum(qty) from deleted group by deleted.title_id having titles.title_id = deleted.title_id) end end Conditional insert trigger example using multiple rows You do not have to roll back all data modifications simply because some of them are unacceptable. Using a correlated subquery in a trigger can force the trigger to examine the modified rows one by one. See “Using correlated subqueries” on page 148 for more information on correlated subqueries. The trigger can then take different actions on different rows. The following trigger example assumes the existence of a table called junesales. Here is its create statement: create table junesales (stor_id char(4) not null, ord_num varchar(20) not null, title_id tid not null, Multirow considerations 576 Adaptive Server Enterprise qty smallint not null, discount float not null) You should insert four rows in the junesales table, to test the conditional trigger. Two of the junesales rows have title_ids that do not match any of those already in the titles table. insert junesales values ("7066", "BA27619", "PS1372", 75, 40) insert junesales values ("7066", "BA27619", "BU7832", 100, 40) insert junesales values ("7067", "NB-1.242", "PSxxxx", 50, 40) insert junesales values ("7131", "PSyyyy", "PSyyyy", 50, 40) When you insert data from junesales into salesdetail, the statement looks like this: insert salesdetail select * from junesales The trigger conditionalinsert analyzes the insert row by row and deletes the rows that do not have a title_id in titles: create trigger conditionalinsert on salesdetail for insert as if (select count(*) from titles, inserted where titles.title_id = inserted.title_id) != @@rowcount begin delete salesdetail from salesdetail, inserted where salesdetail.title_id = inserted.title_id and inserted.title_id not in (select title_id from titles) print "Only records with matching title_ids added." end The trigger deletes the unwanted rows. This ability to delete rows that have just been inserted relies on the order in which processing occurs when triggers are fired. First, the rows are inserted into the table and the inserted table; then, the trigger fires. CHAPTER 17 Triggers: Enforcing Referential Integrity Transact-SQL User’s Guide 577 Rolling back triggers You can roll back triggers using either the rollback trigger statement or the rollback transaction statement (if the trigger is fired as part of a transaction). However, rollback trigger rolls back only the effect of the trigger and the statement that caused the trigger to fire; rollback transaction rolls back the entire transaction. For example: begin tran insert into publishers (pub_id) values ("9999") insert into publishers (pub_id) values ("9998") commit tran If the second insert statement causes a trigger on publishers to issue a rollback trigger, only that insert is affected; the first insert is not rolled back. If that trigger issues a rollback transaction instead, both insert statements are rolled back as part of the transaction. The syntax for rollback trigger is: rollback trigger [with raiserror_statement] The syntax for rollback transaction is described in Chapter 19, “Transactions: Maintaining Data Consistency and Recovery.” raiserror_statement is a statement that prints a user-defined error message and sets a system flag to record that an error condition has occurred. This provides the ability to raise an error to the client when the rollback trigger is executed, so that the transaction state in the error reflects the rollback. For example: rollback trigger with raiserror 25002 "title_id does not exist in titles table." For more information about raiserror, see Chapter 14, “Using Batches and Control-of-Flow Language.” The following example of an insert trigger performs a similar task to the trigger forinsertrig1 described in “Insert trigger example” on page 564. However, this trigger uses a rollback trigger instead of a rollback transaction to raise an error when it rolls back the insertion but not the transaction. create trigger forinsertrig2 on salesdetail for insert as if (select count(*) from titles, inserted where titles.title_id = inserted.title_id) != @@rowcount Rolling back triggers 578 Adaptive Server Enterprise rollback trigger with raiserror 25003 "Trigger rollback: salesdetail row not added because a title_id does not exist in titles." When the rollback trigger is executed, Adaptive Server aborts the currently executing command and halts execution of the rest of the trigger. If the trigger that issues the rollback trigger is nested within other triggers, Adaptive Server rolls back all the work done in these triggers up to and including the update that caused the first trigger to fire. When triggers that include rollback transaction statements are executed from a batch, they abort the entire batch. In the following example, if the insert statement fires a trigger that includes a rollback transaction (such as forinsertrig1), the delete statement will not be executed, since the batch will be aborted: insert salesdetail values ("7777", "JR123", "PS9999", 75, 40) delete salesdetail where stor_id = "7067" If triggers that include rollback transaction statements are fired from within a user-defined transaction, the rollback transaction rolls back the entire batch. In the following example, if the insert statement fires a trigger that includes a rollback transaction, the update statement will also be rolled back: begin tran update stores set payterms = "Net 30" where stor_id = "8042" insert salesdetail values ("7777", "JR123", "PS9999", 75, 40) commit tran See Chapter 19, “Transactions: Maintaining Data Consistency and Recovery,” for information on user-defined transactions. Adaptive Server ignores a rollback trigger executed outside of a trigger and does not issue a raiserror associated with the statement. However, a rollback trigger executed outside a trigger but inside a transaction generates an error that causes Adaptive Server to roll back the transaction and abort the current statement batch.CHAPTER 17 Triggers: Enforcing Referential Integrity Transact-SQL User’s Guide 579 Nesting triggers Triggers can nest to a depth of 16 levels. The current nesting level is stored in the @@nestlevel global variable. Nesting is enabled at installation. A System Administrator can turn trigger nesting on and off with the allow nested triggers configuration parameter. If nested triggers are enabled, a trigger that changes a table on which there is another trigger fires the second trigger, which can in turn fire a third trigger, and so forth. If any trigger in the chain sets off an infinite loop, the nesting level is exceeded and the trigger aborts. You can use nested triggers to perform useful housekeeping functions such as storing a backup copy of rows affected by a previous trigger. For example, you can create a trigger on titleauthor that saves a backup copy of titleauthor rows that was deleted by the delcascadetrig trigger. With the delcascadetrig trigger in effect, deleting the title_id “PS2091” from titles also deletes the corresponding row(s) from titleauthor. To save the data, you can create a delete trigger on titleauthor that saves the deleted data in another table, del_save: create trigger savedel on titleauthor for delete as insert del_save select * from deleted Sybase suggests that you use nested triggers in an order-dependent sequence. Use separate triggers to cascade data modifications, as in the earlier example of delcascadetrig, described under “Cascading delete example” on page 565. Note When you put triggers into a transaction, a failure at any level of a set of nested triggers cancels the transaction and rolls back all data modifications. Use print or raiserror statements in your triggers to determine where failures occur. A rollback transaction in a trigger at any nesting level rolls back the effects of each trigger and cancels the entire transaction. A rollback trigger affects only the nested triggers and the data modification statement that caused the initial trigger to fire. Nesting triggers 580 Adaptive Server Enterprise Trigger self-recursion By default, a trigger does not call itself recursively. That is, an update trigger does not call itself in response to a second update to the same table within the trigger. If an update trigger on one column of a table results in an update to another column, the update trigger fires only once. However, you can turn on the self_recursion option of the set command to allow triggers to call themselves recursively. The allow nested triggers configuration variable must also be enabled for self-recursion to occur. The self_recursion setting remains in effect only for the duration of a current client session. If the option is set as part of a trigger, its effect is limited by the scope of the trigger that sets it. If the trigger that sets self_recursion on returns or causes another trigger to fire, this option reverts to off. Once a trigger turns on the self_recursion option, it can repeatedly loop, if its own actions cause it to fire again, but it cannot exceed the limit of 16 nesting levels. For example, assume that the following new_budget table exists in pubs2: select * from new_budget unit parent_unit budget --------------- --------------- ------- one_department one_division 10 one_division company_wide 100 company_wide NULL 1000 (3 rows affected) You can create a trigger that recursively updates new_budget whenever its budget column is changed, as follows: create trigger budget_change on new_budget for update as if exists (select * from inserted where parent_unit is not null) begin set self_recursion on update new_budget set new_budget.budget = new_budget.budget + inserted.budget - deleted.budget from inserted, deleted, new_budget where new_budget.unit = inserted.parent_unit and new_budget.unit = deleted.parent_unit endCHAPTER 17 Triggers: Enforcing Referential Integrity Transact-SQL User’s Guide 581 If you update new_budget.budget by increasing the budget of unit one_department by 3, Adaptive Server behaves as follows (assuming that nested triggers are enabled): 1 Increasing one_department from 10 to 13 fires the budget_change trigger. 2 The trigger updates the budget of the parent of one_department (in this case one_division) from 100 to 103, which fires the trigger again. 3 The trigger updates the parent of one_division (in this case company_wide) from 1000 to 1003, which causes the trigger to fire for the third time. 4 The trigger attempts to update the parent of company_wide, but since none exists (the value is “NULL”), the last update never occurs and the trigger is not fired, ending the self-recursion. You can query new_budget to see the final results, as follows: select * from new_budget unit parent_unit budget --------------- --------------- ------- one_department one_division 13 one_division company_wide 103 company_wide NULL 1003 (3 rows affected) A trigger can also be recursively executed in other ways. A trigger calls a stored procedure that performs actions that cause the trigger to fire again (it is reactivated only if nested triggers are enabled). Unless conditions within the trigger limit the number of recursions, the nesting level can overflow. For example, if an update trigger calls a stored procedure that performs an update, the trigger and stored procedure execute only once if nested triggers is set to off. If nested triggers is set to on, and the number of updates exceeds 16 by some condition in the trigger or procedure, the loop continues until the trigger or procedure exceeds the 16-level maximum nesting value. Rules associated with triggers Apart from anticipating the effects of a multirow data modification, trigger rollbacks, and trigger nesting, consider the following factors when you are writing triggers.Rules associated with triggers 582 Adaptive Server Enterprise Triggers and permissions A trigger is defined on a particular table. Only the owner of the table has create trigger and drop trigger permissions for the table. These permissions cannot be transferred to others. Adaptive Server will accept a trigger definition that attempts actions for which you do not have permission. The existence of such a trigger aborts any attempt to modify the trigger table because incorrect permissions will cause the trigger to fire and fail. The transaction will be canceled. You must rectify the permissions or drop the trigger. For example, Jose owns salesdetail and creates a trigger on it. The trigger is supposed to update titles.total_sales when salesdetail.qty is updated. However, Mary is the owner of titles, and has not granted Jose permission on titles. When Jose tries to update salesdetail, Adaptive Server detects the trigger and Jose’s lack of permissions on titles, and rolls back the update transaction. Jose must either get update permission on titles.total_sales from Mary or drop the trigger on salesdetail. Trigger restrictions Adaptive Server imposes the following limitations on triggers: • A table can have a maximum of three triggers: one update trigger, one insert trigger, and one delete trigger. • Each trigger can apply to only one table. However, a single trigger can apply to all three user actions: update, insert, and delete. • You cannot create a trigger on a view or on a temporary table, though triggers can reference views or temporary tables. • The writetext statement will not activate insert or update triggers. • Although a truncate table statement is, in effect, like a delete without a where clause, because it removes all rows, it cannot fire a trigger, because individual row deletions are not logged. • You cannot create a trigger or build an index or a view on a temporary object (@object) • You cannot create triggers on system tables. If you try to create a trigger on a system table, Adaptive Server returns an error message and cancels the trigger.CHAPTER 17 Triggers: Enforcing Referential Integrity Transact-SQL User’s Guide 583 • You cannot use triggers that select from a text column or an image column of the inserted or deleted table. • If Component Integration Services is enabled, triggers have limited usefulness on proxy tables because you cannot examine the rows being inserted, updated, or deleted (via the inserted and deleted tables). You can create a trigger on a proxy table, and it can be invoked. However, deleted or inserted data is not written to the transaction log for proxy tables because the insert is passed to the remote server. Hence, the inserted and deleted tables, which are actually views to the transaction log, contain no data for proxy tables. Implicit and explicit null values The if update(column_name) clause is true for an insert statement whenever the column is assigned a value in the select list or in the values clause. An explicit null or a default assigns a value to a column, and thus activates the trigger. An implicit null does not. For example, suppose you create the following table: create table junk (a int null, b int not null) and then write the following trigger: create trigger junktrig on junk for insert as if update(a) and update(b) print "FIRING" /*"if update" is true for both columns. The trigger is activated.*/ insert junk (a, b) values (1, 2) /*"if update" is true for both columns. The trigger is activated.*/ insert junk values (1, 2) /*Explicit NULL: "if update" is true for both columns. The trigger is activated.*/Rules associated with triggers 584 Adaptive Server Enterprise insert junk values (NULL, 2) /* If default exists on column a, "if update" is true for either column. The trigger is activated.*/ insert junk (b) values (2) /* If no default exists on column a, "if update" is not true for column a. The trigger is not activated.*/ insert junk (b) values (2) The same results would be produced using only the clause: if update(a) To create a trigger that disallows the insertion of implicit nulls, you can use: if update(a) or update(b) SQL statements in the trigger can then test to see if a or b is null. Triggers and performance In terms of performance, trigger overhead is usually very low. The time involved in running a trigger is spent mostly in referencing other tables, which may be either in memory or on the database device. The deleted and inserted trigger test tables are always in active memory. The location of other tables referenced by the trigger determines the amount of time the operation takes. For more information on how triggers affect performance, see the Performance and Tuning Guide. set commands in triggers You can use the set command inside a trigger. The set option you invoke remains in effect during execution of the trigger. Then, the trigger reverts to its former setting. CHAPTER 17 Triggers: Enforcing Referential Integrity Transact-SQL User’s Guide 585 Renaming and triggers If you change the name of an object referenced by a trigger, you must drop the trigger and re-create it so that its source text reflects the new name of the object being referenced. Use sp_depends to get a report of the objects referenced by a trigger. The safest course of action is to not rename any tables or views that are referenced by a trigger. Trigger tips Consider the following tips when creating triggers: • Suppose you have an insert or update trigger that calls a stored procedure, which in turn updates the base table. If the nested triggers configuration parameter is set to true, the trigger will enter an infinite loop. Before executing an insert or update trigger, set sp_configure “nested triggers” to false. • When you execute drop table, any triggers dependent on that table are also dropped. If you want to preserve any such triggers, change their names with sp_rename before dropping the table. • Use sp_depends to see a report on the tables and views referred to in a trigger. • Use sp_rename to rename a trigger. • A trigger fires only once per query (a single data modification such as an insert or update). If the query is repeated in a loop, the trigger fires as many times as the query is repeated. Disabling triggers The insert, update, and delete commands normally fire any trigger they encounter, which increases the time needed to perform the operation.To disable triggers during bulk insert, update, or delete operations, you can use the disable trigger option of the alter table command. You can use the disable trigger option either to disable all the triggers associated with the table, or to specify a particular trigger to disable. However, any triggers you disable will not be fired after the copy is complete.Dropping triggers 586 Adaptive Server Enterprise bcp, to maintain maximum speed for loading data, does not fire rules and triggers. To find any rows that violate rules and triggers, copy the data into the table and run queries or stored procedures that test the rule or trigger conditions. alter table... disable trigger uses this syntax: alter table [database_name.[owner_name].]table_name {enable | disable } trigger [trigger_name] Where table_name is the name of the table for which you are disabling triggers, and trigger_name is the name of the trigger you are disabling. For example, to disable the del_pub trigger in the pubs2 database: alter table pubs2 disable del_pubs If you do not specify a trigger, alter table disables all the triggers defined in the table. Use alter table... enable trigger to reenable the triggers after the load database is complete. To reenable the del_pub trigger, issue: alter table pubs2 enable del_pubs Note You can use the disable trigger feature only if you are the table owner or database administrator. If a trigger includes any insert, update, or delete statements, these statements will not run while the trigger is disabled, which may affect the referential integrity of a table. Dropping triggers You can remove a trigger by dropping it or by dropping the trigger table with which it is associated. The drop trigger syntax is: drop trigger [owner.]trigger_name [, [owner.]trigger_name]...CHAPTER 17 Triggers: Enforcing Referential Integrity Transact-SQL User’s Guide 587 When you drop a table, Adaptive Server drops any triggers associated with it. drop trigger permission defaults to the trigger table owner and is not transferable. Getting information about triggers As database objects, triggers are listed in sysobjects by name. The type column of sysobjects identifies triggers with the abbreviation “TR”. This query finds the triggers that exist in a database: select * from sysobjects where type = "TR" The source text for each trigger is stored in syscomments. Execution plans for triggers are stored in sysprocedures. The system procedures described in the following sections provide information from the system tables about triggers. sp_help You can get a report on a trigger using sp_help. For example, you can get information on deltitle as follows: sp_help deltitle Name Owner Type ----------- ------- ----------- deltitle dbo trigger Data_located_on_segment When_created ----------------------- ----------------- not applicable Jul 10 1997 3:56PM (return status = 0) You can also use sp_help to report the status of a disabled or enabled trigger: 1> sp_help trig_insert 2> go Name Owner Type ------------------------------------ trig_insert dboGetting information about triggers 588 Adaptive Server Enterprise trigger (1 row affected) data_located_on_segment When_created ------------------------------------ not applicable Aug 30 1998 11:40PM Trigger enabled (return status = 0) sp_helptext To display the source text of a trigger, execute sp_helptext, as follows: sp_helptext deltitle # Lines of Text --------------- 1 text --------------------------------------------- create trigger deltitle on titles for delete as if (select count(*) from deleted, salesdetail where salesdetail.title_id = deleted.title_id) >0 begin rollback transaction print "You can’t delete a title with sales." end If the source text of a trigger was encrypted using sp_hidetext, Adaptive Server displays a message advising you that the text is hidden. For information about hiding source text, see sp_hidetext in the Reference Manual. If the System Security Officer has reset the allow select on syscomments.text column parameter with sp_configure (as required to run Adaptive Server in the evaluated configuration), you must be the creator of the trigger or a System Administrator to view the source text of a trigger through sp_helptext. (See evaluated configuration in the Adaptive Server Glossary for more information.) CHAPTER 17 Triggers: Enforcing Referential Integrity Transact-SQL User’s Guide 589 sp_depends sp_depends lists the triggers that reference an object or all the tables or views that the trigger affects. This example shows how to use sp_depends to get a list of all the objects referenced by the trigger deltitle: sp_depends deltitle Things the object references in the current database. object type updated selected ---------------- ---------- ------- -------- dbo.salesdetail user table no no dbo.titles user table no no (return status = 0) This statement lists all the objects that reference the salesdetail table: sp_depends salesdetail Things inside the current database that reference the object. object type --------------------------- ---------------- dbo.deltitle trigger dbo.history_proc stored procedure dbo.insert_salesdetail_proc stored procedure dbo.totalsales_trig trigger (return status = 0)Getting information about triggers 590 Adaptive Server EnterpriseTransact-SQL User’s Guide 591 C H A P T E R 1 8 Cursors: Accessing Data Row by Row A cursor accesses the results of a SQL select statement one or more rows at a time. Cursors allow you to modify or delete rows on an individual basis. This chapter discusses: For information on how cursors affect performance, see the Performance and Tuning Guide. How cursors work A cursor is a symbolic name associated with a select statement. It consists of the following parts: • Cursor result set – the set (table) of rows resulting from the execution of a query that is associated with the cursor. • Cursor position – a pointer to one row within the cursor result set. Topic Page How cursors work 591 Declaring cursors 596 Opening cursors 604 Fetching data rows using cursors 604 Updating and deleting rows using cursors 608 Closing and deallocating cursors 610 An example using a cursor 611 Using cursors in stored procedures 613 Cursors and locking 615 Getting information about cursors 617 Using browse mode instead of cursors 618 Join cursor processing and data modifications 620How cursors work 592 Adaptive Server Enterprise The cursor position indicates the current row of the cursor. You can explicitly modify or delete that row using update or delete statements with a clause naming the cursor. You can change the current cursor position through an operation called a fetch. The fetch command moves the current cursor position one or more rows down the cursor result set. Figure 17-1 illustrates how the cursor result set and cursor position work when a fetch command is performed. In this example, the cursor is defined as follows: declare cal_authors_crsr cursor for select au_id, au_lname, au_fname from authors where state = "CA" for update Figure 18-1: How the cursor result set and cursor position work for a fetch You might think of a cursor as a “handle” on the result set of a select statement. It enables you to examine and possibly manipulate one row at a time. However, cursors support only forward (or sequential) movement through the query results. Once you fetch several rows, you cannot backtrack through the cursor result set to access them again. How Adaptive Server processes cursors Figure 17-2 shows the steps in using cursors.CHAPTER 18 Cursors: Accessing Data Row by Row Transact-SQL User’s Guide 593 Figure 18-2: Using cursors When accessing data using cursors, Adaptive Server divides the process into several operations: • Declaring the cursor If you declare the cursor within a stored procedure, Adaptive Server creates the cursor structure and compiles the query defined for that cursor. It stores the compiled query plan but does not execute it. For example, the following cursor declaration, business_crsr, finds the titles and identification numbers of all business books in the titles table. It also allows you to update the price column in the future through the cursor: declare business_crsr cursor for select title, title_id from titles where type = "business" for update of priceHow cursors work 594 Adaptive Server Enterprise Use the for update clause when declaring a cursor, to ensure that Adaptive Server performs the positioned updates correctly. • Opening the cursor When a cursor that has been declared outside of a stored procedure is opened, Adaptive Server generates an optimized query plan and compiles the cursor. It then performs preliminary operations for executing the scan defined in the cursor and returning a result set. For example, when a cursor is opened, Adaptive Server may place a shared intent lock on a table or create a work table. If a cursor has been declared within a stored procedure, it already exists in compiled form. When the cursor is opened, Adaptive Server only needs to perform preliminary operations for executing a scan and returning a result set. • Fetching from the cursor The fetch command executes the compiled cursor to return one or more rows meeting the conditions defined in the cursor. By default, a fetch returns only a single row. The first fetch returns the first row that meets the cursor’s search conditions and stores the current position of the cursor. The second fetch uses the cursor position from the first fetch, returns the next row that meets the search conditions, and stores its current position. Each subsequent fetch uses the cursor position of the previous fetch to locate the next cursor result. The number of rows returned by a fetch can be specified using the set cursor rows command. See “Getting multiple rows with each fetch” on page 606. In the following example, the fetch command displays the title and identification number of the first row in the titles table containing a business book: fetch business_crsr title title_id ----------------------------------- -------- The Busy Executive’s Database Guide BU1032 (1 row affected) Running fetch business_crsr a second time displays the title and identification number of the next business book in titles. • Processing the row by examining, updating, or deleting it through the cursorCHAPTER 18 Cursors: Accessing Data Row by Row Transact-SQL User’s Guide 595 Adaptive Server updates or deletes the data in the cursor result set (and corresponding base tables that derived the data) at the current cursor position after a fetch. This operation is optional. The following update statement raises the price of business books by 5 percent; it affects only the book currently pointed to by the business_crsr cursor: update titles set price = price * .05 + price where current of business_crsr Updating a cursor row involves changing data in the row or deleting the row completely. You cannot use cursors to insert rows. All updates through a cursor affect the corresponding base tables included in the cursor result set. • Closing the cursor Adaptive Server closes the cursor result set, removes any remaining temporary tables, and releases the server resources held for the cursor structure. However, it keeps the query plan for the cursor so that it can be opened again. For example: close business_crsr When you close a cursor and then reopen it, Adaptive Server is ready to re-create the cursor result set. When you perform the fetch, Adaptive Server positions the cursor before the first valid row. This allows you to process a cursor result set as many times as necessary. You can close the cursor at any time; you do not have to go through the entire result set. • Deallocating the cursor Adaptive Server dumps the query plan from memory and eliminates all trace of the cursor structure. For example: deallocate cursor business_crsr You must declare the cursor again before using it. Declaring cursors 596 Adaptive Server Enterprise Declaring cursors You must declare a cursor before you can use it. The declaration specifies the query that defines the cursor result set. You can explicitly define a cursor as updatable or read-only by using the for update or for read only keywords. If you omit either one, Adaptive Server determines whether the cursor is updatable based on the type of query that defines the cursor result set. However, Sybase suggests that you explicitly specify one or the other; for updates, this ensures that Adaptive Server performs the positioned updates correctly. You cannot use the update or delete statements on the result set of a read-only cursor. declare cursor syntax The syntax of the declare cursor statement is: declare cursor_name cursor for select_statement [for {read only | update [of column_name_list]}] The cursor_name is the name of the cursor. It must be a valid Adaptive Server identifier containing no more than 30 characters, and it must start with a letter, a pound sign (#), or an underscore (_). The select_statement is the query that defines the cursor result set. See select in the Reference Manual for information about its options. In general, select_statement may use the full syntax and semantics of a Transact-SQL select statement, including the holdlock keyword. However, it cannot contain a compute, for browse, or into clause. The for read only option specifies that the cursor result set cannot be updated. In contrast, the for update option specifies that the cursor result set is updatable. You can specify of column_name_list after for update with the list of columns from the select_statement defined as updatable. The declare cursor statement must precede any open statement for that cursor. You cannot combine declare cursor with other statements in the same Transact-SQL batch, except when using a cursor in a stored procedure. For example, the following declare cursor statement defines a result set for the authors_crsr cursor that contains all authors that do not reside in California: declare authors_crsr cursorCHAPTER 18 Cursors: Accessing Data Row by Row Transact-SQL User’s Guide 597 for select au_id, au_lname, au_fname from authors where state != "CA" for update The select_statement can contain references to Transact-SQL parameter names or local variables. However, the names can reference only the parameters and local variables defined in a stored procedure that contains the declare cursor statement. If the cursor is used in a trigger, the select_statement can also reference the inserted and deleted temporary tables that are used in triggers. For information on using the select statement, see Chapter 2, “Queries: Selecting Data from a Table.” Types of cursors There are four types of cursors: • Client cursors – are declared through Open Client calls (or Embedded SQL). Open Client keeps track of the rows returned from Adaptive Server and buffers them for the application. Updates and deletes to the result set of client cursors can be done only through the Open Client calls. • Execute cursors – are a subset of client cursors whose result set is defined by a stored procedure. The stored procedure can use parameters. The values of the parameters are sent through Open Client calls. • Server cursors – are declared in SQL. If they are used in stored procedures, the client executing the stored procedure is not aware of them. Results returned to the client for a fetch are the same as the results from a normal select. • Language cursors – are declared in SQL without using Open Client. As with server cursors, the client is not aware of the cursors, and the results are returned to the client in the same format as a normal select. Client cursors, through the use of applications using Open Client calls or Embedded-SQL, are the most frequently used form of cursors. To simplify the discussion of cursors, the examples in this manual are for language and server cursors only. For examples of client or execute cursors, see your Open Client or Embedded-SQL documentation.Declaring cursors 598 Adaptive Server Enterprise Cursor scope A cursor’s existence depends on its scope. The scope refers to the context in which the cursor is used: within a user session, a stored procedure, or a trigger. Within a user session, the cursor exists only until the user ends the session. The cursor does not exist for any additional sessions that other users start. After the user logs off, Adaptive Server deallocates the cursors created in that session. If a declare cursor statement is part of a stored procedure or trigger, the cursor created within it applies to that scope and to the scope that launched the stored procedure or trigger. However, cursors declared inside a trigger on an inserted or a deleted table are not accessible to any nested stored procedures or triggers. Such cursors are accessible within the scope of that trigger. Once the stored procedure or trigger completes, Adaptive Server deallocates the cursors created within it. Figure 17-3 illustrates how cursors operate between scopes. CHAPTER 18 Cursors: Accessing Data Row by Row Transact-SQL User’s Guide 599 Figure 18-3: How cursors operate within scopes A cursor name must be unique within a given scope. Adaptive Server detects name conflicts within a particular scope only during runtime. A stored procedure or trigger can define two cursors with the same name if only one is executed. For example, the following stored procedure works because only one names_crsr cursor is defined in its scope: create procedure proc2 @flag int as if @flag > 0 declare names_crsr cursor for select au_fname from authors else declare names_crsr cursor for select au_lname from authors returnDeclaring cursors 600 Adaptive Server Enterprise Cursor scans and the cursor result set The method Adaptive Server uses to create the cursor result set depends on the type of query used. If the query does not require a worktable, Adaptive Server performs a fetch by cursoring down the base table using the table’s index keys, much like a select statement, except that it returns the number of rows specified by the fetch. After the fetch, Adaptive Server positions the cursor at the next valid index key, until you fetch again or close the cursor. Some queries use worktables to generate the cursor result set. To verify whether a particular cursor uses a worktable, check the output of a set showplan, no exec on statement. Be aware that when a worktable is used, the rows retrieved with a cursor fetch statement may not reflect the values in the actual base table rows. For example, a cursor declared with an order by clause usually requires the creation of a worktable to order the rows for the cursor result set. Adaptive Server does not lock the rows in the base table that correspond to the rows in the worktable, which permits other clients to update these base table rows. Hence, the rows returned to the client from the cursor statement are different from the base table rows. See “Cursors and locking” on page 615 for more information on how locks work with cursors. A cursor result set is generated as the rows are returned through a fetch of that cursor. This means that a cursor select query is processed like a normal select query. This process, known as cursor scans, provides a faster turnaround time and eliminates the need to read rows the application does not require. Adaptive Server requires that cursor scans use a unique index of a table, particularly for isolation level 0 reads. If the table has an IDENTITY column and you need to create a nonunique index on it, use the identity in nonunique index database option to include an IDENTITY column in the table’s index keys so that all indexes created on the table are unique. This database option makes logically nonunique indexes internally unique and allows the indexes to be used to process updatable cursors for isolation level 0 reads. You can still use cursors that reference tables without indexes, if none of those tables are updated by another process that causes the current row position to move. For example: declare storinfo_crsr cursor for select stor_id, stor_name, payterms from storesCHAPTER 18 Cursors: Accessing Data Row by Row Transact-SQL User’s Guide 601 where state = "CA" The table stores, specified with the above cursor, does not have any indexes. Adaptive Server allows the declaration of cursors on tables without unique indexes, as long as you have not specified for update in the declare cursor statement. If an update does not change the position of the row, the cursor position does not change until the next fetch. Making cursors updatable You can update or delete a row returned by a cursor if the cursor is updatable. If the cursor is read-only, you can only read the data; you cannot update or delete it. By default, Adaptive Server attempts to determine whether a cursor is updatable before designating it as read-only. You can explicitly specify whether a cursor is updatable by using the read only or update keywords in the declare statement. Specifying a cursor to be updatable ensures that Adaptive Server performs the positioned updates correctly. Make sure the table being updated has a unique index. If it does not, Adaptive Server rejects the declare cursor statement. The following example defines an updatable result set for the pubs_crsr cursor: declare pubs_crsr cursor for select pub_name, city, state from publishers for update of city, state The above example includes all the rows from the publishers table, but it explicitly defines only the city and state columns for update. Unless you plan to update or delete rows through a cursor, you should declare a cursor as read-only. If you do not explicitly specify read only or update, the cursor is implicitly updatable when the select statement does not contain any of the following constructs: • distinct option • group by clause • Aggregate function • Subquery • union operator • at isolation read uncommitted clauseDeclaring cursors 602 Adaptive Server Enterprise You cannot specify the for update clause if a cursor’s select_statement contains one of the above constructs. Adaptive Server also defines a cursor as read-only if you declare certain types of cursors that include an order by clause as part of their select_statement. See “Types of cursors” on page 597 for information on the types of cursors Adaptive Server supports. Determining which columns can be updated If you do not specify a column_name_list with the for update clause, all the specified columns in the query are updatable. Adaptive Server attempts to use unique indexes for updatable cursors when scanning the base table. For cursors, Adaptive Server considers an index containing an IDENTITY column to be unique, even if it is not so declared. Adaptive Server allows you to update columns in the column_name_list that are not specified in the list of columns of the cursor’s select_statement, but that are part of the tables specified in the select_statement. However, when you specify a column_name_list with for update, you can update only the columns in that list. In the following example, Adaptive Server uses the unique index on the pub_id column of publishers (even though pub_id is not included in the definition of newpubs_crsr): declare newpubs_crsr cursor for select pub_name, city, state from publishers for update If you do not specify the for update clause, Adaptive Server chooses any unique index, although it can also use other indexes or table scans if no unique index exists for the specified table columns. However, when you specify the for update clause, Adaptive Server must use a unique index defined for one or more of the columns to scan the base table. If no unique index exists, Adaptive Server returns an error message.CHAPTER 18 Cursors: Accessing Data Row by Row Transact-SQL User’s Guide 603 In most cases, you should include only columns to be updated in the column_name_list of the for update clause. If the table has only one unique index, you do not need to include its column in the for update column_name_list; Adaptive Server finds it during the cursor scan. If the table has more than one unique index, include its column in the for update column_name_list, so that Adaptive Server can find it quickly for the cursor scan. For example, the table used in the following declare cursor statement has one unique index, on the column c3, so that column should not be included in the for update list: declare mycursor cursor for select c1, c2, 3 from mytable for update of c1, c2 However, if mytable has more than one unique index, for example, on columns c3 and c4, you need to specify one unique index in the for update clause as follows: declare mycursor cursor for select c1, c2, 3 from mytable for update of c1, c2, c3 Allowing Adaptive Server to use the unique index in the cursor scan in this manner helps to prevent an update anomaly called the Halloween problem. The Halloween problem occurs when a client updates a column through a cursor, and that column defines the order in which the rows are returned from the base tables (that is, a unique indexed column). For example, if Adaptive Server accesses a base table using an index, and the index key is updated by the client, the updated index row can move within the index and be read again by the cursor. The row seems to appear twice in the result set: when the index key is updated by the client and when the updated index row moves farther down the result set. Another way to avoid the Halloween problem is to create tables with the unique auto_identity index database option set to on. See the System Administration Guide for more information.Opening cursors 604 Adaptive Server Enterprise Opening cursors After you declare a cursor, you must open it to fetch, update, or delete rows. Opening a cursor lets Adaptive Server begin to create the cursor result set by evaluating the select statement that defines the cursor and makes it available for processing. The syntax for the open statement is: open cursor_name You cannot open a cursor that is already open or that has not been defined with the declare cursor statement. You can reopen a closed cursor to reset the cursor position to the beginning of the cursor result set. Fetching data rows using cursors A fetch completes the cursor result set and returns one or more rows to the client that is responsible for extracting the column data from the row. Depending on the type of query defined in the cursor, Adaptive Server creates the cursor result set either by scanning the tables directly or by scanning a worktable generated by the query type. The fetch command positions the cursor before the first row of the cursor result set. If the table has a valid index, Adaptive Server positions the cursor at the first index key. Optionally, you can include Transact-SQL parameters or local variables with fetch to store column values. fetch syntax The syntax for the fetch statement is: fetch cursor_name [into fetch_target_list] After generating the cursor result set, Adaptive Server moves the cursor position one or more rows down the result set. It retrieves the data from each row of the result set and stores the current position, allowing additional fetches until Adaptive Server reaches the end of the result set. For example, after declaring and opening the authors_crsr cursor, you can fetch the first row of its result set as follows: fetch authors_crsrCHAPTER 18 Cursors: Accessing Data Row by Row Transact-SQL User’s Guide 605 au_id au_lname au_fname ----------- ------------------- --------------- 341-22-1782 Smith Meander (1 row affected) Each subsequent fetch retrieves another row from the cursor result set. For example: fetch authors_crsr au_id au_lname au_fname ----------- ------------------- --------------- 527-72-3246 Greene Morningstar (1 row affected) After you fetch all the rows, the cursor points to the last row of the result set. If you fetch again, Adaptive Server returns a warning through the @@sqlstatus variable (described under “Checking the cursor status” on page 605) indicating there is no more data. The cursor position remains unchanged. You cannot fetch a row that has already been fetched. Close and reopen the cursor to generate the cursor result set again and start fetching from the beginning. The into clause specifies that Adaptive Server returns column data into the specified variables. The fetch_target_list must consist of previously declared Transact-SQL parameters or local variables. For example, after declaring the @name, @city, and @state variables, you can fetch rows from the pubs_crsr cursor as follows: fetch pubs_crsr into @name, @city, @state Adaptive Server expects a one-to-one correspondence between the variables in the fetch_target_list and the target list expressions specified by the select_statement that defines the cursor. The datatypes of the variables or parameters must be compatible with the datatypes of the columns in the cursor result set. Checking the cursor status Adaptive Server returns a status value after each fetch. You can access the value through the global variable @@sqlstatus. Table 18-1lists @@sqlstatus values and their meanings: Fetching data rows using cursors 606 Adaptive Server Enterprise Table 18-1: @@sqlstatus values The following example determines the @@sqlstatus for the currently open authors_crsr cursor: select @@sqlstatus --------- 0 (1 row affected) Only a fetch statement can set @@sqlstatus. Other statements have no effect on @@sqlstatus. Getting multiple rows with each fetch By default, fetch retrieves only one row at a time. You can use the cursor rows option of the set command to change the number of rows that are returned by fetch. However, this option does not affect a fetch containing an into clause. The syntax for set is: set cursor rows number for cursor_name number specifies the number of rows for the cursor. The number can be a numeric literal with no decimal point, or a local variable of type integer. The default setting is 1 for each cursor you declare. You can set the cursor rows option for any cursor whether it is open or closed. For example, you can change the number of rows fetched for the authors_crsr cursor as follows: set cursor rows 3 for authors_crsr After you set the number of cursor rows, each fetch of authors_crsr returns three rows from the cursor result set: fetch authors_crsr au_id au_lname au_fname Value Meaning 0 Indicates successful completion of the fetch statement. 1 Indicates that the fetch statement resulted in an error. 2 Indicates that there is no more data in the result set. This warning can occur if the current cursor position is on the last row in the result set and the client submits a fetch statement for that cursor.CHAPTER 18 Cursors: Accessing Data Row by Row Transact-SQL User’s Guide 607 ----------- ------------------- --------------- 648-92-1872 Blotchet-Halls Reginald 712-45-1867 del Castillo Innes 722-51-5424 DeFrance Michel (3 rows affected) The cursor is positioned on the last row fetched (the author Michel DeFrance in the example). Fetching several rows at a time works especially well for client applications. If you fetch more than one row, Open Client or Embedded SQL buffers the rows sent to the client application. The client still sees a row-by-row access, but each fetch results in fewer calls to Adaptive Server, which improves performance. Checking the number of rows fetched Use the @@rowcount global variable to monitor the number of rows of the cursor result set returned to the client up to the last fetch. This variable displays the total number of rows seen by the cursor at any one time. Once all the rows are read from a cursor result set, @@rowcount represents the total number of rows in that result set. Each open cursor is associated with a specific @@rowcount variable. The variable is dropped when you close the cursor. Checking @@rowcount after a fetch provides you with the number of rows read for the cursor specified in that fetch. The following example determines the @@rowcount for the currently open authors_crsr cursor: select @@rowcount --------- 5 (1 row affected)Updating and deleting rows using cursors 608 Adaptive Server Enterprise Updating and deleting rows using cursors If the cursor is updatable, use the update or delete statement to update or delete rows. Adaptive Server determines whether the cursor is updatable by checking the select_statement that defines the cursor. You can also explicitly define a cursor as updatable with the for update clause of the declare cursor statement. See “Making cursors updatable” on page 601 for more information. Updating cursor result set rows You can use the where current of clause of the update statement to update the row at the current cursor position. Any update to the cursor result set also affects the base table row from which the cursor row is derived. The syntax for update...where current of is: update [[database.]owner.] {table_name | view_name} set [[[database.]owner.] {table_name. | view_name.}] column_name1 = {expression1 | NULL | (select_statement)} [, column_name2 = {expression2 | NULL | (select_statement)}]... where current of cursor_name The set clause specifies the cursor’s result set column name and assigns the new value. When more than one column name and value pair is listed, you must separate them with commas. The table_name or view_name must be the table or view specified in the first from clause of the select statement that defines the cursor. If that from clause references more than one table or view (using a join), you can specify only the table or view actually being updated. For example, you can update the row that the pubs_crsr cursor currently points to as follows: update publishers set city = "Pasadena", state = "CA" where current of pubs_crsr After the update, the cursor position remains unchanged. You can continue to update the row at that cursor position, as long as another SQL statement does not move the position of that cursor.CHAPTER 18 Cursors: Accessing Data Row by Row Transact-SQL User’s Guide 609 Adaptive Server allows you to update columns that are not specified in the list of columns of the cursor’s select_statement, but are part of the tables specified in that statement. However, when you specify a column_name_list with for update, you can update only the columns in that list. Deleting cursor result set rows Using the where current of clause of the delete statement, you can delete the row at the current cursor position. When you delete a row from the cursor’s result set, the row is deleted from the underlying database table. You can delete only one row at a time using the cursor. The syntax for delete...where current of is: delete [from] [[database.]owner.] {table_name | view_name} where current of cursor_name The table_name or view_name specified with a delete...where current of must be the table or view specified in the first from clause of the select statement that defines the cursor. For example, you can delete the row that the authors_crsr cursor currently points to by entering: delete from authors where current of authors_crsr The from keyword in the above example is optional. Note You cannot delete a row from a cursor defined by a select statement containing a join, even if the cursor is updatable. After you delete a row from a cursor, Adaptive Server positions the cursor before the row following the deleted row in the cursor result set. You must still use fetch to access that next row. If the deleted row is the last row in the cursor result set, Adaptive Server positions the cursor after the last row of the result set. For example, after deleting the current row in the above example (the author Michel DeFrance), you can fetch the next three authors in the cursor result set (assuming that cursor rows is still set to 3): fetch authors_crsrClosing and deallocating cursors 610 Adaptive Server Enterprise au_id au_lname au_fname ----------- ------------------- --------------- 807-91-6654 Panteley Sylvia 899-46-2035 Ringer Anne 998-72-3567 Ringer Albert (3 rows affected) You can, of course, delete a row from the base table without referring to a cursor. The cursor result set changes as changes are made to the base table. Closing and deallocating cursors When you are finished with the result set of a cursor, you can close it using: close cursor_name Closing the cursor does not change its definition. If you reopen a cursor Adaptive Server creates a new cursor result set using the same query as before. For example: close authors_crsr open authors_crsr You can then fetch from authors_crsr, starting from the beginning of its cursor result set. Any conditions associated with that cursor (such as the number of rows fetched defined by set cursor rows) remain in effect. For example: fetch authors_crsr au_id au_lname au_fname ----------- ------------------- --------------- 341-22-1782 Smith Meander 527-72-3246 Greene Morningstar 648-92-1872 Blotchet-Halls Reginald (3 rows affected) To discard a cursor, you must deallocate it using: deallocate cursor cursor_nameCHAPTER 18 Cursors: Accessing Data Row by Row Transact-SQL User’s Guide 611 Deallocating a cursor frees up any resources associated with the cursor, including the cursor name. You cannot reuse a cursor name until you deallocate it. If you deallocate an open cursor, Adaptive Server automatically closes it. Terminating a client connection to a server also closes and deallocates any open cursors. An example using a cursor The following cursor example uses this query: select author = au_fname + " " + au_lname, au_id from authors The results of the query are: author au_id ------------------------- ----------- Johnson White 172-32-1176 Marjorie Green 213-46-8915 Cheryl Carson 238-95-7766 Michael O’Leary 267-41-2394 Dick Straight 274-80-9391 Meander Smith 341-22-1782 Abraham Bennet 409-56-7008 Ann Dull 427-17-2319 Burt Gringlesby 472-27-2349 Chastity Locksley 486-29-1786 Morningstar Greene 527-72-3246 Reginald Blotchet Halls 648-92-1872 Akiko Yokomoto 672-71-3249 Innes del Castillo 712-45-1867 Michel DeFrance 722-51-5454 Dirk Stringer 724-08-9931 Stearns MacFeather 724-80-9391 Livia Karsen 756-30-7391 Sylvia Panteley 807-91-6654 Sheryl Hunter 846-92-7186 Heather McBadden 893-72-1158 Anne Ringer 899-46-2035 Albert Ringer 998-72-3567 (23 rows affected) To use a cursor with the above query:An example using a cursor 612 Adaptive Server Enterprise 1 Declare the cursor. This declare cursor statement defines a cursor using the select statement shown above: declare newauthors_crsr cursor for select author = au_fname + " " + au_lname, au_id from authors for update 2 Open the cursor: open newauthors_crsr 3 Fetch rows using the cursor: fetch newauthors_crsr author au_id ------------------------- ----------- Johnson White 172-32-1176 (1 row affected) You can fetch more than one row at a time by specifying the number of rows with the set command: set cursor rows 5 for newauthors_crsr go fetch newauthors_crsr author au_id ------------------------- ----------- Marjorie Green 213-46-8915 Cheryl Carson 238-95-7766 Michael O’Leary 267-41-2394 Dick Straight 274-80-9391 Meander Smith 341-22-1782 (5 rows affected) Each subsequent fetch brings back five more rows: fetch newauthors_crsr author au_id ------------------------- ----------- Abraham Bennet 409-56-7008 Ann Dull 427-17-2319 Burt Gringlesby 472-27-2349 Chastity Locksley 486-29-1786 Morningstar Greene 527-72-3246CHAPTER 18 Cursors: Accessing Data Row by Row Transact-SQL User’s Guide 613 (5 rows affected) The cursor is now positioned at author Morningstar Greene, the last row of the current fetch. 4 Perform the following update to change the first name of Greene: update authors set au_fname = "Voilet" where current of newauthors_crsr The cursor remains at Ms. Greene’s record until the next fetch. 5 When you are finished with the cursor, you can close it: close newauthors_crsr If you open the cursor again, Adaptive Server reruns the query and places the cursor before the first row in the result set. The cursor is still set to return five rows with each fetch. 6 Use the deallocate command to remove the cursor: deallocate cursor newauthors_crsr You cannot reuse a cursor name until you deallocate it. Using cursors in stored procedures Cursors are particularly useful in stored procedures. They allow you to use only one query to accomplish a task that would otherwise require several queries. However, all cursor operations must execute within a single procedure. A stored procedure cannot open, fetch, or close a cursor that was not declared in the procedure. Cursors are undefined outside of the scope of the stored procedure. See “Cursor scope” on page 598. For example, the stored procedure au_sales checks the sales table to see if any books by a particular author have sold well. It uses a cursor to examine each row, and then prints the information. Without the cursor, it would need several select statements to accomplish the same task. Outside stored procedures, you cannot include other statements with declare cursor in the same batch. create procedure au_sales (@author_id id) asUsing cursors in stored procedures 614 Adaptive Server Enterprise /* declare local variables used for fetch */ declare @title_id tid declare @title varchar(80) declare @ytd_sales int declare @msg varchar(120) /* declare the cursor to get each book written by given author */ declare author_sales cursor for select ta.title_id, t.title, t.total_sales from titleauthor ta, titles t where ta.title_id = t.title_id and ta.au_id = @author_id open author_sales fetch author_sales into @title_id, @title, @ytd_sales if (@@sqlstatus = 2) begin print "We do not sell books by this author." close author_sales return end /* if cursor result set is not empty, then process each row of information */ while (@@sqlstatus = 0) begin if (@ytd_sales = NULL) begin select @msg = @title + " -- Had no sales this year." print @msg end else if (@ytd_sales < 500) begin select @msg = @title + " -- Had poor sales this year." print @msg end else if (@ytd_sales < 1000) begin select @msg = @title + " -- Had mediocre sales this year."CHAPTER 18 Cursors: Accessing Data Row by Row Transact-SQL User’s Guide 615 print @msg end else begin select @msg = @title + " -- Had good sales this year." print @msg end fetch author_sales into @title_id, @title, @ytd_sales end For example: au_sales "172-32-1176" Prolonged Data Deprivation: Four Case Studies -- Had good sales this year. (return status = 0) For more information about stored procedures, see Chapter 15, “Using Stored Procedures.” See also the Performance and Tuning Guide for information about how stored procedures that use cursors affect performance. Cursors and locking Cursor locking methods are similar to other locking methods for Adaptive Server. In general, statements that read data (such as select or readtext) use shared locks on each data page to avoid reading changed data from an uncommitted transaction. Update statements use exclusive locks on each page they change. To reduce deadlocks and improve concurrency, Adaptive Server often precedes an exclusive lock with an update lock, which indicates that the client intends to change data on the page.Cursors and locking 616 Adaptive Server Enterprise For updatable cursors, Adaptive Server uses update locks by default when scanning tables or views referenced with the for update clause of declare cursor. If the for update clause is included, but the list is empty, all tables and views referenced in the from clause of the select_statement receive update locks by default. If the for update clause is not included, the referenced tables and views receive shared locks. You can use shared locks instead of update locks by adding the shared keyword to the from clause after each table name for which you prefer a shared lock. Note Adaptive Server releases an update lock when the cursor position moves off the data page. Since an application buffers rows for client cursors, the corresponding server cursor may be positioned on a different data row and page than the client cursor. In this case, a second client could update the row that represents the current cursor position of the first client, even if the first client used the for update option. Any exclusive locks acquired by a cursor in a transaction are held until the end of that transaction. This also applies to shared or update locks when you use the holdlock keyword or the set isolation level 3 option. However, if you do not set the close on endtran option, the cursor remains open past the end of the transaction, and its current page lock remains in effect. It can also continue to acquire locks as it fetches additional rows. For more information about cursor locking in Adaptive Server, see the Performance and Tuning Guide. Cursor locking options These are the effects of specifying the holdlock or shared options (of the select statement) when you define an updatable cursor: • If you omit both options, you can read data on the currently fetched pages only. Other users cannot update your currently fetched pages, through a cursor or otherwise. Other users can declare a cursor on the same tables you use for your cursor, but they cannot get an update lock on your currently fetched pages. • If you specify the shared option, you can read data on the currently fetched pages only. Other users cannot update your currently fetched pages, through a cursor or otherwise.CHAPTER 18 Cursors: Accessing Data Row by Row Transact-SQL User’s Guide 617 • If you specify the holdlock option, you can read data on all pages fetched (in a current transaction) or only the pages currently fetched (if not in a transaction). Other users cannot update your currently fetched pages or pages fetched in your current transaction, through a cursor or otherwise. Other users can declare a cursor on the same tables you use for your cursor, but they cannot get an update lock on your currently fetched pages or the pages fetched in your current transaction. • If you specify both options, you can read data on all pages fetched (in a current transaction) or only the pages currently fetched (if not in a transaction). Other users cannot update your currently fetched pages, through a cursor or otherwise. Getting information about cursors Use sp_cursorinfo to find information about a cursor’s name, its current status, and its result columns. This example displays information authors_crsr: sp_cursorinfo 0, authors_crsr Cursor name ’authors_crsr’ is declared at nesting level ’0’. The cursor id is 327681 The cursor has been successfully opened 1 times The cursor was compiled at isolation level 1. The cursor is not open. The cursor will remain open when a transaction is committed or rolled back. The number of rows returned for each FETCH is 1. The cursor is updatable. There are 3 columns returned by this cursor. The result columns are: Name = ’au_id’, Table = ’authors’, Type = ID, Length = 11 (updatable) Name = ’au_lname’, Table = ’authors’, Type = VARCHAR, Length = 40 (updatable) Name = ’au_fname’, Table = ’authors’, Type = VARCHAR, Length = 20 (updatable) You can also check the status of a cursor using the @@sqlstatus and @@rowcount global variables. See “Checking the cursor status” on page 605 and “Checking the number of rows fetched” on page 607.Using browse mode instead of cursors 618 Adaptive Server Enterprise For more information about sp_cursorinfo, see the Reference Manual. Using browse mode instead of cursors Browse mode lets you search through a table and update its values one row at a time. It is used in front-end applications that use DB-Library and a host programming language. Browse mode is useful because it provides compatibility with Open Server™ applications and older Open Client libraries. However, its use in more recent Client-Library™ applications (release 10.0.x and later) is discouraged, because cursors provide the same functionality in a more portable and flexible manner. Additionally, because browse mode is Sybase-specific, it is not suited to heterogeneous environments. Normally, you should use cursors to update data when you want to change table values row by row. Client-Library applications can use ClientLibrary cursors to implement some browse-mode features, such as updating a table while fetching rows from it. However, cursors may cause locking contention in the tables being selected. For more information on browse mode, see the dbqual function in the Open Client/Server™ documentation. Browsing a table To browse a table in a front-end application, append the for browse keywords to the end of the select statement sent to Adaptive Server. For example: Start of select statement in an Open Client application ... for browse Completion of the Open Client application routine A table can be browsed in a front-end application if its rows have been timestamped.CHAPTER 18 Cursors: Accessing Data Row by Row Transact-SQL User’s Guide 619 Browse-mode restrictions You cannot use the for browse clause in statements involving the union operator, or in cursor declarations. The keyword holdlock is forbidden in a select statement that includes the for browse option. The keyword distinct in the select statement is ignored in browse mode. Timestamping a new table for browsing When creating a new table for browsing, include a column named timestamp in the table definition. This column is automatically assigned the timestamp datatype; you do not have to specify its datatype. For example: create table newtable(col1 int, timestamp, col3 char(7)) Whenever you insert or update a row, Adaptive Server timestamps it by automatically assigning a unique varbinary value to the timestamp column. Timestamping an existing table To prepare an existing table for browsing, add a column named timestamp with alter table. For example: alter table oldtable add timestamp A timestamp column with a null value is added to each existing row. To generate a timestamp, update each row without specifying new column values. For example: update oldtable set col1 = col1Join cursor processing and data modifications 620 Adaptive Server Enterprise Comparing timestamp values Use the tsequal system function to compare timestamps when you are using browse mode in a front-end application. For example, the following statement updates a row in publishers that has been browsed. It compares the timestamp column in the browsed version of the row with the hexadecimal timestamp in the stored version. If the two timestamps are not equal, you receive an error message, and the row is not updated. update publishers set city = "Springfield" where pub_id = "0736" and tsequal(timestamp,0x0001000000002ea8) Do not use the tsequal function in the where clause as a search argument. When you use tsequal, the rest of the where clause should match a single row uniquely. Use the tsequal function only in insert and update statements. If a timestamp column is used as a search clause, it should be compared like a regular varbinary column, that is, timestamp1 = timepstamp2. Join cursor processing and data modifications This section describes changes to cursor behavior, beginning with version 11.9.2, that may affect applications that use cursors. It also describes cursor positioning and modification rules for cursors on data-only-locked tables. Updates and deletes that can affect the cursor position Two types of deletes and updates can affect the row at the cursor position: • Positioned deletes and updates, using delete...where current of or update...where current of to change the row at the cursor position • Searched deletes and updates, that is, any delete or update query that changes a value in the row at the cursor position, but without including a where current of clauseCHAPTER 18 Cursors: Accessing Data Row by Row Transact-SQL User’s Guide 621 Cursor positioning after a delete or update command without joins The behavior of a delete or update command to the base table for a cursor on a single-table query depends on the type of modification, the locking scheme of the base table, and whether the clustered index of the base table is affected: • A positioned delete or a searched delete that deletes the row at the cursor location positions the cursor to the next qualifying row on the table. This is true for both allpages-locked and data-only-locked tables. A subsequent positioned update or delete via this cursor is disallowed until the next fetch is done to position the cursor on the next row that qualifies. • A searched or positioned update that does not change the position of the row leaves the current position of the cursor unchanged. The next fetch returns the next qualifying row. • A searched or positioned update on an allpages-locked table can change the location of the row; for example, if it updates key columns of a clustered index. The cursor does not track the row; it remains positioned just before the next row at the original location. Positioned updates are not allowed until a subsequent fetch returns the next row. The updated row may be visible to the cursor a second time, if the row moves to a later position in the search order. Data-only-locked tables have fixed row IDs, so expanding updates or updates that affect the clustered key do not move the location of the row. The cursor remains positioned on the row, and the next fetch returns the next qualifying row. The cursor positioning behavior described above is unchanged from previous releases. Effects of updates and deletes on join cursors When a searched or positioned delete is issued on the row at the cursor position of a cursor that includes a join, there can be one of two results: • Searched deletes close the cursor implicitly. The next fetch returns error 582: Cursor ’cursor_name’ was closed implicitly because the current cursor position was deleted due to an update or a delete. The cursor scan Join cursor processing and data modifications 622 Adaptive Server Enterprise position could not be recovered. This happens for cursors which reference more than one table. • Positioned deletes fail, with error 592: The DELETE WHERE CURRENT OF to the cursor ’cursor_name’ failed because the cursor is on a join. The cursor remains open, positioned at the same row. When a searched or positioned update is issued on the join columns of a cursor: • Searched updates to clustered index keys on allpages-locked tables succeed, but implicitly close the cursor, so the next fetch returns error 582. Searched updates to clustered index keys do not close cursors on data-only-locked tables. • Positioned updates for all locking schemes, and searched updates that do not change a clustered index key on an allpages-locked table succeed and do not close the cursor. The cursor position depends on the type of table and whether the column has a clustered index. See “Cursor positioning after a delete or update command without joins” on page 621 for more information. Join column buffering may affect the result sets returned when join columns are updated. See “Join cursor processing and data modifications” on page 620 for more information. Table 18-2 shows how delete and update commands affect join cursors. In this table, “Left open” means that the cursor is not closed by the update. The cursor is still positioned on the row, so positioned updates can still be made, and the next fetch also succeeds. Table 18-2: Effects of deletes and join column updates in join cursors Allpages-locked Data-only-locked delete commands Positioned direct delete Error 592 Error 592 Searched direct delete Error 582 Error 582 Searched deferred delete Error 582 Error 582 Searched delete affecting clustered index (deferred) Error 582 Error 582 update commands Positioned direct update Left open Left openCHAPTER 18 Cursors: Accessing Data Row by Row Transact-SQL User’s Guide 623 Effects of join column buffering on join cursors For cursors on queries that include joins, the join columns, search arguments and select list values for the outer table in the join order are buffered with the first fetch. If more than one row is returned from the inner table in the join order, subsequent fetches use the buffered value for the outer row. This means that the behavior of applications that update join columns and search arguments through cursors can vary, depending on the join order chosen for the query. Join column buffering affects both allpages-locked tables and data-only-locked tables. Note In version 11.5.x, join cursors on allpages-locked tables did not buffer join values. Effects of column buffering during cursor scans The results of cursor queries that perform joins may produce varying results, depending on the join order chosen for the query, if updates to the join column take place during the session. The following two examples illustrate how join order can affect cursor results sets. select * from dept dept_id deptloc ------- ----------------- 1 Elm Street 2 Acacia Drive 3 Maple Lane 4 Oak Avenue select * from employee dept_id empid ------- --------- 1 172321176 1 213468915 2 341221782 2 409567008 Searched direct update Left open Left open Searched deferred update Left open Left open Searched update affecting clustered index (deferred) Error 582 Left open Allpages-locked Data-only-lockedJoin cursor processing and data modifications 624 Adaptive Server Enterprise 2 427172319 3 472272349 3 486291786 Example of join column buffering These statements declare a cursor, open it, and fetch the first row: declare j_curs cursor for select d.dept_id, e.empid, d.deptloc from dept d , employee e where d.dept_id = e.dept_id and d.dept_id = 2 open j_curs fetch j_curs dept_id empid deptloc ----------- ----------- -------------------- 2 341221782 Acacia Drive If dept is chosen as the outer column in the join order, the value 2 for dept_id is buffered. The following update changes the dept_id of the join column in dept: update dept set dept_id = 12 where current of j_curs This update changes the value stored in the table row, but does not alter the buffered value, hiding the result of this update to the base table from the cursor. The effect would be the same if the join column in dept were updated by a non-positioned update. This update changes the dept_id of the employee row: update employee set dept_id = 12 where current of j_curs The next fetch on the table returns the second row in the result set: fetch j_curs dept_id empid deptloc ----------- ----------- -------------------- 2 409567008 Acacia Drive All matching rows from employee can be fetched and updated. If the join order for this cursor selects employee as the outer table, and the join column in dept is updated after the first fetch, the second fetch finds no matching rows. This is the sequence of steps: 1 The value 2 for employee.dept_id is buffered during the first fetch.CHAPTER 18 Cursors: Accessing Data Row by Row Transact-SQL User’s Guide 625 2 A searched or positioned update changes the value of dept.dept_id to 12. 3 At the second fetch, 2, the buffered value for employee.dept_id is used, and the inner table is scanned for matching values; since dept.dept_id has been changed to 12, the second fetch does not return a row. The two remaining rows in employee with dept_id equal to 2 cannot be fetched by the cursor. Example of search argument buffering Due to buffering of search arguments, the sensitivity of cursor results to updates of the search arguments on cursor select queries also depends on join order. This example uses the dept and employee tables as shown in “Effects of column buffering during cursor scans” on page 623. The following cursor joins on the dept_id columns of the table, using a search argument on the deptloc column: declare c cursor for select d.dept_id, empid, deptloc from dept d , employee e where d.dept_id = e.dept_id and deptloc = "Acacia Drive" The first fetch on this table returns this row: dept_id empid deptloc --------- ----------- -------------- 2 41221782 Acacia Drive This positioned update statement changes employee.dept_id value to 4 for the current row; it needs to be performed for each employee in the department located at Acacia Drive: update employee set dept_id = 4 where current of c This positioned update changes the dept.deptloc value from “Acacia Drive” to “Pine Way”, update dept set deptloc = "Pine Way" where current of c If the update to deptloc is issued after the first fetch, the result set may or may not return all of the rows that need to be changed; the results depend on the join order chosen for the query:Join cursor processing and data modifications 626 Adaptive Server Enterprise • If dept is chosen as the outer table, the dept.dept_id and dept.deptloc columns, the values “2” and “Acacia Drive”, are buffered. After the first fetch, the update to deptloc updates the base table, but not the buffered values, and subsequent fetch commands return additional result set rows. • If employee is chosen as the outer table, only the dept_id qualification on the employee table is buffered. The update to the deptloc column changes the base table, and when the search argument qualification “Acacia Drive” is applied to the deptloc table at the next fetch, no rows are returned, even though two rows with employee.dept_id of 2 remain in the table. Note that issuing the update to deptloc after all rows from the employee table have been fetched would accomplish both updates, without a dependency on the join order. Effects of select-list buffering Columns from the select list of the outer table in the join order are buffered when a row from the outer table is fetched. If a searched or positioned update is performed on a column in the select list, and another row is fetched from the inner table, the buffered value from the outer table appears in the cursor result row. Recommendations In general, applications should attempt to avoid updating join columns or columns with search clauses and other predicates to change their value when cursor scans are in progress. • Avoid updates to the join columns of cursors or to the search arguments of join cursors whenever possible, unless you are completely sure of the join order. • Use a cursor query that creates a worktable, and then use searched updates and deletes on the base table. When a cursor select query requires a worktable, the cursor is always insensitive to changes to the underlying table. Cursors that include order by, distinct, group by, or other clauses that create a worktable cannot be updated with positioned updates.CHAPTER 18 Cursors: Accessing Data Row by Row Transact-SQL User’s Guide 627 • If you are using cursors to update both join columns, consider using searched updates instead of positioned updates. Although further fetches may return buffered values instead of values that have been changed in the data rows, use of searched updates avoids the possibility of failing to fetch matching rows due to the choice of join order. Searched updates to a clustered index key in an allpages-locked table implicitly close the cursor. • Note that the ANSI SQL 92 entry-level specification does not allow updates to join columns using cursors, so the behavior is implementation-specific. Applications designed to be portable across different database software must take individual implementations into account.Join cursor processing and data modifications 628 Adaptive Server EnterpriseTransact-SQL User’s Guide 629 C H A P T E R 1 9 Transactions: Maintaining Data Consistency and Recovery A transaction groups a set of Transact-SQL statements so that they are treated as a unit. Either all statements in the group are executed or no statements are executed. This chapter discusses: For more information about transactions, see the Performance and Tuning Guide. How transactions work Adaptive Server automatically manages all data modification commands, including single-step change requests, as transactions. By default, each insert, update, and delete statement is considered a single transaction. However, consider the following scenario: Lee needs to make a series of data retrievals and modifications to the authors, titles, and titleauthors tables. As she is doing so, Lil begins to update the titles table. Lil’s updates could cause inconsistent results with the work that Lee is doing. To prevent this from happening, Lee can group her statements into a single transaction, which locks Lil out of the portions of the tables that Lee is working on. This allows Lee to complete her work based on accurate data. After she completes her table updates, Lil’s updates can take place. Topic Page How transactions work 629 Using transactions 633 Selecting the transaction mode and isolation level 641 Using transactions in stored procedures and triggers 654 Using cursors in transactions 662 Issues to consider when using transactions 663 Backup and recovery of transactions 664How transactions work 630 Adaptive Server Enterprise You can use the following commands to create transactions: • begin transaction – marks the beginning of the transaction block. The syntax is: begin {transaction | tran} [transaction_name] transaction_name is the name assigned to the transaction. It must conform to the rules for identifiers. Use transaction names only on the outermost pair of nested begin/commit or begin/rollback statements. • save transaction – marks a savepoint within a transaction: save {transaction | tran} savepoint_name savepoint_name is the name assigned to the savepoint. It must conform to the rules for identifiers. • commit – commits the entire transaction: commit [transaction | tran | work] [transaction_name] • rollback – rolls a transaction back to a savepoint or to the beginning of a transaction: rollback [transaction | tran | work] [transaction_name | savepoint_name] For example, user Lee sets out to change the royalty split for two authors of The Gourmet Microwave. Since the database would be inconsistent between the two updates, they must be grouped into a transaction, as shown in the following example: begin transaction royalty_change update titleauthor set royaltyper = 65 from titleauthor, titles where royaltyper = 75 and titleauthor.title_id = titles.title_id and title = "The Gourmet Microwave" update titleauthor set royaltyper = 35 from titleauthor, titles where royaltyper = 25 and titleauthor.title_id = titles.title_id and title = "The Gourmet Microwave" CHAPTER 19 Transactions: Maintaining Data Consistency and Recovery Transact-SQL User’s Guide 631 save transaction percentchanged /* After updating the royaltyper entries for ** the two authors, insert the savepoint ** percentchanged, then determine how a 10% ** increase in the book’s price would affect ** the authors’ royalty earnings. */ update titles set price = price * 1.1 where title = "The Gourmet Microwave" select (price * total_sales) * royaltyper from titles, titleauthor where title = "The Gourmet Microwave" and titles.title_id = titleauthor.title_id /* The transaction is rolled back to the savepoint ** with the rollback transaction command. */ rollback transaction percentchanged commit transaction Transactions allow Adaptive Server to guarantee: • Consistency – simultaneous queries and change requests cannot collide with each other, and users never see or operate on data that is partially through a change. • Recovery – in case of system failure, database recovery is complete and automatic. To support SQL standards-compliant transactions, Adaptive Server allows you to select the mode and isolation level for your transactions. Applications that require SQL standards-compliant transactions should set those options at the beginning of every session. Transaction modes and isolation levels are described later in this chapter. See “Selecting the transaction mode and isolation level” on page 641 for more information.How transactions work 632 Adaptive Server Enterprise Transactions and consistency In a multiuser environment, Adaptive Server must prevent simultaneous queries and data modification requests from interfering with each other. This is important because if the data being processed by a query can be changed by another user’s update, the results of the query may be ambiguous. Adaptive Server automatically sets the appropriate level of locking for each transaction. You can make shared locks more restrictive on a query-by-query basis by including the holdlock keyword in a select statement. Transactions and recovery A transaction is both a unit of work and a unit of recovery. The fact that Adaptive Server handles single-step change requests as transactions means that the database can be recovered completely in case of failure. Adaptive Server’s recovery time is measured in minutes and seconds. You can specify the maximum acceptable recovery time. The SQL commands related to recovery and backup are discussed in “Backup and recovery of transactions” on page 664. Note Grouping large numbers of Transact-SQL commands into one longrunning transaction may affect recovery time. If Adaptive Server fails before the transaction commits, recovery takes longer, because Adaptive Server must undo the transaction. If you are using a remote database with Component Integration Services, there are a few differences in the way transactions are handled. See the Component Integration Services User’s Guide for more information. If you have purchased and installed Adaptive Server DTM features, transactions that update data in multiple servers can also benefit from transactional consistency. See Using Adaptive Server Distributed Transaction Features for more information.CHAPTER 19 Transactions: Maintaining Data Consistency and Recovery Transact-SQL User’s Guide 633 Using transactions The begin transaction and commit transaction commands tell Adaptive Server to process any number of individual commands as a single unit. rollback transaction undoes the transaction, either back to its beginning, or back to a savepoint. You define a savepoint inside a transaction using save transaction. Transactions give you control over transaction management. In addition to grouping SQL statements to behave as a single unit, they improve performance, since system overhead is incurred once per transaction, rather than once for each individual command. Any user can define a transaction. No permission is required for any of the transaction commands. The following sections discuss general transaction topics and transaction commands, with examples. Allowing data definition commands in transactions You can use certain data definition language commands in transactions by setting the ddl in tran database option to true. If ddl in tran is true in a particular database, you can issue commands such as create table, grant, and alter table inside transactions in that database. If ddl in tran is true in the model database, you can issue the commands inside transactions in all databases created after ddl in tran was set to true in model. To check the current settings of ddl in tran, use sp_helpdb. Warning! Be careful when using data definition commands. The only scenario in which using data definition language commands inside transactions is justified is in create schema. Data definition language commands hold locks on system tables such as sysobjects. If you use data definition language commands inside transactions, keep the transactions short. Avoid using data definition language commands on tempdb within transactions; doing so can slow performance to a halt. Always leave ddl in tran set to false in tempdb. To set ddl in tran to true, enter: sp_dboption database_name,"ddl in tran", true Then execute the checkpoint command in that database.Using transactions 634 Adaptive Server Enterprise The first parameter specifies the name of the database in which to set the option. You must be using the master database to execute sp_dboption. Any user can execute sp_dboption with no parameters to display the current option settings. To set options, however, you must be either a System Administrator or the Database Owner. The following commands are allowed inside a transaction only if the ddl in tran option to sp_dboption is set to true: Table 19-1: DDL commands allowed in transactions System procedures that change the master database or create temporary tables cannot be used inside transactions. Never use the following commands inside a transaction: Table 19-2: DDL commands not allowed in transactions System procedures that are not allowed in transactions You cannot use the following system procedures within transactions: • sp_helpdb, sp_helpdevice, sp_helpindex, sp_helpjoins, sp_helpserver, sp_lookup, and sp_spaceused (because they create temporary tables) • sp_configure • System procedures that change the master database alter table (you cannot issue the alter table command with a partition or unpartition clause within a userdefined transaction) create default create index create procedure create rule create schema create table create trigger create view drop default drop index drop procedure drop rule drop table drop trigger drop view grant revoke alter database alter table...partition alter table...unpartition create database disk init dump database dump transaction drop database load transaction load database reconfigure select into update statistics truncate tableCHAPTER 19 Transactions: Maintaining Data Consistency and Recovery Transact-SQL User’s Guide 635 Beginning and committing transactions The begin transaction and commit transaction commands can enclose any number of SQL statements and stored procedures. The syntax for both statements is: begin {transaction | tran} [transaction_name] commit {transaction | tran | work} [transaction_name] transaction_name is the name assigned to the transaction. It must conform to the rules for identifiers. The keywords transaction, tran, and work (in commit transaction) are synonymous; you can use one in the place of the others. However, transaction and tran are Transact-SQL extensions; only work is SQL standards-compliant. Here is a skeletal example: begin tran statement procedure statement commit tran commit transaction does not affect Adaptive Server if the transaction is not currently active. Rolling back and saving transactions If you must cancel a transaction before it commits—either because of some failure or because of a change by the user—you must undo all of its completed statements or procedures. Refer to Table 19-4 on page 658 for the effects of rollback during processing. You can cancel or roll back a transaction with the rollback transaction command any time before commit transaction has been given. Using savepoints, you can cancel either an entire transaction or part of it. However, you cannot cancel a transaction after it has been committed. The syntax of rollback transaction is: rollback {transaction | tran | work} [transaction_name | savepoint_name] Using transactions 636 Adaptive Server Enterprise A savepoint is a marker that the user puts inside a transaction to indicate a point to which it can be rolled back. You can commit only certain portions of a batch by rolling back the undesired portion to a savepoint before committing the entire batch. You can insert a savepoint by putting a save transaction command in the transaction. The syntax is: save {transaction | tran} savepoint_name The savepoint name must conform to the rules for identifiers. If no savepoint_name or transaction_name is given with rollback transaction, the transaction is rolled back to the first begin transaction in a batch. Here is how you can use the save transaction and rollback transaction commands: begin tran statements Group A save tran mytran statements Group B rollback tran mytran Rolls back group B statements Group C commit tran Commits groups A and C Until you issue a commit transaction, Adaptive Server considers all subsequent statements to be part of the transaction, unless it encounters another begin transaction statement. At that point, Adaptive Server considers all subsequent statements to be part of the new, nested transaction. Nested transactions are described under “Nested transactions” on page 639. rollback transaction or save transaction does not affect Adaptive Server and does not return an error message if the transaction is not currently active. You can also use save transaction to create transactions in stored procedures or triggers in such a way that they can be rolled back without affecting batches or other procedures. For example: create proc myproc as begin tran save tran mytran statements if ... begin rollback tran mytran /* ** Rolls back to savepoint. */CHAPTER 19 Transactions: Maintaining Data Consistency and Recovery Transact-SQL User’s Guide 637 commit tran /* ** This commit needed; rollback to a savepoint ** does not cancel a transaction. */ end else commit tran /* ** Matches begin tran; either commits ** transaction (if not nested) or ** decrements nesting level. */ Unless you are rolling back to a savepoint, use transaction names only on the outermost pair of begin/commit or begin/rollback statements. Warning! Transaction names are ignored, or can cause errors, when used in nested transaction statements. If you are using transactions in stored procedures or triggers that could be called from within other transactions, do not use transaction names. Checking the state of transactions The global variable @@transtate keeps track of the current state of a transaction. Adaptive Server determines what state to return by keeping track of any transaction changes after a statement executes. @@transtate may contain the following values:Using transactions 638 Adaptive Server Enterprise Table 19-3: @@transtate values Adaptive Server does not clear @@transtate after every statement. In a transaction, you can use @@transtate after a statement (such as an insert) to determine whether it was successful or aborted, and to determine its effect on the transaction. The following example checks @@transtate during a transaction (after a successful insert) and after the transaction commits: begin transaction insert into publishers (pub_id) values ("9999") (1 row affected) select @@transtate ---------- 0 (1 row affected) commit transaction select @@transtate ---------- 1 (1 row affected) The next example checks @@transtate after an unsuccessful insert (due to a rule violation) and after the transaction rolls back: begin transaction insert into publishers (pub_id) values ("7777") Msg 552, Level 16, State 1: A column insert or update conflicts with a rule bound to the column. The command is aborted. The conflict occured in database ’pubs2’, table ’publishers’, rule ’pub_idrule’, column ’pub_id’. select @@transtate ---------- 2 Value Meaning 0 Transaction in progress. A transaction is in effect; the previous statement executed successfully. 1 Transaction succeeded. The transaction completed and committed its changes. 2 Statement aborted. The previous statement was aborted; no effect on the transaction. 3 Transaction aborted. The transaction aborted and rolled back any changes.CHAPTER 19 Transactions: Maintaining Data Consistency and Recovery Transact-SQL User’s Guide 639 (1 row affected) rollback transaction select @@transtate ---------- 3 (1 row affected) Adaptive Server does not clear @@transtate after every statement. It changes @@transtate only in response to an action taken by a transaction. Syntax and compile errors do not affect the value of @@transtate. Nested transactions You can nest transactions within other transactions. When you nest begin transaction and commit transaction statements, the outermost pair actually begin and commit the transaction. The inner pairs just keep track of the nesting level. Adaptive Server does not commit the transaction until the commit transaction that matches the outermost begin transaction is issued. Normally, this transaction “nesting” occurs as stored procedures or triggers that contain begin/commit pairs call each other. The @@trancount global variable keeps track of the current nesting level for transactions. An initial implicit or explicit begin transaction sets @@trancount to 1. Each subsequent begin transaction increments @@trancount, and a commit transaction decrements it. Firing a trigger also increments @@trancount, and the transaction begins with the statement that causes the trigger to fire. Nested transactions are not committed unless @@trancount equals 0. For example, the following nested groups of statements are not committed by Adaptive Server until the final commit transaction: begin tran select @@trancount /* @@trancount = 1 */ begin tran select @@trancount /* @@trancount = 2 */ begin tran select @@trancount /* @@trancount = 3 */ commit tranUsing transactions 640 Adaptive Server Enterprise commit tran commit tran select @@trancount /* @@ trancount = 0 */ When you nest a rollback transaction statement without including a transaction or savepoint name, it rolls back to the outermost begin transaction statement and cancels the transaction. Example of a transaction This example shows how a transaction might be specified: begin transaction royalty_change /* A user sets out to change the royalty split */ /* for the two authors of The Gourmet Microwave. */ /* Since the database would be inconsistent */ /* between the two updates, they must be grouped */ /* into a transaction. */ update titleauthor set royaltyper = 65 from titleauthor, titles where royaltyper = 75 and titleauthor.title_id = titles.title_id and title = "The Gourmet Microwave" update titleauthor set royaltyper = 35 from titleauthor, titles where royaltyper = 25 and titleauthor.title_id = titles.title_id and title = "The Gourmet Microwave" save transaction percent_changed /* After updating the royaltyper entries for */ /* the two authors, the user inserts the */CHAPTER 19 Transactions: Maintaining Data Consistency and Recovery Transact-SQL User’s Guide 641 /* savepoint “percent_changed,” and then checks */ /* to see how a 10 percent increase in the */ /* price would affect the authors’ royalty */ /* earnings. */ update titles set price = price * 1.1 where title = "The Gourmet Microwave" select (price * royalty * total_sales) * royaltyper from titles, titleauthor, roysched where title = "The Gourmet Microwave" and titles.title_id = titleauthor.title_id and titles.title_id = roysched.title_id rollback transaction percent_changed /* The transaction rolls back to the savepoint */ /* with the rollback transaction command. */ /* Without a savepoint, it would roll back to */ /* the begin transaction. */ commit transaction Selecting the transaction mode and isolation level Adaptive Server provides the following options to support SQL standardscompliant transactions: • The transaction mode lets you set whether transactions begin with or without an implicit begin transaction statement. • The isolation level refers to the degree to which data can be accessed by other users during a transaction. Set these options at the beginning of every session that requires SQL standardscompliant transactions. The following sections describe these options in more detail.Selecting the transaction mode and isolation level 642 Adaptive Server Enterprise Choosing a transaction mode Adaptive Server supports the following transaction modes: • The SQL standards-compatible mode, called chained mode, implicitly begins a transaction before any data retrieval or modification statement. These statements include: delete, insert, open, fetch, select, and update. You must still explicitly end the transaction with commit transaction or rollback transaction. • The default mode, called unchained mode or Transact-SQL mode, requires explicit begin transaction statements paired with commit transaction or rollback transaction statements to complete the transaction. You can set either mode using the chained option of the set command. However, do not mix these transaction modes in your applications. The behavior of stored procedures and triggers can vary, depending on the mode, and you may require special action to run a procedure in one mode that was created in the other. The SQL standards require every SQL data-retrieval and data-modification statement to occur inside a transaction, using chained mode. A transaction automatically starts with the first data-retrieval or data-modification statement after the start of a session or after the previous transaction commits or aborts. This is the chained transaction mode. You can set this mode for your current session by turning on the chained option of the set statement: set chained on However, you cannot execute the set chained command within a transaction. To return to the unchained transaction mode, set the chained option to off. The default transaction mode is unchained. In chained transaction mode, Adaptive Server implicitly executes a begin transaction statement just before the following data retrieval or modification statements: delete, insert, open, fetch, select, and update. For example, the following group of statements produce different results, depending on which mode you use: insert into publishers values ("9906", null, null, null) begin transaction delete from publishers where pub_id = "9906" rollback transactionCHAPTER 19 Transactions: Maintaining Data Consistency and Recovery Transact-SQL User’s Guide 643 In unchained transaction mode, the rollback affects only the delete statement, so publishers still contains the inserted row. In chained mode, the insert statement implicitly begins a transaction, and the rollback affects all statements up to the beginning of that transaction, including the insert. All application programs and ad hoc user queries should know their current transaction mode. Which transaction mode you use depends on whether or not a particular query or application requires compliance to the SQL standards. Applications that use chained transactions (for example, the Embedded SQL precompiler) should set chained mode at the beginning of each session. Transaction modes and nested transactions Although chained mode implicitly begins transactions with data retrieval or modification statements, you can nest transactions only by explicitly using begin transaction statements. Once the first transaction implicitly begins, further data retrieval or modification statements no longer begin transactions until after the first transaction commits or aborts. For example, in the following query, the first commit transaction commits all changes in chained mode; the second commit is unnecessary: insert into publishers values ("9907", null, null, null) insert into publishers values ("9908", null, null, null) commit transaction commit transaction Note In chained mode, a data retrieval or modification statement begins a transaction whether or not it executes successfully. Even a select that does not access a table begins a transaction. Finding the status of the current transaction mode You can check the global variable @@tranchained to determine Adaptive Server’s current transaction mode. select @@tranchained returns 0 for unchained mode or 1 for chained mode.Selecting the transaction mode and isolation level 644 Adaptive Server Enterprise Choosing an isolation level The SQL92 standard defines four levels of isolation for transactions. Each isolation level specifies the kinds of actions that are not permitted while concurrent transactions are executing. Higher levels include the restrictions imposed by the lower levels: • Level 0 – ensures that data written by one transaction represents the actual data. It prevents other transactions from changing data that has already been modified (through an insert, delete, update, and so on) by an uncommitted transaction. The other transactions are blocked from modifying that data until the transaction commits. However, other transactions can still read the uncommitted data, which results in dirty reads. • Level 1 – prevents dirty reads. Such reads occur when one transaction modifies a row, and a second transaction reads that row before the first transaction commits the change. If the first transaction rolls back the change, the information read by the second transaction becomes invalid. This is the default isolation level supported by Adaptive Server. • Level 2 – prevents nonrepeatable reads. Such reads occur when one transaction reads a row and a second transaction modifies that row. If the second transaction commits its change, subsequent reads by the first transaction yield different results than the original read. Adaptive Server supports this level for data-only-locked tables. It is not supported for allpages-locked tables. • Level 3 – ensures that data read by one transaction is valid until the end of that transaction, hence preventing phantom rows. Adaptive Server supports this level through the holdlock keyword of the select statement, which applies a read-lock on the specified data. Phantom rows occur when one transaction reads a set of rows that satisfy a search condition, and then a second transaction modifies the data (through an insert, delete, update, and so on). If the first transaction repeats the read with the same search conditions, it obtains a different set of rows. You can set the isolation level for your session by using the transaction isolation level option of the set command. You can enforce the isolation level for just a query as opposed to using the at isolation clause of the select statement. For example: set transaction isolation level 0CHAPTER 19 Transactions: Maintaining Data Consistency and Recovery Transact-SQL User’s Guide 645 Default isolation levels for Adaptive Server and SQL92 By default, the Adaptive Server transaction isolation level is 1. The SQL92 standard requires that level 3 be the default isolation for all transactions. This prevents dirty reads, nonrepeatable reads, and phantom rows. To enforce this default level of isolation, Transact-SQL provides the transaction isolation level 3 option of the set statement. This option instructs Adaptive Server to apply a holdlock to all select operations in a transaction. For example: set transaction isolation level 3 Applications that use transaction isolation level 3 should set that isolation level at the beginning of each session. However, setting transaction isolation level 3 causes Adaptive Server to hold any read locks for the duration of the transaction. If you also use the chained transaction mode, that isolation level remains in effect for any data retrieval or modification statement that implicitly begins a transaction. In both cases, this can lead to concurrency problems for some applications, since more locks may be held for longer periods of time. To return your session to the Adaptive Server default isolation level: set transaction isolation level 1 Dirty reads Applications that are not impacted by dirty reads may have better concurrency and reduced deadlocks when accessing the same data if you set transaction isolation level 0 at the beginning of each session. An example is an application that finds the momentary average balance for all savings accounts stored in a table. Since it requires only a snapshot of the current average balance, which probably changes frequently in an active table, the application should query the table using isolation level 0. Other applications that require data consistency, such as deposits and withdrawals to specific accounts in the table, should avoid using isolation level 0. Scans at isolation level 0 do not acquire any read locks for their scans, so they do not block other transactions from writing to the same data, and vice versa. However, even if you set your isolation level to 0, utilities (like dbcc) and data modification statements (like update) still acquire read locks for their scans, because they must maintain the database integrity by ensuring that the correct data has been read before modifying it. Selecting the transaction mode and isolation level 646 Adaptive Server Enterprise Because scans at isolation level 0 do not acquire any read locks, it is possible that the result set of a level 0 scan may change while the scan is in progress. If the scan position is lost due to changes in the underlying table, a unique index is required to restart the scan. In the absence of a unique index, the scan may be aborted. By default, a unique index is required for a level 0 scan on a table that does not reside in a read-only database. You can override this requirement by forcing Adaptive Server to choose a nonunique index or a table scan, as follows: select * from table_name (index table_name) Activity on the underlying table may abort the scan before completion. Repeatable reads A transaction performing repeatable reads locks all rows or pages read during the transaction. After one query in the transaction has read rows, no other transaction can update or delete the rows until the repeatable-reads transaction completes. However, repeatable-reads transactions do not provide phantom protection by performing range locking, as serializable transactions do. Other transactions can insert values that can be read by the repeatable-reads transaction and can update rows so that they match the search criteria of the repeatable-reads transaction. A transaction performing repeatable reads locks all rows or pages read during the transaction. After one query in the transaction has read rows, no other transaction can update or delete the rows until the repeatable reads transaction completes. However, repeatable-reads transactions do not provide phantom protection by performing range locking, as serializable transactions do. Other transactions can insert values that can be read by the repeatable-reads transaction and can update rows so that they match the search criteria of the repeatable-reads transaction. Note Transaction isolation level 2 is only supported for data-only-locked tables. If you use transaction isolation level 2 (repeatable reads) on allpageslocked tables, isolation level 3 (serializable reads) is also enforced. To enforce repeatable reads at a session level, use: set transaction isolation level 2 or set transaction isolation level repeatable readCHAPTER 19 Transactions: Maintaining Data Consistency and Recovery Transact-SQL User’s Guide 647 To enforce transaction isolation level 2 from a query, use: select title_id, price, advance from titles at isolation 2 or select title_id, price, advance from titles at isolation repeatable read Transaction isolation level 2 is supported only at the transaction level. You cannot use the at isolation clause in a select or readtext statement to set the isolation level of a query to 2. See “Changing the isolation level for a query” on page 647. For more information on transaction isolation levels, see the Performance and Tuning Guide. Finding the status of the current isolation level The global variable @@isolation contains the current isolation level of your Transact-SQL session. Querying @@isolation returns the value of the active level (0, 1, or 3). For example: select @@isolation -------- 1 (1 row affected) For more information about isolation levels and locking, see the Performance and Tuning Guide. Changing the isolation level for a query You can change the isolation level for a query by using the at isolation clause with the select or readtext statements. The at isolation clause supports isolation levels 0, 1, and 3. It does not support isolation level 2. The read uncommitted, read committed, and serializable options of at isolation represent isolation levels as listed below: at isolation option Isolation level read uncommited 0 read committed 1Selecting the transaction mode and isolation level 648 Adaptive Server Enterprise For example, the following two statements query the same table at isolation levels 0 and 3, respectively: select * from titles at isolation read uncommitted select * from titles at isolation serializable The at isolation clause is valid only for single select and readtext queries or in the declare cursor statement. Adaptive Server returns a syntax error if you use at isolation: • With a query using the into clause • Within a subquery • With a query in the create view statement • With a query in the insert statement • With a query using the for browse clause If there is a union operator in the query, you must specify the at isolation clause after the last select. The SQL-92 standard defines read uncommitted, read committed, and serializable as options for at isolation and set transaction isolation level. A Transact-SQL extension also allows you to specify 0, 1, or 3, but not 2, for at isolation. To simplify the discussion of isolation levels, the at isolation examples in this manual do not use this extension. You can also enforce isolation level 3 using the holdlock keyword of the select statement. However, you cannot specify noholdlock or shared in a query that also specifies at isolation read uncommitted. (If you specify holdlock and isolation level 0 in a query, Adaptive Server issues a warning and ignores the at isolation clause.) When you use different ways to set an isolation level, the holdlock keyword takes precedence over the at isolation clause (except for isolation level 0), and at isolation takes precedence over the session level defined by set transaction isolation level. For more information about isolation levels and locking, see the Performance and Tuning Guide. serializable 3 at isolation option Isolation levelCHAPTER 19 Transactions: Maintaining Data Consistency and Recovery Transact-SQL User’s Guide 649 Isolation level precedences The following describes the precedence rules as they apply to the different methods of defining isolation levels: 1 The holdlock, noholdlock, and shared keywords take precedence over the at isolation clause and set transaction isolation level option, except in the case of isolation level 0. For example: /* This query executes at isolation level 3 */ select * from titles holdlock at isolation read committed create view authors_nolock as select * from authors noholdlock set transaction isolation level 3 /* This query executes at isolation level 1 */ select * from authors_nolock 2 The at isolation clause takes precedence over the set transaction isolation level option. For example: set transaction isolation level 2 /* executes at isolation level 0 */ select * from publishers at isolation read uncommitted You cannot use the read uncommitted option of at isolation in the same query as the holdlock, noholdlock, and shared keywords. 3 The transaction isolation level 0 option of the set command takes precedence over the holdlock, noholdlock, and shared keywords. For example: set transaction isolation level 0 /* executes at isolation level 0 */ select * from titles holdlock Adaptive Server issues a warning before executing the above query. Cursors and isolation levels Adaptive Server provides three isolation levels for cursors:Selecting the transaction mode and isolation level 650 Adaptive Server Enterprise • Level 0 – Adaptive Server uses no locks on base table pages that contain a row representing a current cursor position. Cursors acquire no read locks for their scans, so they do not block other applications from accessing the same data. However, cursors operating at this isolation level are not updatable, and they require a unique index on the base table to ensure the accuracy of their scans. • Level 1 – Adaptive Server uses a shared or update lock on base table pages that contain a row representing a current cursor position. The page remains locked until the current cursor position moves off the page (as a result of fetch statements), or the cursor is closed. If an index is used to search the base table rows, it also applies shared or update locks to the corresponding index pages. This is the default locking behavior for Adaptive Server. • Level 3 – Adaptive Server uses a shared or update lock on any base table pages that have been read in a transaction on behalf of the cursor. In addition, the locks are held until the transaction ends, as opposed to being released when the data page is no longer needed. The holdlock keyword applies this locking level to the base tables, as specified by the query on the tables or views. Isolation level 2 is not supported for cursors. Besides using holdlock for isolation level 3, you can use set transaction isolation level to specify any of the four isolation levels for your session. When you use set transaction isolation level, any cursor you open uses the specified isolation level, unless the transaction isolation level is set at 2. In this case, the cursor uses isolation level 3. You can also use the select statement’s at isolation clause to specify isolation level 0, 1, or 3 for a specific cursor. For example: declare commit_crsr cursor for select * from titles at isolation read committed This statement makes the cursor operate at isolation level 1, regardless of the isolation level of the transaction or session. If you declare a cursor at isolation level 0 (read uncommitted), Adaptive Server also defines the cursor as readonly. You cannot specify the for update clause along with at isolation read uncommitted in a declare cursor statement. Adaptive Server determines a cursor’s isolation level when you open the cursor (not when you declare it), based on the following: • If the cursor was declared with the at isolation clause, that isolation level overrides the transaction isolation level in which it is opened.CHAPTER 19 Transactions: Maintaining Data Consistency and Recovery Transact-SQL User’s Guide 651 • If the cursor was not declared with at isolation, the cursor uses the isolation level in which it is opened. If you close the cursor and reopen it later, the cursor acquires the current isolation level of the transaction. Adaptive Server compiles the cursor’s query when you declare it. This compilation process is different for isolation level 0 as compared to isolation levels 1 or 3. If you declare a language or client cursor in a transaction with isolation level 1 or 3, opening it in a transaction at isolation level 0 causes an error. For example: set transaction isolation level 1 declare publishers_crsr cursor for select * from publishers open publishers_crsr /* no error */ fetch publishers_crsr close publishers_crsr set transaction isolation level 0 open publishers_crsr /* error */ Stored procedures and isolation levels The Sybase system procedures always operate at isolation level 1, regardless of the isolation level of the transaction or session. User stored procedures operate at the isolation level of the transaction that executes it. If the isolation level changes within a stored procedure, the new isolation level remains in effect only during the execution of the stored procedure. Triggers and isolation levels Since triggers are fired by data modification statements (like insert), all triggers execute at either the transaction’s isolation level or isolation level 1, whichever is higher. So, if a trigger fires in a transaction at level 0, Adaptive Server sets the trigger’s isolation level to 1 before executing its first statement.Selecting the transaction mode and isolation level 652 Adaptive Server Enterprise Compliance with SQL standards To get transactions that comply with SQL standards, you must set the chained and transaction isolation level 3 options at the beginning of every application that changes the mode and isolation level for subsequent transactions. If your application uses cursors, you must also set the close on endtran option. These options are described in Using cursors in transactions on page 662. Using the lock table command to improve performance The lock table command allows you to explicitly request that before a table is accessed, a table lock be put on it for the duration of a transaction. This is use useful when an immediate table lock may reduce the overhead of acquiring a large number of row or page locks and save overall locking time. Examples of such cases are: • A table will be scanned more than once in the same transaction, and each scan may need to acquire many page or row locks. • A scan will exceed a table’s lock-promotion threshold and will therefore attempt to escalate to a table lock in any event. If a table lock is not explicitly requested, a scan acquires page or row locks until it reaches the table’s lock promotion threshold (see system procedure sp_setpglockpromote), at which point it tries to acquire a table lock. Syntax of the lock table command The syntax of lock table is: lock table table_name in {share | exclusive} mode [wait [no_of_seconds] | nowait] The wait/nowait option allows you to specify how long the command waits to acquire a table lock if it is blocked (see “Using the wait/nowait options of the lock table command” on page 653). The following considerations apply to the use of lock table: • lock table can be issued only within a transaction. • You cannot use lock table on system tables. • You can first use lock table to lock a table in share mode, then use it to upgrade the lock to exclusive mode.CHAPTER 19 Transactions: Maintaining Data Consistency and Recovery Transact-SQL User’s Guide 653 • You can use separate lock table commands to lock multiple tables within the same transaction. • Once a table lock is obtained, there is no difference between a table locked with lock table and a table locked through lock promotion without the lock table command. Using the wait/nowait options of the lock table command Use the wait option in the lock table command to specify the length of time the command waits to acquire a table lock. For example, the following command, inside a transaction, sets a wait period of 2 seconds for acquiring a table lock on the titles table: lock table titles in share mode wait 2 If the wait time expires before a table lock is acquired, the transaction proceeds, and row or page locking is used, exactly as it would have been without the lock table command. The following informational message (error number 12207) is generated: Could not acquire a lock within the specified wait period. COMMAND level wait... For an example of error handling during transactions, see lock table in the Reference Manual. Note If you use lock table...wait without specifying no_of_seconds, the command waits indefinitely for a lock. You can set time limits on waiting for a lock at the session level and the system level. The wait period set with the lock table command overrides both of these, as described in the following section. The nowait option is equivalent to the wait option with a 0-second wait: lock table either obtains a table lock immediately or generates the informational message given above. If the lock is not acquired, the transaction proceeds as it would have without lock table.Using transactions in stored procedures and triggers 654 Adaptive Server Enterprise Using transactions in stored procedures and triggers You can use transactions in stored procedures and triggers just as with statement batches. If a transaction in a batch or stored procedure invokes another stored procedure or trigger containing a transaction, that second transaction is nested into the first one. The first explicit or implicit (using chained mode) begin transaction starts the transaction in the batch, stored procedure, or trigger. Each subsequent begin transaction increments the nesting level. Each subsequent commit transaction decrements the nesting level until it reaches 0. Adaptive Server then commits the entire transaction. A rollback transaction aborts the entire transaction up to the first begin transaction regardless of the nesting level or the number of stored procedures and triggers it spans. In stored procedures and triggers, the number of begin transaction statements must match the number of commit transaction statements. This also applies to stored procedures that use chained mode. The first statement that implicitly begins a transaction must also have a matching commit transaction. Figure 19-1 demonstrates how nested transaction statements work within stored procedures:CHAPTER 19 Transactions: Maintaining Data Consistency and Recovery Transact-SQL User’s Guide 655 Figure 19-1: Nesting transaction statements rollback transaction statements in stored procedures do not affect subsequent statements in the procedure or batch that originally called the procedure. Adaptive Server executes subsequent statements in the stored procedure or batch. However, rollback transaction statements in triggers abort the batch so that subsequent statements are not executed. Note rollback statements in triggers: 1) roll back the transaction, 2) complete subsequent statements in the trigger, and 3) abort the batch so that subsequent statements in the batch are not executed. Using transactions in stored procedures and triggers 656 Adaptive Server Enterprise For example, the following batch calls the stored procedure myproc, which includes a rollback transaction statement: begin tran update titles set ... insert into titles ... execute myproc delete titles where ... The update and insert statements are rolled back and the transaction is aborted. Adaptive Server continues the batch and executes the delete statement. However, if there is an insert trigger on a table that includes a rollback transaction, the entire batch is aborted and the delete is not executed. For example: begin tran update authors set ... insert into authors ... delete authors where ... Different transaction modes or isolation levels for stored procedures have certain requirements, which are described under “Transaction modes and stored procedures” on page 660. Triggers are not affected by the current transaction mode, since they are called as part of a data modification statement. Errors and transaction rollbacks Errors that affect data integrity can affect the state of implicit or explicit transactions: • Errors with severity levels of 19 or greater Since these errors terminate the user connection to the server, any errors of level 19 or greater that occur while a user transaction is in progress abort the transaction and roll back all statements to the outermost begin transaction. Adaptive Server always rolls back any uncommitted transactions at the end of a session. • Errors in data modification commands that affect data integrity (see Table 19-5): • Arithmetic overflow and divide-by-zero errors (effects on transactions can be changed with the set arithabort arith_overflow command) • Permissions violationsCHAPTER 19 Transactions: Maintaining Data Consistency and Recovery Transact-SQL User’s Guide 657 • Rules violations • Duplicate key violations Table 19-4 summarizes how rollback affects Adaptive Server processing in several different contexts (such as within a transaction, stored procedure, or trigger):Using transactions in stored procedures and triggers 658 Adaptive Server Enterprise Table 19-4: How rollback affects processing In stored procedures and triggers, the number of begin transaction statements must match the number of commit statements. A procedure or trigger that contains unpaired begin/commit statements produces a warning message when it is executed. This also applies to stored procedures that use chained mode: the first statement that implicitly begins a transaction must have a matching Context Effects of rollback Transaction only All data modifications since the start of the transaction are rolled back. If a transaction spans multiple batches, rollback affects all of those batches. Any commands issued after the rollback are executed. Stored procedure only None. Stored procedure in a transaction All data modifications since the start of the transaction are rolled back. If a transaction spans multiple batches, rollback affects all those batches. Any commands issued after the rollback are executed. Stored procedure produces error message 266: “Transaction count after EXECUTE indicates that a COMMIT or ROLLBACK TRAN is missing.” Trigger only Trigger completes, but trigger effects are rolled back. Any remaining commands in the batch are not executed. Processing resumes at the next batch. Trigger in a transaction Trigger completes, but trigger effects are rolled back. All data modifications since the start of the transaction are rolled back. If a transaction spans multiple batches, rollback affects all those batches. Any remaining commands in the batch are not executed. Processing resumes at the next batch. Nested trigger Inner trigger completes, but all trigger effects are rolled back. Any remaining commands in the batch are not executed. Processing resumes at the next batch. Nested trigger in a transaction Inner trigger completes, but all trigger effects are rolled back. All data modifications since the start of the transaction are rolled back. If a transaction spans multiple batches, rollback affects all those batches. Any remaining commands in the batch are not executed. Processing resumes at the next batch.CHAPTER 19 Transactions: Maintaining Data Consistency and Recovery Transact-SQL User’s Guide 659 commit. With duplicate key errors and rules violations, the trigger completes (unless there is also a return statement), and statements such as print, raiserror, or remote procedure calls are performed. Then, the trigger and the rest of the transaction are rolled back, and the rest of the batch is aborted. Remote procedure calls executed from inside a normal SQL transaction (not using the DB-Library two-phase commit) are not rolled back by a rollback statement. Table 19-5 summarizes how a rollback caused by a duplicate key error or a rules violation affects Adaptive Server processing in several different contexts: Table 19-5: Rollbacks caused by errors in data modification Context Effects of data modification errors during transactions Transaction only Current command is aborted. Previous commands are not rolled back, and subsequent commands are executed. Transaction within a stored procedure Same as above. Stored procedure in a transaction Same as above. Stored procedure in a transaction Same as above. Trigger only Trigger completes, but trigger effects are rolled back. Any remaining commands in the batch are not executed. Processing resumes at the next batch. Trigger in a transaction Trigger completes, but trigger effects are rolled back. All data modifications since the start of the transaction are rolled back. If a transaction spans multiple batches, the rollback affects all of those batches. Any remaining commands in the batch are not executed. Processing resumes at the next batch. Nested trigger Inner trigger completes, but all trigger effects are rolled back. Any remaining commands in the batch are not executed. Processing resumes at the next batch. Nested trigger in a transaction Inner trigger completes, but all trigger effects are rolled back. All data modifications since the start of the transaction are rolled back. If a transaction spans multiple batches, the rollback affects all of those batches. Any remaining commands in the batch are not executed. Processing resumes at the next batch.Using transactions in stored procedures and triggers 660 Adaptive Server Enterprise Transaction modes and stored procedures Stored procedures written to use the unchained transaction mode may be incompatible with other transactions using chained mode, and vice versa. For example, here is a valid stored procedure using chained transaction mode: create proc myproc as insert into publishers values ("9996", null, null, null) commit work A program using unchained transaction mode would fail if it called this procedure because the commit does not have a corresponding begin. You may encounter other problems: • Applications that start a transaction using chained mode may create impossibly long transactions or may hold data locks for the entire length of their session, degrading Adaptive Server’s performance. • Applications may nest transactions at unexpected times. This can produce different results, depending on the transaction mode. As a rule, applications using one transaction mode should call stored procedures written to use that mode. The exceptions to that rule are Sybase system procedures (except for sp_procxmode) that can be invoked by sessions using any transaction mode. (For information about sp_proxmode, see “Setting transaction modes for stored procedures” on page 661.) If no transaction is active when you execute a system procedure, Adaptive Server turns off chained mode for the duration of the procedure. Before returning, it resets the mode its original setting. Trigger with rollback followed by an error in the transaction Trigger effects are rolled back. All data modifications since the start of the transaction are rolled back. If a transaction spans multiple batches, the rollback affects all of those batches. Trigger continues and gets duplicate key or rules error. Normally, the trigger rolls back effects and continues, but trigger effects are not rolled back in this case. After the trigger completes, any remaining commands in the batch are not executed. Processing resumes at the next batch. Stored procedure in a transaction Same as above. Context Effects of data modification errors during transactionsCHAPTER 19 Transactions: Maintaining Data Consistency and Recovery Transact-SQL User’s Guide 661 Adaptive Server tags all procedures with the transaction mode (“chained” or “unchained”) of the session in which they are created. This helps avoid problems associated with transactions that use one mode to invoke transactions that use the other mode. A stored procedure tagged as “chained” is not executable in sessions using unchained transaction mode, and vice versa. Triggers are executable in any transaction mode. Since they are always called as part of a data modification statement, either they are part of a chained transaction (if the session uses chained mode) or they maintain their current transaction mode. Warning! When using transaction modes, be aware of the effects each setting can have on your applications. Setting transaction modes for stored procedures Use sp_procxmode to display or change the transaction mode of stored procedures. For example, to change the transaction mode for the stored procedure byroyalty to “chained,” enter: sp_procxmode byroyalty, "chained" sp_procxmode “anymode” lets stored procedures run under either chained or unchained transaction mode. For example: sp_procxmode byroyalty, "anymode" Use sp_procxmode without any parameter values to get the transaction modes for all stored procedures in the current database: sp_procxmode procedure name transaction mode ------------------------- -------------------- byroyalty Any Mode discount_proc Unchained history_proc Unchained insert_sales_proc Unchained insert_salesdetail_proc Unchained storeid_proc Unchained storename_proc Unchained title_proc Unchained titleid_proc Unchained (9 rows affected, return status = 0) You can use sp_procxmode only in unchained transaction mode.Using cursors in transactions 662 Adaptive Server Enterprise To change a procedure’s transaction mode, you must be a System Administrator, the Database Owner, or the owner of the procedure. Using cursors in transactions By default, Adaptive Server does not change a cursor’s state (open or closed) when a transaction ends through a commit or rollback. The SQL standards, however, associate an open cursor with its active transaction. Committing or rolling back that transaction automatically closes any open cursors associated with it. To enforce this SQL standards-compliant behavior, Adaptive Server provides the close on endtran option of the set command. In addition, if you set chained mode to on, Adaptive Server starts a transaction when you open a cursor and closes that cursor when the outermost transaction is committed or rolled back. For example, by default, this sequence of statements produces an error: open test_crsr commit tran open test_crsr If you set either the close on endtran or chained options to on, the cursor’s state changes from open to closed after the outermost transaction is committed. This allows the cursor to be reopened. Note Since client application buffer rows are returned through cursors, and allow users to scroll within those buffers, those client applications should not scroll backward after a transaction aborts. The rows in a client cache may become invalid because of a transaction rollback (unknown to the client) that is enforced by the close on endtran option or the chained mode. Any exclusive locks acquired by a cursor in a transaction are held until the end of that transaction. This also applies to shared locks when you use the holdlock keyword, the at isolation serializable clause, or the set isolation level 3 option. However, if you do not set the close on endtran option, the cursor remains open past the end of the transaction, and its current page lock remains in effect. It may also continue to acquire locks as it fetches additional rows. The following rules define the behavior of updates through a cursor with regard to transactions:CHAPTER 19 Transactions: Maintaining Data Consistency and Recovery Transact-SQL User’s Guide 663 • If an update occurs within an explicit transaction, the update is considered part of the transaction. If the transaction commits, any updates included with the transaction also commit. If the transaction aborts, any updates included with the transaction are rolled back. Updates through the same cursor that occurred outside the aborted transaction are not affected. • If updates through a cursor occur within an explicit (and client-specified) transaction, Adaptive Server does not commit them when the cursor is closed. It commits or rolls back pending updates only when the transaction associated with that cursor ends. • A transaction commit or abort has no effect on SQL cursor statements that do not manipulate result rows, such as declare cursor, open cursor, close cursor, set cursor rows, and deallocate cursor. For example, if the client opens a cursor within a transaction, and the transaction aborts, the cursor remains open after the abort (unless the close on endtran is set or the chained mode is used). Issues to consider when using transactions You should consider the following issues when using transactions in your applications: • A rollback statement, without a transaction or savepoint name, always rolls back statements to the outermost begin transaction (explicit or implicit) statement and cancels the transaction. If there is no current transaction when you issue rollback, the statement has no effect. In triggers or stored procedures, rollback statements, without transaction or savepoint names, roll back all statements to the outermost begin transaction (explicit or implicit). • rollback does not produce any messages to the user. If warnings are needed, use raiserror or print statements. • Grouping a large number of Transact-SQL commands into one longrunning transaction may affect recovery time. If Adaptive Server fails during a long transaction, recovery time increases, since Adaptive Server must first undo the entire transaction. • You can have as many databases in a user transaction as there are in your Adaptive Server installation. For example, if your Adaptive Server has 25 databases, you can include 25 databases in your user transactions.Backup and recovery of transactions 664 Adaptive Server Enterprise • A remote procedure call (RPC) can be executed independently from any transaction in which it is included. In a standard transaction (one that does not use Open Client DB-Library/C two-phase commit or Adaptive Server Distributed Transaction Management features), commands executed via an RPC by a remote server are not rolled back with rollback and do not depend on commit to be executed. • Transactions cannot span more than one connection between a client application and a server. For example, a DB-Library/C application cannot group SQL statements in a transaction across multiple open DBPROCESS connections. Backup and recovery of transactions Every change to a database, whether it is the result of a single update statement or a grouped set of SQL statements, is recorded in the system table syslogs. This table is called the transaction log. Some commands that change the database are not logged, such as truncate table, bulk copy into a table that has no indexes, select into, writetext, and dump transaction with no_log. The transaction log records update, insert, or delete statements on a momentto-moment basis. When a transaction begins, a begin transaction event is recorded in the log. As each data modification statement is received, it is recorded in the log. The change is always recorded in the log before any change is made in the database itself. This type of log, called a write-ahead log, ensures that the database can be recovered completely in case of a failure. Failures can be due to hardware or media problems, system software problems, application software problems, program-directed cancellations of transactions, or a user decision to cancel the transaction. In case of any of these failures, the transaction log can be played back against a copy of the database restored from a backup made with the dump commands. To recover from a failure, transactions that were in progress but not yet committed at the time of the failure must be undone, because a partial transaction is not an accurate change. Completed transactions must be redone if there is no guarantee that they have been written to the database device.CHAPTER 19 Transactions: Maintaining Data Consistency and Recovery Transact-SQL User’s Guide 665 If there are active, long-running transactions that are not committed when Adaptive Server fails, undoing the changes may require as much time as the transactions have been running. Such cases include transactions that do not contain a commit transaction or rollback transaction to match a begin transaction. This prevents Adaptive Server from writing any changes and increases recovery time. Adaptive Server’s dynamic dump allows the database and transaction log to be backed up while use of the database continues. Make frequent backups of your database transaction log. The more often you back up your data, the less work will be lost if a system failure occurs. The owner of each database or a user with the ss_oper role is responsible for backing up the database and its transaction log with the dump commands, though permission to execute them can be transferred to other users. Permission to use the load commands, however, defaults to the Database Owner and cannot be transferred. Once the appropriate load commands are issued, Adaptive Server handles all aspects of the recovery process. Adaptive Server also controls the checkpoint interval, which is the point at which all data pages that have been changed are guaranteed to have been written to the database device. Users can force a checkpoint, if necessary, with the checkpoint command. For more information about backup and recovery, see the Reference Manual and the System Administration Guide.Backup and recovery of transactions 666 Adaptive Server EnterpriseTransact-SQL User’s Guide 667 C H A P T E R 2 0 Locking Commands and Options Adaptive Server provides a wide range of commands and options for providing locking. This chapter reviews the types of locking available and how they are invoked through Transact SQL. This chapter includes the following sections: Setting a time limit on waiting for locks Adaptive Server allows you to specify a lock wait period that determines how long a command will wait to acquire locks: • You can specify a time limit on waiting to obtain a table lock with the wait/nowait option of the lock table command. • During a session, you can use the set lock command to specify a lock wait period for all subsequent commands issued during the session. • The sp_configure parameter lock wait period, used with the sessionlevel setting set lock wait nnn, is only applicable to user-defined tables. These settings have no influence on system tables. • Within a stored procedure, you can use the set lock command to specify a lock wait period for all subsequent commands issued within the stored procedure. • You can use the lock wait period option of sp_configure to set a Serverwide lock wait period. Topic Page Setting a time limit on waiting for locks 667 Readpast locking for queue processing 671Setting a time limit on waiting for locks 668 Adaptive Server Enterprise wait/nowait option of the lock table command Within a transaction, the lock table command allows you to request a table lock on a table without waiting for the command to acquire enough row-level or page-level locks to escalate to a table lock. The lock table command contains a wait/nowait option that allows you to specify the length of time the command will wait until operations in other transactions relinquish any locks they have on the target table. The syntax for lock table is: lock table table_name in {share | exclusive} mode [wait [no_of_seconds] | nowait] The following command, inside a transaction, sets a wait period of 2 seconds for acquiring a table lock on the titles table: lock table titles in share mode wait 2 If the wait time expires before a table lock is acquired, the transaction proceeds, and row or page locking is used, exactly as it would have been without lock table, and the following informational message (error number 12207) is generated: Could not acquire a lock within the specified wait period. COMMAND level wait... For a code example of handling this error message during a transaction, see lock table in the Reference Manual. Note If you use lock table...wait without specifying no_of_seconds, the command waits indefinitely for a lock. You can set time limits on waiting for a lock at the session level and the system level, as described in the following sections. The wait period set with the lock table command overrides both of these The nowait option is equivalent to the wait option with a 0-second wait: lock table either obtains a table lock immediately or generates the informational message given above. If the lock is not acquired, the transaction proceeds as it would have without the lock table command. You can use the set lock command at either the session level or within a stored procedure to control the length of time a task will wait to acquire locks. A System Administrator can use the sp_configure option, lock wait period, to set a server-wide time limit on acquiring locks.CHAPTER 20 Locking Commands and Options Transact-SQL User’s Guide 669 Setting a session-level lock-wait limit You can use set lock wait to control the length of time that a command in a session or in a stored procedure waits to acquire locks. The syntax is: set lock {wait no_of_seconds | nowait} no_of_seconds is an integer. Thus, the following example sets a session-level time limit of 5 seconds on waiting for locks: set lock wait 5 With one exception, if the set lock wait period expires before a command acquires a lock, the command fails, the transaction containing it is rolled back, and the following error message is generated: Msg 12205, Level 17, State 2: Server ’sagan’, Line 1: Could not acquire a lock within the specified wait period. SESSION level wait period=300 seconds, spid=12, lock type=shared page, dbid=9, objid=2080010441, pageno=92300, rowno=0. Aborting the transaction. The exception to this occurs when lock table in a transaction sets a longer wait period than set lock wait. In this case, the transaction uses the lock table wait period before timing out, as described in the preceding section. The set lock nowait option is equivalent to the set lock wait option with a 0- second wait. If a command other than lock table cannot obtain a requested lock immediately, the command fails, its transaction is rolled back, and the preceding error message is generated. If both a server-wide lock-wait limit and a session-level lock-wait limit are set, the session-level limit takes precedence. If no session-level wait period is set with set lock wait, the server-level wait period is used. Note Stored procedures do not use a wait period set at either the server level or the session level. The wait period for commands in a stored procedure is unbounded, unless you explicitly specify a time limit by using the set lock wait command inside the stored procedure. Setting a server-wide lock-wait limit A System Administrator can configure a server-wide lock-wait limit with the configuration parameter lock wait period. The syntax is: Setting a time limit on waiting for locks 670 Adaptive Server Enterprise sp_configure "lock wait period" [, no_of_seconds] If the lock-wait period expires before a command acquires a lock, unless there is an overriding set lock wait or lock table wait period, the command fails, the transaction containing it is rolled back, and the following error message is generated: Msg 12205, Level 17, State 2: Server ’wiz’, Line 1: Could not acquire a lock within the specified wait period. SERVER level wait period=300 seconds, spid=12, lock type=shared page, dbid=9, objid=2080010441, pageno=92300, rowno=0. Aborting the transaction. A time limit entered through set lock wait or lock table wait overrides a serverlevel lock-wait period. Thus, for example, if the server-level wait period is 5 seconds and the session-level wait period is 10 seconds, an update command waits 10 seconds to acquire a lock before failing and aborting its transaction. The default server-level lock-wait period is effectively “wait forever.” To restore the default after setting a time-limited wait, you can use sp_configure to set the value of lock wait period as follows: sp_configure "lock wait period", 0, "default" Information on the number of lock-wait timeouts sp_sysmon reports on the number of times tasks waiting for locks did not acquire the lock within the specified period. See the Performance and Tuning Guide for more information.CHAPTER 20 Locking Commands and Options Transact-SQL User’s Guide 671 Readpast locking for queue processing Readpast locking is an option available for the select and readtext commands and the data modification commands update, delete, and writetext. It instructs a command to silently skip all incompatible locks it encounters, without blocking, terminating, or generating a message. It is primarily used when the rows of a table constitute a queue. In such a case, a number of tasks may access the table to process the queued rows, which could, for example, represent queued customers or customer orders. A given task is not concerned with processing a specific member of the queue, but with processing any available members of the queue that meet its selection criteria. Readpast syntax The syntax for using readpast locking is: {select | update | delete} ... from tablename [holdlock | noholdlock] [readpast] [shared] ... readtext [[database.]owner.]table_name.column_name text_pointer offset size [holdlock | noholdlock] [shared] [readpast] ... writetext [[database.]owner.]table_name.column_name text_pointer [readpast] [with log] data Incompatible locks during readpast queries For select and readtext commands, incompatible locks are exclusive locks. Therefore, select and readpast commands can access any rows or pages on which shared or update locks are held. For delete, update, and writetext commands, any type of page or row lock is incompatible, so that: • All rows with shared, update, or exclusive row locks are skipped in datarows-locked tables, and • All pages with shared, update, or exclusive locks are skipped in datapageslocked tables.Readpast locking for queue processing 672 Adaptive Server Enterprise All commands specifying readpast block if there is an exclusive table lock, except select commands executed at transaction isolation level 0. Allpages-locked tables and readpast queries If the readpast option is specified for an allpages-locked table, the readpast option is ignored. The command operates at the isolation level specified for the command or session: • If the isolation level is 0, dirty reads are performed, and the command returns values from locked rows, and does not block. • If the isolation level is 1 or 3, the command blocks when pages with incompatible locks must be read. Effects of isolation levels select queries with readpast Readpast locking is designed to be used at transaction isolation level 1 or 2. Session-level transaction isolation levels and readpast For data-only-locked tables, the effects of readpast on a table in a select command are shown in Table 20-1. CHAPTER 20 Locking Commands and Options Transact-SQL User’s Guide 673 Table 20-1: Session-level isolation level and the use of readpast Query-level isolation levels and readpast If select commands that specify readpast also include any of the following clauses, the commands fail and display error messages: • The at isolation clause, specifying 0 or read uncommitted • The at isolation clause, specifying 3 or serializable • The holdlock keyword on the same table If a select query that specifies readpast also specifies at isolation 2 or at isolation repeatable read, shared locks are held on the readpast table or tables until the statement or transaction completes. readtext commands that include readpast and that specify at isolation read uncommitted automatically run at isolation level 0 after issuing a warning message. Data modification commands with readpast and isolation levels If the transaction isolation level for a session is 0, the delete, update, and writetext commands that use readpast do not issue warning messages. • For datapages-locked tables, these commands modify all rows on all pages that are not locked with incompatible locks. • For datarows-locked tables, they affect all rows that are not locked with incompatible locks. Session Isolation Level Effects 0, read uncommitted (dirty reads) readpast is ignored, and rows containing uncommitted transactions are returned to the user. A warning message is printed. 1, read committed Rows or pages with incompatible locks are skipped; no locks are held on the rows or pages read. 2, repeatable read Rows or pages with incompatible locks skipped; shared locks are held on all rows or pages that are read until the end of the statement or transaction. 3, serializable readpast is ignored, and the command executes at level 3. The command blocks on any rows or pages with incompatible locks.Readpast locking for queue processing 674 Adaptive Server Enterprise If the transaction isolation level for a session is 3 (serializable reads), the delete, update, and writetext commands that use readpast automatically block when they encounter a row or page with an incompatible lock. At transaction isolation level 2 (serializable reads), the delete, update, and writetext commands: • Modify all rows on all pages that are not locked with incompatible locks. • For datarows-locked tables, they affect all rows that are not locked with incompatible locks. text and image columns and readpast If a select command with the readpast option encounters a text column that has an incompatible lock on it, readpast locking retrieves the row, but returns the text column with a value of null. No distinction is made, in this case, between a text column containing a null value and a null value returned because the column is locked. If an update command with the readpast option applies to two or more text columns, and the first text column checked has an incompatible lock on it, readpast locking skips the row. If the column does not have an incompatible lock, the command acquires a lock and modifies the column. Then, if any subsequent text column in the row has an incompatible lock on it, the command blocks until it can obtain a lock and modify the column. A delete command with the readpast option skips the row if any of the text columns in the row have an incompatible lock. Readpast-locking examples The following examples illustrate readpast locking. To skip all rows that have exclusive locks on them: select * from titles readpast To update only rows that are not locked by another session: update titles set price = price * 1.1 from titles readpastCHAPTER 20 Locking Commands and Options Transact-SQL User’s Guide 675 To use readpast locking on the titles table but not on the authors or titleauthor table: select * from titles readpast, authors, titleauthor where titles.title_id = titleauthor.title_id and authors.au_id = titleauthor.au_id To delete only rows that are not locked in the stores table, but to allow the scan to block on the authors table: delete stores from stores readpast, authors where stores.city = authors.cityReadpast locking for queue processing 676 Adaptive Server EnterpriseTransact-SQL User’s Guide 677 A P P E N D I X A The pubs2 Database This appendix describes the sample database pubs2. This database contains the tables publishers, authors, titles, titleauthor, au_pix, salesdetail, sales, stores, discounts, roysched, and blurbs. The pubs2 database also contains primary and foreign keys, rules, defaults, views, triggers, and stored procedures. A diagram of the pubs2 database appears in Figure A-2 on page 705. For information about installing pubs2, see the Configuring Adaptive Server Enterprise for your platform. Tables in the pubs2 database The following sections describe each pubs2 table. In the tables, each column header specifies the column name, its datatype (including any user-defined datatypes), and its null or not null status. The column header also specifies any defaults, rules, triggers, and indexes that affect the column. publishers table publishers is defined as follows: create table publishers (pub_id char(4) not null, pub_name varchar(40) not null, city varchar(20) null, state char(2) null) Its primary key is pub_id: sp_primarykey publishers, pub_id Its pub_idrule rule is defined as:Tables in the pubs2 database 678 Adaptive Server Enterprise create rule pub_idrule as @pub_id in ("1389", "0736", "0877", "1622", "1756") or @pub_id like "99[0-9][0-9]" Table A-1 lists the contents of publishers: Table A-1: publishers table authors table authors is defined as follows: create table authors (au_id id not null, au_lname varchar(40) not null, au_fname varchar(20) not null, phone char(12) not null, address varchar(40) null, city varchar(20) null, state char(2) null, country varchar(12) null, postalcode char(10) null) Its primary key is au_id: sp_primarykey authors, au_id Its nonclustered index for the au_lname and au_fname columns is defined as: create nonclustered index aunmind on authors (au_lname, au_fname) The phone column has the following default: create default phonedflt as "UNKNOWN" sp_bindefault phonedft, "authors.phone" The following view uses authors: create view titleview as select title, au_ord, au_lname, price, total_sales, pub_id pub_id pub_name city state 0736 New Age Books Boston MA 0877 Binnet & Hardley Washington DC 1389 Algodata Infosystems Berkeley CAAPPENDIX A The pubs2 Database Transact-SQL User’s Guide 679 from authors, titles, titleauthor where authors.au_id = titleauthor.au_id and titles.title_id = titleauthor.title_id Table A-2 lists the contents of authors: Table A-2: authors table au_id au_- lname au_ fname phone address city state country postalcode 172-32- 1176 White Johnson 408 496- 7223 10932 Bigge Rd. Menlo Park CA USA 94025 213-46- 8915 Green Marjorie 510 986- 7020 309 63rd St. #411 Oakland CA USA 94618 238-95- 7766 Carson Cheryl 510 548- 7723 589 Darwin Ln. Berkeley CA USA 94705 267-41- 2394 O’Leary Michael 408 286- 2428 22 Cleveland Av. #14 San Jose CA USA 95128 274-80- 9391 Straight Dick 510 834- 2919 5420 College Av. Oakland CA USA 94609 341-22- 1782 Smith Meander 913 843- 0462 10 Mississippi Dr. Lawrence KS USA 66044 409-56- 7008 Bennet Abraham 510 658- 9932 6223 Bateman St. Berkeley CA USA 94705 427-17- 2319 Dull Ann 415 836- 7128 3410 Blonde St. Palo Alto CA USA 94301 472-27- 2349 Gringlesby Burt 707 938- 6445 PO Box 792 Covelo CA USA 95428 486-29- 1786 Locksley Chastity 415 585- 4620 18 Broadway Av. San Francisco CA USA 94130 527-72- 3246 Greene Morningst ar 615 297- 2723 22 Graybar House Rd. Nashville TN USA 37215 648-92- 1872 BlotchetHalls Reginald 503 745- 6402 55 Hillsdale Bl. Corvallis OR USA 97330 672-71- 3249 Yokomoto Akiko 415 935- 4228 3 Silver Ct. Walnut Creek CA USA 94595 712-45- 1867 del Castillo Innes 615 996- 8275 2286 Cram Pl. #86 Ann Arbor MI USA 48105 722-51- 5454 DeFrance Michel 219 547- 9982 3 Balding Pl. Gary IN USA 46403 724-08- 9931 Stringer Dirk 510 843- 2991 5420 Telegraph Av. Oakland CA USA 94609 724-80- 9391 MacFeather Stearns 510 354- 7128 44 Upland Hts. Oakland CA USA 94612Tables in the pubs2 database 680 Adaptive Server Enterprise titles table titles is defined as follows: create table titles (title_id tid not null, title varchar(80) not null, type char(12) not null, pub_id char(4) null, price money null, advance money null, total_sales int null, notes varchar(200) null, pubdate datetime not null, contract bit not null) Its primary key is title_id: sp_primarykey titles, title_id Its pub_id column is a foreign key to the publishers table: sp_foreignkey titles, publishers, pub_id Its nonclustered index for the title column is defined as: create nonclustered index titleind on titles (title) Its title_idrule is defined as: create rule title_idrule 756-30- 7391 Karsen Livia 510 534- 9219 5720 McAuley St. Oakland CA USA 94609 807-91- 6654 Panteley Sylvia 301 946- 8853 1956 Arlington Pl. Rockville MD USA 20853 846-92- 7186 Hunter Sheryl 415 836- 7128 3410 Blonde St. Palo Alto CA USA 94301 893-72- 1158 McBadden Heather 707 448- 4982 301 Putnam Vacaville CA USA 95688 899-46- 2035 Ringer Anne 801 826- 0752 67 Seventh Av. Salt Lake City UT USA 84152 998-72- 3567 Ringer Albert 801 826- 0752 67 Seventh Av. Salt Lake City UT USA 84152 au_id au_- lname au_ fname phone address city state country postalcodeAPPENDIX A The pubs2 Database Transact-SQL User’s Guide 681 as @title_id like "BU[0-9][0-9][0-9][0-9]" or @title_id like "[MT]C[0-9][0-9][0-9][0-9]" or @title_id like "P[SC][0-9][0-9][0-9][0-9]" or @title_id like "[A-Z][A-Z]xxxx" or @title_id like "[A-Z][A-Z]yyyy" The type column has the following default: create default typedflt as "UNDECIDED" sp_bindefault typedflt, "titles.type" The pubdate column has this default: create default datedflt as getdate() sp_bindefault datedflt, "titles.pubdate" titles uses the following trigger: create trigger deltitle on titles for delete as if (select count(*) from deleted, salesdetail where salesdetail.title_id = deleted.title_id) >0 begin rollback transaction print "You can’t delete a title with sales." end The following view uses titles: create view titleview as select title, au_ord, au_lname, price, total_sales, pub_id from authors, titles, titleauthor where authors.au_id = titleauthor.au_id and titles.title_id = titleauthor.title_id Table A-3 lists the contents of titles:Tables in the pubs2 database 682 Adaptive Server Enterprise Table A-3: titles table title- _id title type pub- _id price advance total_- sales notes pubdate contract BU1032 The Busy Executive’s Database Guide business 1389 19.99 5000.00 4095 An overview of available database systems with emphasis on common business applications. Illustrated. Jun 12, 1986 1 BU1111 Cooking with Computers: Surreptitious Balance Sheets business 1389 11.95 5000.00 3876 Helpful hints on how to use your electronic resources to the best advantage. Jun 9, 1988 1 BU2075 You Can Combat Computer Stress! business 0736 2.99 10125.00 18722 The latest medical and psychological techniques for living with the electronic office. Easy-tounderstand explanations. Jun 30, 1985 1 BU7832 Straight Talk About Computers business 1389 19.99 5000.00 4095 Annotated analysis of what computers can do for you: a nohype guide for the critical user. Jun 22, 1987 1APPENDIX A The pubs2 Database Transact-SQL User’s Guide 683 MC2222 Silicon Valley Gastronomic Treats mod_- cook 0877 19.99 0.00 2032 Favorite recipes for quick, easy, and elegant meals; tried and tested by people who never have time to eat, let alone cook. Jun 9, 1989 1 MC3021 The Gourmet Microwave mod_- cook 0877 2.99 15000.00 22246 Traditional French gourmet recipes adapted for modern microwave cooking. Jun 18, 1985 1 PC1035 But Is It User Friendly? popular_ comp 1389 22.95 7000.00 8780 A survey of software for the naive user, focusing on the “friendliness” of each. Jun 30, 1986 1 MC3026 The Psychology of Computer Cooking UNDECIDED 0877 NULL NULL NULL NULL Jul 24, 1991 0 title- _id title type pub- _id price advance total_- sales notes pubdate contractTables in the pubs2 database 684 Adaptive Server Enterprise PC8888 Secrets of Silicon Valle y popular_ comp 1389 20.00 8000.00 4095 Muckraking reporting by two courageous women on the world’s largest computer hardware and software manufacturers. Jun 12, 1987 1 PC9999 Net Etiquette popular_ comp 1389 NULL NULL NULL A must-read for computer conferencing debutantes! Jul 24, 1996 0 PS1372 Computer Phobic and Non-Phobic Individuals: Behavior Var iatio n s psychology 0877 21.59 7000.00 375 A must for the specialist, this book examines the difference between those who hate and fear computers and those who think they are swell. Oct 21,1990 1 title- _id title type pub- _id price advance total_- sales notes pubdate contractAPPENDIX A The pubs2 Database Transact-SQL User’s Guide 685 PS2091 Is Anger the Enemy? psychology 0736 10.95 2275.00 2045 Carefully researched study of the effects of strong emotions on the body. Metabolic charts included. Jun 15, 1989 1 PS2106 Life Without Fear psychology 0736 7.00 6000.00 111 New exercise, meditation, and nutritional techniques that can reduce the shock of daily interactions. Popular audience. Sample menus included. Exercise video available separately. Oct 5, 1990 1 PS3333 Prolonged Data Deprivation: Four Case Studies psychology 0736 19.99 2000.00 4072 What happens when the data runs dry? Searching evaluations of information shortage effects on heavy users. Jun 12, 1988 1 title- _id title type pub- _id price advance total_- sales notes pubdate contractTables in the pubs2 database 686 Adaptive Server Enterprise PS7777 Emotional Security: A New Algorithm psychology 0736 7.99 4000.00 3336 Protecting yourself and your loved ones from undue emotional stress in the modern world. Use of computer and nutritional aids emphasized. Jun 12, 1988 1 TC3218 Onions, Leeks, and Garlic: Cooking Secrets of the Mediterranean trad_- cook 0877 20.95 7000.00 375 Profusely illustrated in color, this makes a wonderful gift book for a cuisineoriented friend. Oct 21, 1990 1 TC4203 Fifty Years in Buckingham Palace Kitchens trad_coo k 0877 11.95 4000.00 15096 More anecdotes from the Queen’s favorite cook, describing life among English royalty. Recipes, techniques, tender vignettes. Jun 12, 1985 1 title- _id title type pub- _id price advance total_- sales notes pubdate contractAPPENDIX A The pubs2 Database Transact-SQL User’s Guide 687 titleauthor table titleauthor is defined as follows: create table titleauthor (au_id id not null, title_id tid not null, au_ord tinyint null, royaltyper int null) Its primary keys are au_id and title_id: sp_primarykey titleauthor, au_id, title_id Its title_id and au_id columns are foreign keys to titles and authors: sp_foreignkey titleauthor, titles, title_id sp_foreignkey titleauthor, authors, au_id Its nonclustered index for the au_id column is defined as: create nonclustered index auidind TC7777 Sushi, Anyone? trad_coo k 0877 14.99 8000.00 4095 Detailed instructions on improving your position in life by learning how to make authentic Japanese sushi in your spare time. 5-10% increase in number of friends per recipe reported from beta test. Jun 12, 1987 1 title- _id title type pub- _id price advance total_- sales notes pubdate contractTables in the pubs2 database 688 Adaptive Server Enterprise on titleauthor(au_id) Its nonclustered index for the title_id column is defined as: create nonclustered index titleidind on titleauthor(title_id) The following view uses titleauthor: create view titleview as select title, au_ord, au_lname, price, total_sales, pub_id from authors, titles, titleauthor where authors.au_id = titleauthor.au_id and titles.title_id = titleauthor.title_id The following procedure uses titleauthor: create procedure byroyalty @percentage int as select au_id from titleauthor where titleauthor.royaltyper = @percentage Table A-4 lists the contents of titleauthor:APPENDIX A The pubs2 Database Transact-SQL User’s Guide 689 Table A-4: titleauthor table salesdetail table salesdetail is defined as follows: create table salesdetail (stor_id char(4) not null, ord_num numeric(6,0), title_id tid not null, qty smallint not null, discount float not null) au_id title_id au_ord royaltyper 172-32-1176 PS3333 1 100 213-46-8915 BU1032 2 40 213-46-8915 BU2075 1 100 238-95-7766 PC1035 1 100 267-41-2394 BU1111 2 40 267-41-2394 TC7777 2 30 274-80-9391 BU7832 1 100 409-56-7008 BU1032 1 60 427-17-2319 PC8888 1 50 472-27-2349 TC7777 3 30 486-29-1786 PC9999 1 100 486-29-1786 PS7777 1 100 648-92-1872 TC4203 1 100 672-71-3249 TC7777 1 40 712-45-1867 MC2222 1 100 722-51-5454 MC3021 1 75 724-80-9391 BU1111 1 60 724-80-9391 PS1372 2 25 756-30-7391 PS1372 1 75 807-91-6654 TC3218 1 100 846-92-7186 PC8888 2 50 899-46-2035 MC3021 2 25 899-46-2035 PS2091 2 50 998-72-3567 PS2091 1 50 998-72-3567 PS2106 1 100Tables in the pubs2 database 690 Adaptive Server Enterprise Its primary keys are stor_id and ord_num: sp_primarykey salesdetail, stor_id, ord_num Its title_id, stor_id, and ord_num columns are foreign keys to titles and sales: sp_foreignkey salesdetail, titles, title_id sp_foreignkey salesdetail, sales, stor_id, ord_num Its nonclustered index for the title_id column is defined as: create nonclustered index titleidind on salesdetail (title_id) Its nonclustered index for the stor_id column is defined as: create nonclustered index salesdetailind on salesdetail (stor_id) Its title_idrule rule is defined as: create rule title_idrule as @title_id like "BU[0-9][0-9][0-9][0-9]" or @title_id like "[MT]C[0-9][0-9][0-9][0-9]" or @title_id like "P[SC][0-9][0-9][0-9][0-9]" or @title_id like "[A-Z][A-Z]xxxx" or @title_id like "[A-Z][A-Z]yyyy" salesdetail uses the following trigger: create trigger totalsales_trig on salesdetail for insert, update, delete as /* Save processing: return if there are no rows affected */ if @@rowcount = 0 begin return end /* add all the new values */ /* use isnull: a null value in the titles table means ** "no sales yet" not "sales unknown" */ update titles set total_sales = isnull(total_sales, 0) + (select sum(qty) from inserted where titles.title_id = inserted.title_id) where title_id in (select title_id from inserted) /* remove all values being deleted or updated */APPENDIX A The pubs2 Database Transact-SQL User’s Guide 691 update titles set total_sales = isnull(total_sales, 0) - (select sum(qty) from deleted where titles.title_id = deleted.title_id) where title_id in (select title_id from deleted) Table A-5 lists the contents of salesdetail: Table A-5: salesdetail table stor_id ord_num title_id qty discount 7896 234518 TC3218 75 40.000000 7896 234518 TC7777 75 40.000000 7131 Asoap432 TC3218 50 40.000000 7131 Asoap432 TC7777 80 40.000000 5023 XS-135-DER-432-8J2 TC3218 85 40.000000 8042 91-A-7 PS3333 90 45.000000 8042 91-A-7 TC3218 40 45.000000 8042 91-A-7 PS2106 30 45.000000 8042 91-V-7 PS2106 50 45.000000 8042 55-V-7 PS2106 31 45.000000 8042 91-A-7 MC3021 69 45.000000 5023 BS-345-DSE-860-1F2 PC1035 1000 46.700000 5023 AX-532-FED-452-2Z7 BU2075 500 46.700000 5023 AX-532-FED-452-2Z7 BU1032 200 46.700000 5023 AX-532-FED-452-2Z7 BU7832 150 46.700000 5023 AX-532-FED-452-2Z7 PS7777 125 46.700000 5023 NF-123-ADS-642-9G3 TC7777 1000 46.700000 5023 NF-123-ADS-642-9G3 BU1032 1000 46.700000 5023 NF-123-ADS-642-9G3 PC1035 750 46.700000 7131 Fsoap867 BU1032 200 46.700000 7066 BA52498 BU7832 100 46.700000 7066 BA71224 PS7777 200 46.700000 7066 BA71224 PC1035 300 46.700000 7066 BA71224 TC7777 350 46.700000 5023 ZD-123-DFG-752-9G8 PS2091 1000 46.700000 7067 NB-3.142 PS2091 200 46.700000 7067 NB-3.142 PS7777 250 46.700000 7067 NB-3.142 PS3333 345 46.700000 7067 NB-3.142 BU7832 360 46.700000Tables in the pubs2 database 692 Adaptive Server Enterprise 5023 XS-135-DER-432-8J2 PS2091 845 46.700000 5023 XS-135-DER-432-8J2 PS7777 581 46.700000 5023 ZZ-999-ZZZ-999-0A0 PS1372 375 46.700000 7067 NB-3.142 BU1111 175 46.700000 5023 XS-135-DER-432-8J2 BU7832 885 46.700000 5023 ZD-123-DFG-752-9G8 BU7832 900 46.700000 5023 AX-532-FED-452-2Z7 TC4203 550 46.700000 7131 Fsoap867 TC4203 350 46.700000 7896 234518 TC4203 275 46.700000 7066 BA71224 TC4203 500 46.700000 7067 NB-3.142 TC4203 512 46.700000 7131 Fsoap867 MC3021 400 46.700000 5023 AX-532-FED-452-2Z7 PC8888 105 46.700000 5023 NF-123-ADS-642-9G3 PC8888 300 46.700000 7066 BA71224 PC8888 350 46.700000 7067 NB-3.142 PC8888 335 46.700000 7131 Asoap432 BU1111 500 46.700000 7896 234518 BU1111 340 46.700000 5023 AX-532-FED-452-2Z7 BU1111 370 46.700000 5023 ZD-123-DFG-752-9G8 PS3333 750 46.700000 8042 13-J-9 BU7832 300 51.700000 8042 13-E-7 BU2075 150 51.700000 8042 13-E-7 BU1032 300 51.700000 8042 13-E-7 PC1035 400 51.700000 8042 91-A-7 PS7777 180 51.700000 8042 13-J-9 TC4203 250 51.700000 8042 13-E-7 TC4203 226 51.700000 8042 13-E-7 MC3021 400 51.700000 8042 91-V-7 BU1111 390 51.700000 5023 AB-872-DEF-732-2Z1 MC3021 5000 50.000000 5023 NF-123-ADS-642-9G3 PC8888 2000 50.000000 5023 NF-123-ADS-642-9G3 BU2075 2000 50.000000 5023 GH-542-NAD-713-9F9 PC1035 2000 50.000000 5023 ZA-000-ASD-324-4D1 PC1035 2000 50.000000 5023 ZA-000-ASD-324-4D1 PS7777 1500 50.000000 5023 ZD-123-DFG-752-9G8 BU2075 3000 50.000000 5023 ZD-123-DFG-752-9G8 TC7777 1500 50.000000 stor_id ord_num title_id qty discountAPPENDIX A The pubs2 Database Transact-SQL User’s Guide 693 5023 ZS-645-CAT-415-1B2 BU2075 3000 50.000000 5023 ZS-645-CAT-415-1B2 BU2075 3000 50.000000 5023 XS-135-DER-432-8J2 PS3333 2687 50.000000 5023 XS-135-DER-432-8J2 TC7777 1090 50.000000 5023 XS-135-DER-432-8J2 PC1035 2138 50.000000 5023 ZZ-999-ZZZ-999-0A0 MC2222 2032 50.000000 5023 ZZ-999-ZZZ-999-0A0 BU1111 1001 50.000000 5023 ZA-000-ASD-324-4D1 BU1111 1100 50.000000 5023 NF-123-ADS-642-9G3 BU7832 1400 50.000000 5023 BS-345-DSE-860-1F2 TC4203 2700 50.000000 5023 GH-542-NAD-713-9F9 TC4203 2500 50.000000 5023 NF-123-ADS-642-9G3 TC4203 3500 50.000000 5023 BS-345-DSE-860-1F2 MC3021 4500 50.000000 5023 AX-532-FED-452-2Z7 MC3021 1600 50.000000 5023 NF-123-ADS-642-9G3 MC3021 2550 50.000000 5023 ZA-000-ASD-324-4D1 MC3021 3000 50.000000 5023 ZS-645-CAT-415-1B2 MC3021 3200 50.000000 5023 BS-345-DSE-860-1F2 BU2075 2200 50.000000 5023 GH-542-NAD-713-9F9 BU1032 1500 50.000000 5023 ZZ-999-ZZZ-999-0A0 PC8888 1005 50.000000 7896 124152 BU2075 42 50.500000 7896 124152 PC1035 25 50.500000 7131 Asoap132 BU2075 35 50.500000 7067 NB-1.142 PC1035 34 50.500000 7067 NB-1.142 TC4203 53 50.500000 8042 12-F-9 BU2075 30 55.500000 8042 12-F-9 BU1032 94 55.500000 7066 BA27618 BU2075 200 57.200000 7896 124152 TC4203 350 57.200000 7066 BA27618 TC4203 230 57.200000 7066 BA27618 MC3021 200 57.200000 7131 Asoap132 MC3021 137 57.200000 7067 NB-1.142 MC3021 270 57.200000 7067 NB-1.142 BU2075 230 57.200000 7131 Asoap132 BU1032 345 57.200000 7067 NB-1.142 BU1032 136 57.200000 8042 12-F-9 TC4203 300 62.200000 stor_id ord_num title_id qty discountTables in the pubs2 database 694 Adaptive Server Enterprise sales table sales is defined as follows: create table sales (stor_id char(4) not null, ord_num varchar(20) not null, date datetime not null) Its primary keys are stor_id and ord_num: sp_primarykey sales, stor_id, ord_num Its stor_id column is a foreign key to stores: sp_foreignkey sales, stores, stor_id Table A-6 lists the contents of sales: 8042 12-F-9 MC3021 270 62.200000 8042 12-F-9 PC1035 133 62.200000 5023 AB-123-DEF-425-1Z3 TC4203 2500 60.500000 5023 AB-123-DEF-425-1Z3 BU2075 4000 60.500000 6380 342157 BU2075 200 57.200000 6380 342157 MC3021 250 57.200000 6380 356921 PS3333 200 46.700000 6380 356921 PS7777 500 46.700000 6380 356921 TC3218 125 46.700000 6380 234518 BU2075 135 46.700000 6380 234518 BU1032 320 46.700000 6380 234518 TC4203 300 46.700000 6380 234518 MC3021 400 46.700000 stor_id ord_num title_id qty discountAPPENDIX A The pubs2 Database Transact-SQL User’s Guide 695 Table A-6: sales table stores table stores is defined as follows: create table stores (stor_id char(4) not null, stor_id ord_num date 5023 AB-123-DEF-425-1Z3 Oct 31 1995 5023 AB-872-DEF-732-2Z1 Nov 6 1995 5023 AX-532-FED-452-2Z7 Dec 1 1996 5023 BS-345-DSE-860-1F2 Dec 12 1996 5023 GH-542-NAD-713-9F9 Feb 15 1997 5023 NF-123-ADS-642-9G3 Mar 18 1997 5023 XS-135-DER-432-8J2 Mar 21 1997 5023 ZA-000-ASD-324-4D1 Jul 27 1994 5023 ZD-123-DFG-752-9G8 Mar 21 1997 5023 ZS-645-CAT-415-1B2 Mar 21 1997 5023 ZZ-999-ZZZ-999-0A0 Mar 21 1997 6380 342157 Dec 13 1994 6380 356921 Feb 17 1995 7066 BA27618 Oct 12 1996 7066 BA52498 Oct 27 1995 7066 BA71224 Aug 5 1996 7067 NB-1.142 Jan 2 1997 7067 NB-3.142 Jun 13 1995 7131 Asoap132 Nov 16 1996 7131 Asoap432 Dec 20 1995 7131 Fsoap867 Sep 8 1996 7896 124152 Aug 14 1996 7896 234518 Feb 14 1997 8042 12-F-9 Jul 13 1996 8042 13-E-7 May 23 1995 8042 13-J-9 Jan 13 1997 8042 55-V-7 Feb 20 1997 8042 91-A-7 Mar 20 1997 8042 91-V-7 Mar 20 1997Tables in the pubs2 database 696 Adaptive Server Enterprise stor_name varchar(40) not null, stor_address varchar(40) null, city varchar(20) null, state char(2) null, country varchar(12) null, postalcode char(10) null, payterms varchar(12) null) Its primary key is stor_id: sp_primarykey stores, stor_id Table A-7 lists the contents of stores: Table A-7: stores table roysched table roysched is defined as follows: create table roysched title_id tid not null, lorange int null, hirange int null, royalty int null) Its primary key is title_id: sp_primarykey roysched, title_id Its title_id column is a foreign key to titles: stor_id stor_name stor_address city state country postalcode payterms 7066 Barnum’s 567 Pasadena Ave. Tustin CA USA 92789 Net 30 7067 News & Brews 577 First St. Los Gatos CA USA 96745 Net 30 7131 Doc-U-Mat: Quality Laundry and Books 24-A Avrogado Way Remulade WA USA 98014 Net 60 8042 Bookbeat 679 Carson St. Portland OR USA 89076 Net 30 6380 Eric the Read Books 788 Catamaugus Ave. Seattle WA USA 98056 Net 60 7896 Fricative Bookshop 89 Madison St. Fremont CA USA 90019 Net 60 5023 Thoreau Reading Discount Chain 20435 Walden Expressway Concord MA USA 01776 Net 60APPENDIX A The pubs2 Database Transact-SQL User’s Guide 697 sp_foreignkey roysched, titles, title_id Its nonclustered index for the title_id column is defined as: create nonclustered index titleidind on roysched (title_id) Table A-8 lists the contents of roysched:Tables in the pubs2 database 698 Adaptive Server Enterprise Table A-8: roysched table title_id lorange hirange royalty BU1032 0 5000 10 BU1032 5001 50000 12 PC1035 0 2000 10 PC1035 2001 3000 12 PC1035 3001 4000 14 PC1035 4001 10000 16 PC1035 10001 50000 18 BU2075 0 1000 10 BU2075 1001 3000 12 BU2075 3001 5000 14 BU2075 5001 7000 16 BU2075 7001 10000 18 BU2075 10001 12000 20 BU2075 12001 14000 22 BU2075 14001 50000 24 PS2091 0 1000 10 PS2091 1001 5000 12 PS2091 5001 10000 14 PS2091 10001 50000 16 PS2106 0 2000 10 PS2106 2001 5000 12 PS2106 5001 10000 14 PS2106 10001 50000 16 MC3021 0 1000 10 MC3021 1001 2000 12 MC3021 2001 4000 14 MC3021 4001 6000 16 MC3021 6001 8000 18 MC3021 8001 10000 20 MC3021 10001 12000 22 MC3021 12001 50000 24 TC3218 0 2000 10 TC3218 2001 4000 12 TC3218 4001 6000 14 TC3218 6001 8000 16 TC3218 8001 10000 18APPENDIX A The pubs2 Database Transact-SQL User’s Guide 699 TC3218 10001 12000 20 TC3218 12001 14000 22 TC3218 14001 50000 24 PC8888 0 5000 10 PC8888 5001 10000 12 PC8888 10001 15000 14 PC8888 15001 50000 16 PS7777 0 5000 10 PS7777 5001 50000 12 PS3333 0 5000 10 PS3333 5001 10000 12 PS3333 10001 15000 14 PS3333 15001 50000 16 BU1111 0 4000 10 BU1111 4001 8000 12 BU1111 8001 10000 14 BU1111 12001 16000 16 BU1111 16001 20000 18 BU1111 20001 24000 20 BU1111 24001 28000 22 BU1111 28001 50000 24 MC2222 0 2000 10 MC2222 2001 4000 12 MC2222 4001 8000 14 MC2222 8001 12000 16 MC2222 8001 12000 16 MC2222 12001 20000 18 MC2222 20001 50000 20 TC7777 0 5000 10 TC7777 5001 15000 12 TC7777 15001 50000 14 TC4203 0 2000 10 TC4203 2001 8000 12 TC4203 8001 16000 14 TC4203 16001 24000 16 TC4203 24001 32000 18 TC4203 32001 40000 20 title_id lorange hirange royaltyTables in the pubs2 database 700 Adaptive Server Enterprise discounts table discounts is defined as follows: create table discounts (discounttype varchar(40) not null, stor_id char(4) null, lowqty smallint null, highqty smallint null, discount float not null) Its primary keys are discounttype and stor_id: sp_primarykey discounts, discounttype, stor_id Its stor_id is a foreign key to stores: sp_foreignkey discounts, stores, stor_id Table A-9 lists the contents of discounts: Table A-9: discounts table TC4203 40001 50000 22 BU7832 0 5000 10 BU7832 5001 10000 12 BU7832 10001 15000 14 BU7832 15001 20000 16 BU7832 20001 25000 18 BU7832 25001 30000 20 BU7832 30001 35000 22 BU7832 35001 50000 24 PS1372 0 10000 10 PS1372 10001 20000 12 PS1372 20001 30000 14 PS1372 30001 40000 16 PS1372 40001 50000 18 title_id lorange hirange royalty discounttype stor_id lowqty highqty discount Initial Customer 8042 NULL NULL 10.5 Volume Discount NULL 100 1001 6.7 Huge Volume Discount NULL 1001 NULL 10 Customer Discount 8042 NULL NULL 5APPENDIX A The pubs2 Database Transact-SQL User’s Guide 701 blurbs table blurbs is defined as follows: create table blurbs (au_id id not null, copy text null) Its primary key is au_id: sp_primarykey blurbs, au_id Its au_id column is a foreign key to authors: sp_foreignkey blurbs, authors, au_id Table A-10 lists the contents of blurbs: Table A-10: blurbs table au_id copy 486-29-1786 If Chastity Locksley didn’t exist, this troubled world would have created her! Not only did she master the mystic secrets of inner strength to conquer adversity when she encountered it in life, but also, after “reinventing herself,” as she says, by writing “Emotional Security: A New Algorithm” following the devastating loss of her cat, Old Algorithm, she founded Publish or Perish, the page-by-page, day-by-day, write-yourself-to-wellness encounter workshops franchise empire, the better to share her inspiring discoveries with us all. Her “Net Etiquette,” a brilliant social treatise in its own right and a fabulous pun, is the only civilized alternative to the gross etiquette often practiced on the public networks. 648-92-1872 A chef’s chef and a raconteur’s raconteur, Reginald Blotchet-Halls calls London his second home. “Th’ palace kitchen’s me first ‘ome, act’lly!” Blotchet-Halls’ astounding ability to delight our palates with palace delights is matched only by his equal skill in satisfying our perpetual hunger for delicious back-stairs gossip by serving up tidbits and entrees literally fit for a king! 998-72-3567 Albert Ringer was born in a trunk to circus parents, but another kind of circus trunk played a more important role in his life years later. He grew up as an itinerant wrestler and roustabout in the renowned Ringer Brothers and Betty and Bernie’s Circus. Once known in the literary world only as Anne Ringer’s wrestling brother, he became a writer while recuperating from a near-fatal injury received during a charity benefit bout with a gorilla. “Slingshotting” himself from the ring ropes, Albert flew over the gorilla’s head and would have landed head first on the concrete. He was saved from certain death by Nana, an elephant he had befriended as a child, who caught him in her trunk. Nana held him so tightly that three ribs cracked and he turned blue from lack of oxygen. “I was delirious. I had an out-of-body experience! My whole life passed before me eyes. I promised myself ‘If I get through this, I’ll use my remaining time to share what I learned out there.’ I owe it all to Nana!”Tables in the pubs2 database 702 Adaptive Server Enterprise au_pix table au_pix is defined as follows: create table au_pix (au_id char(11) not null, pic image null, format_type char(11) null, bytesize int null, pixwidth_hor char(14) null, pixwidth_vert char(14) null) 899-46-2035 Anne Ringer ran away from the circus as a child. A university creative writing professor and her family took Anne in and raised her as one of their own. In this warm and television-less setting she learned to appreciate the great classics of literature. The stream of aspiring and accomplished writers that flowed constantly through the house confirmed her repudiation of the circus family she’d been born into: “Barbarians!” The steadily growing recognition of her literary work was, to her, vindication. When her brother’s brush with death brought them together after many years, she took advantage of life’s crazy chance thing and broke the wall of anger that she had constructed to separate them. Together they wrote, “Is Anger the Enemy?” an even greater blockbuster than her other collaborative work, with Michel DeFrance, “The Gourmet Microwave.” 672-71-3249 They asked me to write about myself and my book, so here goes: I started a restaurant called “de Gustibus” with two of my friends. We named it that because you really can’t discuss taste. We’re very popular with young business types because we’re young business types ourselves. Whenever we tried to go out to eat in a group we always got into these long tiresome negotiations: “I just ate Italian,” or “I ate Greek yesterday,” or “I NEVER eat anything that’s not organic!” Inefficient. Not what business needs today. So, it came to us that we needed a restaurant we could all go to every day and not eat the same thing twice in a row maybe for a year! We thought, “Hey, why make people choose one kind of restaurant over another, when what they really want is a different kind of food?” At de Gustibus you can eat Italian, Chinese, Japanese, Greek, Russian, Tasmanian, Iranian, and on and on all at the same time. You never have to choose. You can even mix and match! We just pooled our recipes, opened the doors, and never looked back. We’re a big hit, what can I say? My recipes in “Sushi, Anyone?” are used at de Gustibus. They satisfy crowds for us every day. They will work for you, too. Period! 409-56-7008 Bennet was the classic too-busy executive. After discovering computer databases, he now has the time to run several successful businesses and sit on three major corporate boards. Bennet also donates time to community service organizations. Miraculously, he also finds time to write and market executive-oriented, in-depth computer hardware and software reviews. “I’m hyperkinetic, so being dynamic and fast-moving is a piece of cake. But being organized isn’t easy for me or for anyone I know. There’s just one word for that: ‘databases!’ Databases can cure you or kill you. If you get the right one, you can be like me. If you get the wrong one, watch out. Read my book!” au_id copyAPPENDIX A The pubs2 Database Transact-SQL User’s Guide 703 Its primary key is au_id: sp_primarykey au_pix, au_id Its au_id column is a foreign key to authors: sp_foreignkey au_pix, authors, au_id Table A-11 lists the contents of au_pix: Table A-11: au_pix table The pic column contains binary data, which is not reproduced in its entirety in this table. The pictures represented by this data are shown on the next page. Since the image data (six pictures, two each in PICT, TIF, and Sunraster file formats) is quite large, you should run the installpix2 script only if you want to use or test the image datatype. The image data is supplied to show how Sybase stores image data. Sybase does not supply any tools for displaying image data: you must use the appropriate screen graphics tools in order to display the images once you have extracted them from the database. au_id pic format_type bytesize pixwidth_hor pixwidth_vert 409-56-7008 0x0000... PICT 30220 626 635 486-29-1786 0x59a6... Sunraster 27931 647 640 648-92-1872 0x59a6... Sunraster 36974 647 640 672-71-3249 0x000a... PICT 13487 654 639 899-46-2035 0x4949... TIF 52023 648 641 998-72-3567 0x4949... TIF 52336 653 637Tables in the pubs2 database 704 Adaptive Server Enterprise Figure A-1: Author portraits from the au_pix tableAPPENDIX A The pubs2 Database Transact-SQL User’s Guide 705 Diagram of the pubs2 database Figure A-2: Diagram of the pubs2 databaseDiagram of the pubs2 database 706 Adaptive Server EnterpriseTransact-SQL User’s Guide 707 A P P E N D I X B The pubs3 Database This chapter describes the sample database pubs3. This database contains the tables publishers, authors, titles, titleauthor, salesdetail, sales, stores, store_employees, discounts, roysched, and blurbs. The pubs3 database also contains primary and foreign keys, rules, defaults, views, triggers, and stored procedures. A diagram of the pubs3 database appears in Figure B-1 on page 739. For information about installing pubs3, see the configuration guide for your platform. Tables in the pubs3 database The following sections describe each pubs3 table. In the tables, each column header specifies the column name, its datatype (including any user-defined datatypes), its null or not null status, and how it uses referential integrity. The column header also specifies any defaults, rules, triggers, and indexes that affect the column. publishers table publishers is defined as follows: create table publishers (pub_id char(4) not null, pub_name varchar(40) not null, city varchar(20) null, state char(2) null, unique nonclustered (pub_id)) Its pub_idrule rule is defined as:Tables in the pubs3 database 708 Adaptive Server Enterprise create rule pub_idrule as @pub_id in ("1389", "0736", "0877", "1622", "1756") or @pub_id like "99[0-9][0-9]" Table B-1 lists the contents of publishers: Table B-1: publishers table authors table authors is defined as follows: create table authors (au_id id not null, au_lname varchar(40) not null, au_fname varchar(20) not null, phone char(12) not null, address varchar(40) null, city varchar(20) null, state char(2) null, country varchar(12) null, postalcode char(10) null, unique nonclustered (au_id)) Its nonclustered index for the au_lname and au_fname columns is defined as: create nonclustered index aunmind on authors (au_lname, au_fname) The phone column has the following default: create default phonedflt as "UNKNOWN" sp_bindefault phonedft, "authors.phone" The following view uses authors: create view titleview as select title, au_ord, au_lname, price, num_sold, pub_id from authors, titles, titleauthor where authors.au_id = titleauthor.au_id pub_id pub_name city state 0736 New Age Books Boston MA 0877 Binnet & Hardley Washington DC 1389 Algodata Infosystems Berkeley CAAPPENDIX B The pubs3 Database Transact-SQL User’s Guide 709 and titles.title_id = titleauthor.title_id Table B-2 lists the contents of authors: Table B-2: authors table au_id au_lname au_fname phone address city state country postalcode 172- 32- 1176 White Johnson 408 496- 7223 10932 Bigge Rd. Menlo Park CA USA 94025 213- 46- 8915 Green Marjorie 510 986- 7020 309 63rd St. #411 Oakland CA USA 94618 238- 95- 7766 Carson Cheryl 510 548- 7723 589 Darwin Ln. Berkeley CA USA 94705 267- 41- 2394 O’Leary Michael 408 286- 2428 22 Cleveland Av. #14 San Jose CA USA 95128 274- 80- 9391 Straight Dick 510 834- 2919 5420 College Av. Oakland CA USA 94609 341- 22- 1782 Smith Meander 913 843- 0462 10 Mississippi Dr. Lawrence KS USA 66044 409- 56- 7008 Bennet Abraham 510 658- 9932 6223 Bateman St. Berkeley CA USA 94705 427- 17- 2319 Dull Ann 415 836- 7128 3410 Blonde St. Palo Alto CA USA 94301 472- 27- 2349 Gringlesby Burt 707 938- 6445 PO Box 792 Covelo CA USA 95428 486- 29- 1786 Locksley Chastity 415 585- 4620 18 Broadway Av. San Francisco CA USA 94130 527- 72- 3246 Greene Morningstar 615 297- 2723 22 Graybar House Rd. Nashville TN USA 37215 648- 92- 1872 BlotchetHalls Reginald 503 745- 6402 55 Hillsdale Bl. Corvallis OR USA 97330Tables in the pubs3 database 710 Adaptive Server Enterprise titles table titles is defined as follows: create table titles (title_id tid not null, title varchar(80) not null, 672- 71- 3249 Yo k o mo to Ak ik o 4 1 5 935- 4228 3 Silver Ct. Walnut Creek CA USA 94595 712- 45- 1867 del Castillo Innes 615 996- 8275 2286 Cram Pl. #86 Ann Arbor MI USA 48105 722- 51- 5454 DeFrance Michel 219 547- 9982 3 Balding Pl. Gary IN USA 46403 724- 08- 9931 Stringer Dirk 510 843- 2991 5420 Telegraph Av. Oakland CA USA 94609 724- 80- 9391 MacFeather Stearns 510 354- 7128 44 Upland Hts. Oakland CA USA 94612 756- 30- 7391 Karsen Livia 510 534- 9219 5720 McAuley St. Oakland CA USA 94609 807- 91- 6654 Panteley Sylvia 301 946- 8853 1956 Arlington Pl. Rockville MD USA 20853 846- 92- 7186 Hunter Sheryl 415 836- 7128 3410 Blonde St. Palo Alto CA USA 94301 893- 72- 1158 McBadden Heather 707 448- 4982 301 Putnam Vacaville CA USA 95688 899- 46- 2035 Ringer Anne 801 826- 0752 67 Seventh Av. Salt Lake City UT USA 84152 998- 72- 3567 Ringer Albert 801 826- 0752 67 Seventh Av. Salt Lake City UT USA 84152 au_id au_lname au_fname phone address city state country postalcodeAPPENDIX B The pubs3 Database Transact-SQL User’s Guide 711 type char(12) not null, pub_id char(4) null references publishers(pub_id), price money null, advance numeric(12,2) null, num_sold int null, notes varchar(200) null, pubdate datetime not null, contract bit not null, unique nonclustered (title_id)) Its nonclustered index for the title column is defined as: create nonclustered index titleind on titles (title) Its title_idrule is defined as: create rule title_idrule as @title_id like "BU[0-9][0-9][0-9][0-9]" or @title_id like "[MT]C[0-9][0-9][0-9][0-9]" or @title_id like "P[SC][0-9][0-9][0-9][0-9]" or @title_id like "[A-Z][A-Z]xxxx" or @title_id like "[A-Z][A-Z]yyyy" The type column has the following default: create default typedflt as "UNDECIDED" sp_bindefault typedflt, "titles.type" The pubdate column has this default: create default datedflt as getdate() sp_bindefault datedflt, "titles.pubdate" titles uses the following trigger: create trigger deltitle on titles for delete as if (select count(*) from deleted, salesdetail where salesdetail.title_id = deleted.title_id) >0 begin rollback transaction print "You can’t delete a title with sales." end The following view uses titles:Tables in the pubs3 database 712 Adaptive Server Enterprise create view titleview as select title, au_ord, au_lname, price, num_sold, pub_id from authors, titles, titleauthor where authors.au_id = titleauthor.au_id and titles.title_id = titleauthor.title_id Table B-3 lists the contents of titles: Table B-3: titles table title_id title type pub- _id price advance num_- sold notes pubdate contract BU1032 The Busy Executive’s Database Guide business 1389 19.99 5000.00 4095 An overview of available database systems with emphasis on common business applications. Illustrated. Jun 12, 1986 1 BU1111 Cooking with Computers: Surreptitious Balance Sheets business 1389 11.95 5000.00 3876 Helpful hints on how to use your electronic resources to the best advantage. Jun 9, 1988 1 BU2075 You Can Combat Computer Stress! business 0736 2.99 10125.00 18722 The latest medical and psychological techniques for living with the electronic office. Easyto-understand explanations. Jun 30, 1985 1APPENDIX B The pubs3 Database Transact-SQL User’s Guide 713 BU7832 Straight Talk About Computers business 1389 19.99 5000.00 4095 Annotated analysis of what computers can do for you: a nohype guide for the critical user. Jun 22, 1987 1 MC2222 Silicon Va lle y Gastronomic Treats mod_- cook 0877 19.99 0.00 2032 Favorite recipes for quick, easy, and elegant meals; tried and tested by people who never have time to eat, let alone cook. Jun 9, 1989 1 MC3021 The Gourmet Microwave mod_- cook 0877 2.99 15000.00 22246 Traditional French gourmet recipes adapted for modern microwave cooking. Jun 18, 1985 1 PC1035 But Is It User Friendly? popular_ comp 1389 22.95 7000.00 8780 A survey of software for the naive user, focusing on the “friendliness” of each. Jun 30, 1986 1 MC3026 The Psychology of Computer Cooking UNDECIDED 0877 NULL NULL NULL NULL Jul 24, 1991 0 title_id title type pub- _id price advance num_- sold notes pubdate contractTables in the pubs3 database 714 Adaptive Server Enterprise PC8888 Secrets of Silicon Valley popular_ comp 1389 20.00 8000.00 4095 Muckraking reporting by two courageous women on the world’s largest computer hardware and software manufacturers. Jun 12, 1987 1 PC9999 Net Etiquette popular_ comp 1389 NULL NULL NULL A must-read for computer conferencing debutantes! Jul 24, 1996 0 PS1372 Computer Phobic and Non-Phobic Individuals: Behavior Variations psychology 0877 21.59 7000.00 375 A must for the specialist, this book examines the difference between those who hate and fear computers and those who think they are swell. Oct 21, 1990 1 title_id title type pub- _id price advance num_- sold notes pubdate contractAPPENDIX B The pubs3 Database Transact-SQL User’s Guide 715 PS2091 Is Anger the Enemy? psychology 0736 10.95 2275.00 2045 Carefully researched study of the effects of strong emotions on the body. Metabolic charts included. Jun 15, 1989 1 PS2106 Life Without Fear psychology 0736 7.00 6000.00 111 New exercise, meditation, and nutritional techniques that can reduce the shock of daily interactions. Popular audience. Sample menus included. Exercise video available separately. Oct 5, 1990 1 PS3333 Prolonged Data Deprivation: Four Case Studies psychology 0736 19.99 2000.00 4072 What happens when the data runs dry? Searching evaluations of informationshortage effects on heavy users. Jun 12, 1988 1 title_id title type pub- _id price advance num_- sold notes pubdate contractTables in the pubs3 database 716 Adaptive Server Enterprise PS7777 Emotional Security: A New Algorithm psychology 0736 7.99 4000.00 3336 Protecting yourself and your loved ones from undue emotional stress in the modern world. Use of computer and nutritional aids emphasized. Jun 12, 1988 1 TC3218 Onions, Leeks, and Garlic: Cooking Secrets of the Mediterranean trad_coo k 0877 20.95 7000.00 375 Profusely illustrated in color, this makes a wonderful gift book for a cuisineoriented friend. Oct 21, 1990 1 TC4203 Fifty Years in Buckingham Palace Kitchens trad_coo k 0877 11.95 4000.00 15096 More anecdotes from the Queen’s favorite cook describing life among English royalty. Recipes, techniques, tender vignettes. Jun 12, 1985 1 title_id title type pub- _id price advance num_- sold notes pubdate contractAPPENDIX B The pubs3 Database Transact-SQL User’s Guide 717 titleauthor table titleauthor is defined as follows: create table titleauthor (au_id id not null references authors(au_id), title_id tid not null references titles(title_id), au_ord tinyint null, royaltyper int null) Its nonclustered index for the au_id column is defined as: create nonclustered index auidind on titleauthor(au_id) Its nonclustered index for the title_id column is defined as: create nonclustered index titleidind on titleauthor(title_id) The following view uses titleauthor: TC7777 Sushi, Anyone? trad_coo k 0877 14.99 8000.00 4095 Detailed instructions on improving your position in life by learning how to make authentic Japanese sushi in your spare time. 5-10% increase in number of friends per recipe reported from beta test. Jun 12, 1987 1 title_id title type pub- _id price advance num_- sold notes pubdate contractTables in the pubs3 database 718 Adaptive Server Enterprise create view titleview as select title, au_ord, au_lname, price, num_sold, pub_id from authors, titles, titleauthor where authors.au_id = titleauthor.au_id and titles.title_id = titleauthor.title_id The following procedure uses titleauthor: create procedure byroyalty @percentage int as select au_id from titleauthor where titleauthor.royaltyper = @percentage Table B-4 lists the contents of titleauthor:APPENDIX B The pubs3 Database Transact-SQL User’s Guide 719 Table B-4: titleauthor table salesdetail table salesdetail is defined as follows: create table salesdetail (stor_id char(4) not null references sales(stor_id), ord_num numeric(6,0) references sales(ord_num), title_id tid not null references titles(title_id), au_id title_id au_ord royaltyper 172-32-1176 PS3333 1 100 213-46-8915 BU1032 2 40 213-46-8915 BU2075 1 100 238-95-7766 PC1035 1 100 267-41-2394 BU1111 2 40 267-41-2394 TC7777 2 30 274-80-9391 BU7832 1 100 409-56-7008 BU1032 1 60 427-17-2319 PC8888 1 50 472-27-2349 TC7777 3 30 486-29-1786 PC9999 1 100 486-29-1786 PS7777 1 100 648-92-1872 TC4203 1 100 672-71-3249 TC7777 1 40 712-45-1867 MC2222 1 100 722-51-5454 MC3021 1 75 724-80-9391 BU1111 1 60 724-80-9391 PS1372 2 25 756-30-7391 PS1372 1 75 807-91-6654 TC3218 1 100 846-92-7186 PC8888 2 50 899-46-2035 MC3021 2 25 899-46-2035 PS2091 2 50 998-72-3567 PS2091 1 50 998-72-3567 PS2106 1 100Tables in the pubs3 database 720 Adaptive Server Enterprise qty smallint not null, discount float not null) Its nonclustered index for the title_id column is defined as: create nonclustered index titleidind on salesdetail (title_id) Its nonclustered index for the stor_id column is defined as: create nonclustered index salesdetailind on salesdetail (stor_id) Its title_idrule rule is defined as: create rule title_idrule as @title_id like "BU[0-9][0-9][0-9][0-9]" or @title_id like "[MT]C[0-9][0-9][0-9][0-9]" or @title_id like "P[SC][0-9][0-9][0-9][0-9]" or @title_id like "[A-Z][A-Z]xxxx" or @title_id like "[A-Z][A-Z]yyyy" salesdetail uses the following trigger: create trigger totalsales_trig on salesdetail for insert, update, delete as /* Save processing: return if there are no rows affected */ if @@rowcount = 0 begin return end /* add all the new values */ /* use isnull: a null value in the titles table means ** "no sales yet" not "sales unknown" */ update titles set num_sold = isnull(num_sold, 0) + (select sum(qty) from inserted where titles.title_id = inserted.title_id) where title_id in (select title_id from inserted) /* remove all values being deleted or updated */ update titles set num_sold = isnull(num_sold, 0) - (select sum(qty) from deleted where titles.title_id = deleted.title_id) where title_id in (select title_id from deleted)APPENDIX B The pubs3 Database Transact-SQL User’s Guide 721 Table B-5 lists the contents of salesdetail: Tables in the pubs3 database 722 Adaptive Server Enterprise Table B-5: salesdetail table stor_id ord_num title_id qty discount 7896 100014 TC3218 75 40.000000 7896 100014 TC7777 75 40.000000 7131 100017 TC3218 50 40.000000 7131 100017 TC7777 80 40.000000 5023 100020 TC3218 85 40.000000 8042 100016 PS3333 90 45.000000 8042 100016 TC3218 40 45.000000 8042 100016 PS2106 30 45.000000 8042 100023 PS2106 50 45.000000 8042 100015 PS2106 31 45.000000 8042 100016 MC3021 69 45.000000 5023 100009 PC1035 1000 46.700000 5023 100007 BU2075 500 46.700000 5023 100007 BU1032 200 46.700000 5023 100007 BU7832 150 46.700000 5023 100007 PS7777 125 46.700000 5023 100018 TC7777 1000 46.700000 5023 100018 BU1032 1000 46.700000 5023 100018 PC1035 750 46.700000 7131 100004 BU1032 200 46.700000 7066 100012 BU7832 100 46.700000 7066 100021 PS7777 200 46.700000 7066 100021 PC1035 300 46.700000 7066 100021 TC7777 350 46.700000 5023 100025 PS2091 1000 46.700000 7067 100019 PS2091 200 46.700000 7067 100019 PS7777 250 46.700000 7067 100019 PS3333 345 46.700000 7067 100019 BU7832 360 46.700000 5023 100020 PS2091 845 46.700000 5023 100020 PS7777 581 46.700000 5023 100027 PS1372 375 46.700000 7067 100019 BU1111 175 46.700000 5023 100020 BU7832 885 46.700000 5023 100025 BU7832 900 46.700000 5023 100007 TC4203 550 46.700000APPENDIX B The pubs3 Database Transact-SQL User’s Guide 723 7131 100004 TC4203 350 46.700000 7896 100014 TC4203 275 46.700000 7066 100021 TC4203 500 46.700000 7067 100019 TC4203 512 46.700000 7131 100004 MC3021 400 46.700000 5023 100007 PC8888 105 46.700000 5023 100018 PC8888 300 46.700000 7066 100021 PC8888 350 46.700000 7067 100019 PC8888 335 46.700000 7131 100017 BU1111 500 46.700000 7896 100014 BU1111 340 46.700000 5023 100007 BU1111 370 46.700000 5023 100025 PS3333 750 46.700000 8042 100014 BU7832 300 51.700000 8042 100013 BU2075 150 51.700000 8042 100013 BU1032 300 51.700000 8042 100013 PC1035 400 51.700000 8042 100016 PS7777 180 51.700000 8042 100014 TC4203 250 51.700000 8042 100013 TC4203 226 51.700000 8042 100013 MC3021 400 51.700000 8042 100023 BU1111 390 51.700000 5023 100003 MC3021 5000 50.000000 5023 100018 PC8888 2000 50.000000 5023 100018 BU2075 2000 50.000000 5023 100010 PC1035 2000 50.000000 5023 100022 PC1035 2000 50.000000 5023 100022 PS7777 1500 50.000000 5023 100025 BU2075 3000 50.000000 5023 100025 TC7777 1500 50.000000 5023 100026 BU2075 3000 50.000000 5023 100026 BU2075 3000 50.000000 5023 100020 PS3333 2687 50.000000 5023 100020 TC7777 1090 50.000000 5023 100020 PC1035 2138 50.000000 5023 100027 MC2222 2032 50.000000 5023 100027 BU1111 1001 50.000000 stor_id ord_num title_id qty discountTables in the pubs3 database 724 Adaptive Server Enterprise 5023 100022 BU1111 1100 50.000000 5023 100018 BU7832 1400 50.000000 5023 100009 TC4203 2700 50.000000 5023 100010 TC4203 2500 50.000000 5023 100018 TC4203 3500 50.000000 5023 100009 MC3021 4500 50.000000 5023 100007 MC3021 1600 50.000000 5023 100018 MC3021 2550 50.000000 5023 100022 MC3021 3000 50.000000 5023 100026 MC3021 3200 50.000000 5023 100009 BU2075 2200 50.000000 5023 100010 BU1032 1500 50.000000 5023 100027 PC8888 1005 50.000000 7896 100013 BU2075 42 50.500000 7896 100013 PC1035 25 50.500000 7131 100005 BU2075 35 50.500000 7067 100011 PC1035 34 50.500000 7067 100011 TC4203 53 50.500000 8042 100015 BU2075 30 55.500000 8042 100015 BU1032 94 55.500000 7066 100001 BU2075 200 57.200000 7896 100013 TC4203 350 57.200000 7066 100001 TC4203 230 57.200000 7066 100001 MC3021 200 57.200000 7131 100005 MC3021 137 57.200000 7067 100011 MC3021 270 57.200000 7067 100011 BU2075 230 57.200000 7131 100005 BU1032 345 57.200000 7067 100011 BU1032 136 57.200000 8042 100015 TC4203 300 62.200000 8042 100015 MC3021 270 62.200000 8042 100015 PC1035 133 62.200000 5023 100002 TC4203 2500 60.500000 5023 100002 BU2075 4000 60.500000 6380 100028 BU2075 200 57.200000 6380 100028 MC3021 250 57.200000 6380 100029 PS3333 200 46.700000 stor_id ord_num title_id qty discountAPPENDIX B The pubs3 Database Transact-SQL User’s Guide 725 sales table sales is defined as follows: create table sales (stor_id char(4) not null references stores(stor_id), ord_num numeric(6,0) identity, date datetime not null, unique nonclustered (ord_num)) Table B-6 lists the contents of sales: 6380 100029 PS7777 500 46.700000 6380 100029 TC3218 125 46.700000 6380 100014 BU2075 135 46.700000 6380 100014 BU1032 320 46.700000 6380 100014 TC4203 300 46.700000 6380 100014 MC3021 400 46.700000 stor_id ord_num title_id qty discountTables in the pubs3 database 726 Adaptive Server Enterprise Table B-6: sales table stores table stores is defined as follows: create table stores (stor_id char(4) not null, stor_id ord_num date 5023 100002 Oct 31 1995 5023 100003 Nov 6 1995 5023 100007 Dec 1 1996 5023 100009 Dec 12 1996 5023 100010 Feb 15 1997 5023 100018 Mar 18 1997 5023 100020 Mar 21 1997 5023 100022 Jul 27 1994 5023 100025 Mar 21 1997 5023 100026 Mar 21 1997 5023 100027 Mar 21 1997 6380 100028 Dec 13 1994 6380 100029 Feb 17 1995 7066 100001 Oct 12 1996 7066 100012 Oct 27 1995 7066 100021 Aug 5 1996 7067 100008 Jan 2 1997 7067 100024 Jun 13 1995 7131 100006 Nov 16 1996 7131 100011 Dec 20 1995 7131 100019 Sep 8 1996 7896 100005 Aug 14 1996 7896 100017 Feb 14 1997 8042 100004 Jul 13 1996 8042 100013 May 23 1995 8042 100014 Jan 13 1997 8042 100015 Feb 20 1997 8042 100016 Mar 20 1997 8042 100023 Mar 20 1997APPENDIX B The pubs3 Database Transact-SQL User’s Guide 727 stor_name varchar(40) not null, stor_address varchar(40) null, city varchar(20) null, state char(2) null, country varchar(12) null, postalcode char(10) null, payterms varchar(12) null, unique nonclustered (stor_id)) Table B-7 lists the contents of stores: Table B-7: stores table store_employees table store_employees is defined as follows: create table store_employees (stor_id char(4) null references stores(stor_id), emp_id id not null, mgr_id id null references store_employees(emp_id), emp_lname varchar(40) not null, emp_fname varchar(20) not null, phone char(12) null, address varchar(40) null, city varchar(20) null, stor_id stor_name stor_address city state country postalcode payterms 7066 Barnum’s 567 Pasadena Ave. Tustin CA USA 92789 Net 30 7067 News & Brews 577 First St. Los Gatos CA USA 96745 Net 30 7131 Doc-U-Mat: Quality Laundry and Books 24-A Avrogado Way Remulade WA USA 98014 Net 60 8042 Bookbeat 679 Carson St. Portland OR USA 89076 Net 30 6380 Eric the Read Books 788 Catamaugus Ave. Seattle WA USA 98056 Net 60 7896 Fricative Bookshop 89 Madison St. Fremont CA USA 90019 Net 60 5023 Thoreau Reading Discount Chain 20435 Walden Expressway Concord MA USA 01776 Net 60Tables in the pubs3 database 728 Adaptive Server Enterprise state char(2) null, country varchar(12) null, postalcode varchar(10) null, unique nonclustered (emp_id)) Table B-8 lists the contents of store_employees: Table B-8: store_employees table stor- _id emp- _id mgr- _id emp_- lname emp_- fname phone address city state coun -try postalcode 7066 415- 92- 7301 415- 92- 7301 Chichikov P. 619 336- 8978 20 Alfalfa Ave. Twentynine Palms CA USA 92277 7066 202- 93- 0009 415- 92- 7301 Spindleshanks Daisy 619 336- 8900 14 Wild Cat Way Twentynine Palms CA USA 92277 7066 444- 89- 2342 415- 92- 7301 Ratsbane Ian 619 344- 92321 1827 Roadrunner Dr. Twentynine Palms CA USA 92278 7066 332- 78- 2382 415- 92- 7301 Bayless Chuck 619 777- 4356 7 Maynard Dr. Twentynine Palms CA USA 92277 7066 898- 00- 2383 415- 92- 7301 Pumpion Tammy 619 222- 3434 10089 Lazy Joe Ave. Twentynine Palms CA USA 92277 7066 222- 90- 3737 415- 92- 7301 Barnum Arthur 619 333- 3232 522 Lupine Ave. Twentynine Palms CA USA 92277 7066 939- 32- 1212 415- 92- 7301 Ronald Bill 619 333- 4550 69 Coyote Ct. Twentynine Palms CA USA 92277 7067 343- 38- 9494 343- 38- 9494 St. Augustine Fiona 408 222- 8383 17 Call of the Wild Rd. Los Gatos CA USA 95030 7067 222- 90- 3483 343- 38- 9494 Sebastian Basil 408 334- 8928 29 Dharma Rd. Los Gatos CA USA 95030 7067 121- 00- 3823 343- 38- 9494 Marchmain Albin 408 343- 8934 1001 Top of the Hill Ct. Los Gatos CA USA 95030 7067 232- 29- 8938 343- 38- 9494 Barlow Hilary 408 232- 3332 2 Topping Way Los Gatos CA USA 95032APPENDIX B The pubs3 Database Transact-SQL User’s Guide 729 7067 232- 89- 9393 343- 38- 9494 Dieuberi Gustav 408 675- 8938 30 Mount Madonna Rd. Los Gatos CA USA 95030 7131 565- 67- 3920 565- 67- 3920 Lavator Marie 206 328- 2838 14 Peter Grubb Rd. SE Renton WA USA 98058 7131 848- 34- 4838 565- 67- 3920 Sope Inez 206 438- 3434 1238 Index Ave. SE Renton WA USA 98058 7131 232- 38- 2232 565- 67- 3920 Tubb Wally 206 323- 2828 180 Moses Lane S Renton WA USA 98058 7131 111- 90- 3283 565- 67- 3920 Basin Chalker 206 323- 7777 192 Naches Ave. N Renton WA USA 98055 7131 323- 32- 4444 565- 67- 3920 Waters Johnny 206 323- 9020 1 Pelly Ave. N Renton WA USA 98055 7131 238- 32- 0079 238- 32- 0079 Scrubb Billy 206 444- 3232 90 Vas h io n St. NE Renton WA USA 98059 7131 349- 00- 9393 565- 67- 3920 Tuwel Terry 206 323- 3233 66 Sunset Blvd. SW Renton WA USA 98055 8042 723- 99- 9329 723- 99- 9329 Crookshank Flanner y 503 323- 9090 SW 222 Laber Ct. Portland OR USA 97236 8042 343- 32- 0034 723- 99- 9329 Sitwell Davenport 503 333- 9494 14 SE Krause Lane Portland OR USA 97236 8042 877- 12- 9393 723- 99- 9329 Bartholomew Curan 503 333- 9332 18 SE Knee St. Portland OR USA 97266 8042 323- 99- 0009 723- 99- 9329 Yad do Mar y 5 03 333- 4844 NE Klickitat St. Portland OR USA 97212 8042 434- 94- 3203 723- 99- 9329 Peacock Mavis 503 494- 3413 4978 SW Huns Rd. Portland OR USA 97223 stor- _id emp- _id mgr- _id emp_- lname emp_- fname phone address city state coun -try postalcodeTables in the pubs3 database 730 Adaptive Server Enterprise 8042 232- 94- 5885 723- 99- 9329 Baldwin Dorothy 503 333- 9494 9 N. Image Canoe Ave. Portland OR USA 97217 8042 323- 09- 5872 723- 99- 9329 Corbit P. 503 335- 3491 89 NW Industry St. Portland OR USA 97210 8042 323- 54- 3434 723- 99- 9329 Pilkinton Faith 503 333- 4531 18 SW Inez St. Portland OR USA 97224 8042 331- 90- 8484 723- 99- 9329 Botteghe Obscura 503 889- 2832 555 SW Keerins Ct. Portland OR USA 97223 8042 884- 32- 8282 723- 99- 9329 Martineau Tristan 503 323- 5954 346 N. Leade Rd. Portland OR USA 97203 8042 112- 90- 3829 723- 99- 9329 Laughton Karla 503 323- 5929 900 N. Magpie St. Portland OR USA 97202 8042 434- 23- 9292 723- 99- 9329 MacLeish Cochran 503 433- 9493 1722 SE Ogden Ct. Portland OR USA 97202 6380 433- 01- 3922 433- 01- 3922 Horgran Eric 206 323- 4983 18 Thud Dr. S. Seattle WA USA 98198 6380 232- 30- 9999 433- 01- 3922 Farnsdale Finwick 206 434- 4949 2 Bellevue Ave. Seattle WA USA 98118 6380 333- 90- 3828 433- 01- 3922 Wolfe Wanda 206 323- 3333 2 S. Boze St. #15 Seattle WA USA 98108 6380 322- 09- 2122 433- 01- 3922 Begude Nina 206 333- 9023 1297 W. Cay Way Seattle WA USA 98108 6380 342- 78- 2832 433- 01- 3922 Howe Saphron 206 323- 4933 9827 Des Moines Dr. Seattle WA USA 98108 6380 882- 00- 3234 433- 01- 3922 Salidin Uma 206 390- 8328 13 Echo Lake Place Seattle WA USA 98126 stor- _id emp- _id mgr- _id emp_- lname emp_- fname phone address city state coun -try postalcodeAPPENDIX B The pubs3 Database Transact-SQL User’s Guide 731 6380 321- 89- 8832 433- 01- 3922 Marsicano Evan 206 322- 9392 7 Dancer Ave. SW’ Seattle WA USA 98126 6380 762- 32- 5555 433- 01- 3922 Boulignini Gus 206 323- 9396 308 S. Fidalgo St. Seattle WA USA 98108 7896 433- 01- 3921 433- 01- 3921 Malraison Marcel 206 889- 9983 2298 Berry Dr. Fremont CA USA 94555 7896 322- 32- 8382 433- 01- 3921 West Diana 206 898- 3233 20-B Knute St. Fremont CA USA 94536 7896 328- 74- 8748 433- 01- 3921 Cazalis Mari 206 326- 6785 18 May Dr. #7 Fremont CA USA 94555 7896 325- 87- 6766 433- 01- 3921 Zorronius Gaius 206 363- 8988 1967 Claude Dr. Fremont CA USA 94555 7896 323- 67- 5646 433- 01- 3921 Podding Marvin 206 438- 7858 242 Ram Ct. #123 Fremont CA USA 94539 7896 673- 03- 6728 433- 01- 3921 Phelan Micky 206 323- 7676 1212 Spinn Ct. Fremont CA USA 94539 7896 326- 77- 6482 433- 01- 3921 Bokanowski Peter 206 432- 4832 13 Sparto Dr. Fremont CA USA 94539 7896 653- 48- 2975 433- 01- 3921 Poodals F.W. 206 387- 6863 739 Sendak Dr. Fremont CA USA 94538 7896 320- 37- 4682 433- 01- 3921 Scrubbs Randy 206 323- 3874 18 Washo Dr. #A Fremont CA USA 94539 7896 323- 67- 4762 433- 01- 3921 Mullins M. 206 382- 7862 1717 Zircon Ter. Fremont CA USA 94555 7896 326- 76- 3863 433- 01- 3921 Clarac Sebastia n 206 387- 6732 5622 Zin St. #78 Fremont CA USA 94539 stor- _id emp- _id mgr- _id emp_- lname emp_- fname phone address city state coun -try postalcodeTables in the pubs3 database 732 Adaptive Server Enterprise roysched table roysched is defined as follows: create table roysched title_id tid not null 5023 534- 92- 2910 534- 92- 2910 Armand Mary 510 323- 5478 1912 Badger Ln. Concord CA USA 94521 5023 342- 38- 2782 534- 92- 2910 Blanzat Gomez 510 382- 3828 4229 Tiffany Pl. Concord CA USA 94518 5023 322- 39- 3222 534- 92- 2910 Winate Patrick 510 322- 5873 16 Mahoo Ln. Concord CA USA 94521 5023 932- 20- 4389 534- 92- 2910 Burke Aldous 510 433- 4829 12 Ponder Dr. #4 Concord CA USA 94521 5023 322- 43- 2828 534- 92- 2910 Roughhead Jonatha n 510 323- 4782 2 Athos Ct. Concord CA USA 94521 5023 832- 32- 3289 534- 92- 2910 Johnson Alexis 510 323- 3824 927 Aramis Ct. Concord CA USA 94520 5023 432- 32- 4444 534- 92- 2910 Blitzstein Jack 510 323- 3874 2 Porthos Ct. Concord CA USA 94519 5023 543- 43- 8438 534- 92- 2910 Darby Andy 510 422- 3232 222 Juniper Ct. Concord CA USA 94519 5023 423- 42- 9933 534- 92- 2910 Askanzi Robert 510 422- 3232 222 Juniper Ct. Concord CA USA 94519 5023 838- 28- 1982 534- 92- 2910 Zavatta Virginia 510 423- 4932 629 Wind Way Concord CA USA 94521 5023 433- 43- 3838 534- 92- 2910 Fife Ben 510 322- 8427 782 Sapling Ct. Concord CA USA 94519 stor- _id emp- _id mgr- _id emp_- lname emp_- fname phone address city state coun -try postalcodeAPPENDIX B The pubs3 Database Transact-SQL User’s Guide 733 references titles(title_id), lorange int null, hirange int null, royalty int null) Its nonclustered index for the title_id column is defined as: create nonclustered index titleidind on roysched (title_id) Table B-9 lists the contents of roysched:Tables in the pubs3 database 734 Adaptive Server Enterprise Table B-9: roysched table title_id lorange hirange royalty BU1032 0 5000 10 BU1032 5001 50000 12 PC1035 0 2000 10 PC1035 2001 3000 12 PC1035 3001 4000 14 PC1035 4001 10000 16 PC1035 10001 50000 18 BU2075 0 1000 10 BU2075 1001 3000 12 BU2075 3001 5000 14 BU2075 5001 7000 16 BU2075 7001 10000 18 BU2075 10001 12000 20 BU2075 12001 14000 22 BU2075 14001 50000 24 PS2091 0 1000 10 PS2091 1001 5000 12 PS2091 5001 10000 14 PS2091 10001 50000 16 PS2106 0 2000 10 PS2106 2001 5000 12 PS2106 5001 10000 14 PS2106 10001 50000 16 MC3021 0 1000 10 MC3021 1001 2000 12 MC3021 2001 4000 14 MC3021 4001 6000 16 MC3021 6001 8000 18 MC3021 8001 10000 20 MC3021 10001 12000 22 MC3021 12001 50000 24 TC3218 0 2000 10 TC3218 2001 4000 12 TC3218 4001 6000 14 TC3218 6001 8000 16 TC3218 8001 10000 18APPENDIX B The pubs3 Database Transact-SQL User’s Guide 735 TC3218 10001 12000 20 TC3218 12001 14000 22 TC3218 14001 50000 24 PC8888 0 5000 10 PC8888 5001 10000 12 PC8888 10001 15000 14 PC8888 15001 50000 16 PS7777 0 5000 10 PS7777 5001 50000 12 PS3333 0 5000 10 PS3333 5001 10000 12 PS3333 10001 15000 14 PS3333 15001 50000 16 BU1111 0 4000 10 BU1111 4001 8000 12 BU1111 8001 10000 14 BU1111 12001 16000 16 BU1111 16001 20000 18 BU1111 20001 24000 20 BU1111 24001 28000 22 BU1111 28001 50000 24 MC2222 0 2000 10 MC2222 2001 4000 12 MC2222 4001 8000 14 MC2222 8001 12000 16 MC2222 8001 12000 16 MC2222 12001 20000 18 MC2222 20001 50000 20 TC7777 0 5000 10 TC7777 5001 15000 12 TC7777 15001 50000 14 TC4203 0 2000 10 TC4203 2001 8000 12 TC4203 8001 16000 14 TC4203 16001 24000 16 TC4203 24001 32000 18 TC4203 32001 40000 20 title_id lorange hirange royaltyTables in the pubs3 database 736 Adaptive Server Enterprise discounts table discounts is defined as follows: create table discounts (discounttype varchar(40) not null, stor_id char(4) null references stores(stor_id), lowqty smallint null, highqty smallint null, discount float not null) Table B-10 lists the contents of discounts: Table B-10: discounts table TC4203 40001 50000 22 BU7832 0 5000 10 BU7832 5001 10000 12 BU7832 10001 15000 14 BU7832 15001 20000 16 BU7832 20001 25000 18 BU7832 25001 30000 20 BU7832 30001 35000 22 BU7832 35001 50000 24 PS1372 0 10000 10 PS1372 10001 20000 12 PS1372 20001 30000 14 PS1372 30001 40000 16 PS1372 40001 50000 18 title_id lorange hirange royalty discounttype stor_id lowqty highqty discount Initial Customer 8042 NULL NULL 10.5 Volume Discount NULL 100 1001 6.7 Huge Volume Discount NULL 1001 NULL 10 Customer Discount 8042 NULL NULL 5APPENDIX B The pubs3 Database Transact-SQL User’s Guide 737 blurbs table blurbs is defined as follows: create table blurbs (au_id id not null references authors(au_id), copy text null) Table B-11 lists the contents of blurbs: Table B-11: blurbs table au_id copy 486-29-1786 If Chastity Locksley didn’t exist, this troubled world would have created her! Not only did she master the mystic secrets of inner strength to conquer adversity when she encountered it in life, but also, after “reinventing herself,” as she says, by writing “Emotional Security: A New Algorithm” following the devastating loss of her cat, Old Algorithm, she founded Publish or Perish, the page-by-page, day-by-day, write-yourself-to-wellness encounter workshops franchise empire, the better to share her inspiring discoveries with us all. Her “Net Etiquette,” a brilliant social treatise in its own right and a fabulous pun, is the only civilized alternative to the gross etiquette often practiced on the public networks. 648-92-1872 A chef’s chef and a raconteur’s raconteur, Reginald Blotchet-Halls calls London his second home. “Th’ palace kitchen’s me first ‘ome, act’lly!” Blotchet-Halls’ astounding ability to delight our palates with palace delights is matched only by his equal skill in satisfying our perpetual hunger for delicious back-stairs gossip by serving up tidbits and entrees literally fit for a king! 998-72-3567 Albert Ringer was born in a trunk to circus parents, but another kind of circus trunk played a more important role in his life years later. He grew up as an itinerant wrestler and roustabout in the renowned Ringer Brothers and Betty and Bernie’s Circus. Once known in the literary world only as Anne Ringer’s wrestling brother, he became a writer while recuperating from a nearfatal injury received during a charity benefit bout with a gorilla. “Slingshotting” himself from the ring ropes, Albert flew over the gorilla’s head and would have landed head first on the concrete. He was saved from certain death by Nana, an elephant he had befriended as a child, who caught him in her trunk. Nana held him so tightly that three ribs cracked and he turned blue from lack of oxygen. “I was delirious. I had an out-of-body experience! My whole life passed before me eyes. I promised myself ‘If I get through this, I’ll use my remaining time to share what I learned out there.’ I owe it all to Nana!”Tables in the pubs3 database 738 Adaptive Server Enterprise 899-46-2035 Anne Ringer ran away from the circus as a child. A university creative writing professor and her family took Anne in and raised her as one of their own. In this warm and television-less setting she learned to appreciate the great classics of literature. The stream of aspiring and accomplished writers that flowed constantly through the house confirmed her repudiation of the circus family she’d been born into: “Barbarians!” The steadily growing recognition of her literary work was, to her, vindication. When her brother’s brush with death brought them together after many years, she took advantage of life’s crazy chance thing and broke the wall of anger that she had constructed to separate them. Together they wrote, “Is Anger the Enemy?” an even greater blockbuster than her other collaborative work, with Michel DeFrance, “The Gourmet Microwave.” 672-71-3249 They asked me to write about myself and my book, so here goes: I started a restaurant called “de Gustibus” with two of my friends. We named it that because you really can’t discuss taste. We’re very popular with young business types because we’re young business types ourselves. Whenever we tried to go out to eat in a group we always got into these long tiresome negotiations: “I just ate Italian,” or “I ate Greek yesterday,” or “I NEVER eat anything that’s not organic!” Inefficient. Not what business needs today. So, it came to us that we needed a restaurant we could all go to every day and not eat the same thing twice in a row maybe for a year! We thought, “Hey, why make people choose one kind of restaurant over another, when what they really want is a different kind of food?” At de Gustibus you can eat Italian, Chinese, Japanese, Greek, Russian, Tasmanian, Iranian, and on and on all at the same time. You never have to choose. You can even mix and match! We just pooled our recipes, opened the doors, and never looked back. We’re a big hit, what can I say? My recipes in “Sushi, Anyone?” are used at de Gustibus. They satisfy crowds for us every day. They will work for you, too. Period! 409-56-7008 Bennet was the classic too-busy executive. After discovering computer databases, he now has the time to run several successful businesses and sit on three major corporate boards. Bennet also donates time to community service organizations. Miraculously, he also finds time to write and market executive-oriented, in-depth computer hardware and software reviews. “I’m hyperkinetic, so being dynamic and fast-moving is a piece of cake. But being organized isn’t easy for me or for anyone I know. There’s just one word for that: ‘databases!’ Databases can cure you or kill you. If you get the right one, you can be like me. If you get the wrong one, watch out. Read my book!” au_id copyAPPENDIX B The pubs3 Database Transact-SQL User’s Guide 739 Diagram of the pubs3 database Figure B-1: Diagram of the pubs3 databaseDiagram of the pubs3 database 740 Adaptive Server EnterpriseTransact-SQL User’s Guide 741 Symbols & (ampersand) “and” bitwise operator 15, 49 * (asterisk) multiplication operator 14, 49–53 for overlength numbers 384 pairs surrounding comments 476 select and 44 *= (asterisk equals) outer join operator 173, 204 */ (asterisk slash), comment keyword 476 @ (at sign) local variable name 478 procedure parameters and 496 rule arguments and 441 @@ (at signs), global variable name 483 \ (backslash) character string continuation with 19 ::= (BNF notation) in SQL statements xxv ^ (caret) “exclusive or” bitwise operator 15, 49 , (comma) in default print format for money values 215 in SQL statements xxv {} (curly braces) in SQL statements xxv $ (dollar sign) in identifiers 8 in money datatypes 322 -- (double hyphen) comments 28, 477 =* (equals asterisk) outer join operator 173, 204 = (equals sign) comparison operator 17, 60 > (greater than) comparison operator 17, 60 range specification 61 >= (greater than or equal to) comparison operator 17, 60 < (less than) comparing dates 60 comparison operator 17 range queries and 61 <= (less than or equal to) comparison operator 17, 60 - (minus sign) arithmetic operator 14, 49–53 for negative monetary values 322 != (not equal to) comparison operator 17, 60 <> (not equal to) comparison operator 17, 60 !> (not greater than) comparison operator 17, 60 !< (not less than) comparison operator 17, 60 () (parentheses) in arithmetic statements 52 in built-in functions 377 in expressions 13 in matching lists 63 in SQL statements xxiv in system functions 377 with union operators 116 % (percent sign) arithmetic operator (modulo) 14, 49–53 | (pipe) “or” bitwise operator 15, 49 + (plus) arithmetic operator 14, 49–53 null values and 76 string concatenation operator 16, 387 # (pound sign), temporary table identifier prefix 242, 251, 253 £ (pound sterling sign) in identifiers 8 in money datatypes 322 “ ” (quotation marks) comparison operators and 17 enclosing column headings 47–48 enclosing empty strings 18, 328 enclosing parameter values 499 enclosing passwords 33 enclosing values 216, 316–317 in expressions 18 IndexIndex 742 Adaptive Server Enterprise literal specification of 18 / (slash) arithmetic operator (division) 14, 49–53 /* (slash asterisk), comment keyword 476 [ ] (square brackets) in SQL statements xxv ~ (tilde) “not” bitwise operator 15, 49 _ (underscore) in temporary table names 252 ¥ (yen sign) in identifiers 8 in money datatypes 322 Numerics “0x” 322 counted in textsize 54 A abbreviations date parts 397 out for output 517 abs absolute value mathematical function 394 abstract plan derived tables differences from SQL derived tables 155 accounts, server. See logins; users acos mathematical function 394 adding column data with insert 326, 335–337 foreign keys 564–565 IDENTITY column to a table 293 rows to a table or view 324–337 timestamp column 619 user-defined datatypes 226–227 users to a database 234 addition operator (+) 14, 49–53 administrative instructions and results 2 aggregate functions 79–84, 392–393 See also row aggregates; individual function names compute clause and 21, 106–113 cursors and 601 datatypes and 81 distinct keyword and 80, 83 group by clause and 85–99 on multiple columns 112 nesting 92 null values and 84 order by clause and 104 scalar aggregates 81 subqueries including 132 vector aggregates 86 views and 364 where clause, not permitted 81 aliases table correlation names 58 all keyword comparison operators and 134, 144 group by 95–96 searching with 135 select 55–57 subqueries including 19, 136, 144 union 116 allow nested triggers configuration parameter 579– 581 allow_dup_row option, create index 426–427 alter database command 239–240 See also create database command alter table adding a column 285–287 adding columns with user-defined datatypes 297 adding columns, effect on column IDs 286 adding constraints 287 adding IDENTITY columns 293 adding not-null columns 286 and CIS 285 and dumping the transaction log 284 bulk copying existing dumps into modified columns 290 changing exp_row_size during data copy 296 command 283–300 converting datatypes 290 data copying 295–296 decreasing column length truncates data 290 dropping columns 287–289 dropping columns with user-defined datatypes 298 dropping columns, effect on column IDs 288 dropping constraints 289Index Transact-SQL User’s Guide 743 dropping IDENTITY columns 294–295 error messages 298–300 errors generated by alter table modify 299–300 exclusive table lock 284 execute immediate statement in 300 modifying columns 289–293 modifying columns with precision 292 modifying columns with scale 292 modifying columns with user-defined datatypes 298 modifying datetime columns 291 modifying locking scheme 297 modifying NULL default values 291–292 modifying text and image columns 292 objects that perform a select * 284 of table with a clustered index 297 on remote tables 285 restrictions for dropping IDENTITY columns 294–295 syntax 283 when it performs a data copy 296 with arithabort numeric_truncation turned on or off 292 alter table command adding timestamp column 619 altering. See Changing and (&) bitwise operator 15, 49 and keyword in expressions 20 in joins 175 in search conditions 77–78 angles, mathematical functions for 394 ansinull option, set 30 any keyword in expressions 19 searching with 134 subqueries using 137–139, 144 approximate numeric datatypes 215 arguments date functions 397 mathematical functions 393 string functions 379 system functions 374–377 text functions 389 arithabort option, set arith_overflow and 29, 408 mathematical functions and arith_overflow 408 mathematical functions and numeric_truncation 409 arithignore option, set arith_overflow and 30, 408 arithmetic errors 29, 408 arithmetic expressions 13, 47 not allowed with distinct 83 operator precedence in 52 arithmetic operations 80 mixed mode 224–226 arithmetic operators 49–51 as comparison operators 60 in expressions 14, 47 precedence of 52–53, 78 ascending order, asc keyword 103 ASCII characters ascii string function and 380, 387 ascii string function 380, 387 asin mathematical function 394 asterisk (*) multiplication operator 14, 49–53 overlength numbers 384 pairs surrounding comments 476 select and 44 in subqueries with exists 144 at sign (@) local variable name 478 procedure parameters and 496 rule arguments and 441 atan mathematical function 394 @@char_convert global variable 486, 487 @@cis_version global variable 489 @@client_csid global variable 487 @@client_csname global variable 487 @@connections global variable 488 @@cpu_busy global variable 488 @@error global variable 483 select into and 280 @@guestuserid global variable 489 @@identity global variable 249, 331, 483 @@idle global variable 488 @@invaliduserid global variable 489 @@io_busy global variable 488Index 744 Adaptive Server Enterprise @@isolation global variable 486, 647 @@langid global variable 487 @@language global variable 487 @@max_connections global variable 489 @@maxcharlen global variable 487 @@maxgroupid global variable 489 @@maxuserid global variable 489 @@mingroupid global variable 489 @@minsuid global variable 489 @@minuserid global variable 489 @@ncharsize global variable 487 @@nestlevel global variable nested procedures and 504 nested triggers and 579 @@options global variable 486 @@pack_received global variable 488 @@pack_sent global variable 488 @@packet_errors global variable 488 @@parallel_degree global variable 486 @@procid global variable 489 @@rowcount global variable 486 cursors and 607 triggers and 564 @@scan_parallel_degree global variable 486 @@servername global variable 489 @@spid global variable 489 @@sqlstatus global variable 484 @@textcolid global variable 490 @@textdbid global variable 490 @@textobjid global variable 490 @@textptr global variable 490 @@textsize global variable 53, 486, 490 @@textts global variable 490 @@thresh_hysteresis global variable 489 @@timeticks global variable 489 @@total_errors global variable 488 @@total_read global variable 488 @@total_write global variable 488 @@tranchained global variable 486 @@trancount global variable 484, 639 @@transtate global variable 484, 637, 639 @@version global variable 489 atn2 mathematical function 394 au_pix table, pubs2 database 702 author blurbs table pubs2 database 701 pubs3 database 737 authors table pubs2 database 678–680 pubs3 database 708–710 auto identity database option 250 identity in nonunique indexes and 421 automatic operations chained transaction mode 642 datatype conversion 223, 402 hidden IDENTITY columns 250 triggers 557 avg aggregate function 80, 392 See also aggregate functions as row aggregate 109 B backing up. See recovery backslash (\) for character string continuation 19 Backus Naur Form (BNF) notation xxiv, xxv base 10 logarithm function 394 base date 320, 396 base tables. See tables batch processing 447 control-of-flow language 21, 447–448, 453–477 errors in 451–452 go command 452 local variables and 469 rules for 448–451 submitting as files 452–453 bcp (bulk copy utility) IDENTITY columns and 334 begin transaction command 635 begin...end commands 466 between keyword 61–62 check constraint using 271 binary datatype 221 See also datatypes like and 65 binary datatypes 221–222 “0x” prefix 322 concatenating 379Index Transact-SQL User’s Guide 745 conversion 409 operations on 379–389 binary expressions concatenating 16, 387–388 binary representation of data for bitwise operations 14 binding defaults 436–438 rules 442–443 bit datatype 222 See also datatypes bitwise operators 14–16, 49 blanks character datatypes and 217 in comparisons 17, 60, 70 empty string evaluated as 18 like and 70 removing leading with ltrim function 381 removing trailing with rtrim function 381 blurbs table pubs2 database 701 pubs3 database 737 BNF notation in SQL statements xxiv, xxv Boolean (logical) expressions 13 select statements in 455 brackets. See square brackets [ ] branching 469 break command 467–469 browse mode 618–620 cursor declarations and 619 timestamp datatype and 223, 376 built-in functions 373–411 aggregate 392–393 conversion 402 date 396–402 image 389–392 mathematical 393–396 security 412–413 string 379–389 system 373–379 text 389–392 type conversion 402–407 views and 355 bytes @@maxcharlen limit 487 @@ncharsize average length 487 @@textsixe limit 486 composite index limit 419 datatype storage 212, 241 delimited identifier limit 9 for text and image data 490 hexidecimal digits and 322 identifier limit 7 length of expression (datalength function) 375 output string limit 472 print messages limit 470 quoted column limit 48 retrieved by readtext 54 subquery limit 124 temporary table name limit 7 C calculating dates 401 Cartesian product 174 cascading changes (triggers) 558, 565 case expressions 456–466 when\xc9 then keyword 460 coalesce 464 comparing values and nullif 465 data representation 457 determining datatype 460 division by zero avoidance 457 search conditions in 460 stored procedure example 498 value comparisons and 462 case sensitivity 8 in comparison expressions 17 in SQL xxvi ceiling mathematical function 394 chained option, set 642 chained transaction mode 28, 642 changing See also updating database size 239–240 default database 36 index names 302 object names 301–302 tables 283–302 view definitions 362 changing data.Index 746 Adaptive Server Enterprise See data modification char datatype 217 See also character data; datatypes char datatype entry rules 316 in expressions 18 like and 65 char string function 380 @@char_convert global variable 486, 487 char_length string function 380 character data 215 See also individual character datatype names avoiding “NULL” in 327 converting 404 entry rules 316 operations on 379–389 searching for 71 trailing blanks in 217 character datatypes 216 converting from multibyte to single-byte 404 converting numbers to 405 character expressions 13 character set 6 character sets conversion errors 9 iso_1 9 character strings 71 continuation with backslash (\) 19 empty 18 matching 65 select list using 48 specifying quotes within 18 truncation 29 characters number of 380 special 7 wildcard 66–71, 501 charindex string function 380, 383–384 check constraints 263, 271 checkpoint command 665 @@cis_version global variable 489 clauses 2 client cursors 597 host computer name 375 @@client_csid global variable 487 @@client_csname global variable 487 close command 610 close on endtran option, set 662 closing cursors 595 clustered constraint create index 424 create table 267 clustered indexes 423–425 See alsoindexes integrity constraints 267 number of total pages used 376 used_pgs system function and 376 coalesce keyword, case 464 codes soundex 381 col_length system function 374, 377 col_name system function 374 column length decreasing with alter table 290 column names 10 changing in views 353 finding 374 qualifying in subqueries 125 column pairs. See joins; keys column-level constraints 264 columns See also Database objects; select command access permissions on 304 adding data with insert 326, 335–337 adding with alter table 285–287 defaults for 266, 436–438 dropping columns with user-defined datatypes 298 dropping with alter table 287–289 gaps in IDENTITY values 261–262 group by and 91 IDENTITY 247–250 indexing more than one 419 initializing text 343 joins and 170, 173 length definition 247 length of 374 modifying columns with user-defined datatypes 298 modifying with alter table 289–293 null values and check constraints 272Index Transact-SQL User’s Guide 747 null values and default 245 order in insert statements 326, 335 order in select statements 45 qualifying names in subqueries 125 rules 441 rules conflict with definitions of 247, 443 system-generated 247 variable-length 246 comma (,) default print format for money values 215 in SQL statements xxv command terminator 36 commands 2 See also individual command names not allowed in user-defined transactions 634 comments ANSI style 28 double-hyphen style 477 in SQL statements 476–477 commit command 635 common keys See also foreign keys; joins; primary keys comparing values in expressions 17 for joins 173 null 73, 481 timestamp 376, 620 comparison operators 59–61 See also relational expressions correlated subqueries and 151–153 in expressions 16 modified, in subqueries 134, 135 null values and 73, 481 symbols 17, 60 unmodified, in subqueries 131–133 compatibility, data create default and 435 component Integration Services alter table command on remote tables 285 and update statistics command 431 automatic IDENTITY columns 250 connecting to a server 36 described 26 image datatype 222 joins 167 text datatype 220 transactions and 632 triggers 583 composite indexes 419 computations. See computed columns compute clause 106–113 different aggregates in same 112 grand totals 113 multiple columns and 110, 111 not allowed in cursors 596 row aggregates and 109–112 subgroups and 110 subtotals for grouped summaries 106 unionand 119 using more than one 111 computed columns 48–53, 365 insert 336 with null values 50 update 339 and views 354, 365 computing dates 401 concatenation 387–388 binary data 379 expressions 379 strings 379 using + operator 16, 387 using + operator, null values and 76 connections transactions and 664 @@connections global variable 488 consistency transactions and 632 constants in expressions 18, 47 constraints 233, 263 adding with alter table 287 check 263, 271 column-level 264 default 263 dropping with alter table 289 primary key 263, 267 referential integrity 263, 268 table-level 264 unique 263, 267 with NULL values 245 with rules 443Index 748 Adaptive Server Enterprise continuation lines, character string 19 continue command 467–469 control-break report 106 control-of-flow language 21, 23, 453–477 conventions See also syntax naming 6–13 Transact-SQL 6–13 Transact-SQL syntax xxiv used in the Reference Manual xxiv conversion between character sets 8–9 datatypes 247 degrees to radians 395 implicit 18, 223, 402 integer value to character value 380 lower to higher datatypes 18 lowercase to uppercase 382 radians to degrees 394 string concatenation 16 uppercase to lowercase 380 convert function 223, 403–411 concatenation and 16, 379, 388 date styles 410 explicit conversion with 392 length default 404 truncating values 404 copying data with insert...select 336 rows 337 tables with bcp 333 tables with select into 277 correlated subqueries 148–153 comparison operators in 151 correlation names and 150 exists and 144 having clause in 152 correlation names in joins (ANSI syntax) 187–188 self-joins 178 SQL derived tables and 158 subqueries using 125, 150 table names 58, 178 cos mathematical function 394 cot mathematical function 394 count aggregate function 80, 392 See also aggregate functions on columns with null values 84, 93 as row aggregate 109 count(*) aggregate function 79–80, 82, 109 See also aggregate functions on columns with null values 93 including null values 84 @@cpu_busy global variable 488 create database command 236–240 batches using 449 create default command 435–436 batches and 449 create procedure with 517 create index command 418–428 batches using 449 ignore_dup_key 420 create procedure command 494–495, 495–509, 550 See also stored procedures; extended stored procedures (ESPs) batches using 449 null values and 500 output keyword 513–517 rules for 517 with recompile option 503 create rule command 440 batches using 449 create procedure with 517 create schema command 270 create table command 241–244 batches using 449 composite indexes and 419 constraints and 263 in different database 254 example 244, 274 null types and 244 null values and 327 in stored procedures 518 user-defined datatypes and 228 create trigger command 559–561 batches using 449 create procedure with 517 displaying text of 588 create view command 352 batches using 449 create procedure with 517 syntax 352Index Transact-SQL User’s Guide 749 union prohibited in 119 creating databases 236–238 datatypes 226–228 defaults 435–436, 439 indexes 418–425 rules 440 stored procedures 509–517 tables 274–282 temporary tables 242, 250–252 triggers 559–561 CS_DATAFMT structure 540 CS_SERVERMSG structure 540 curly braces ({}) in SQL statements xxv currency symbols 322 current database changing 235 finding name 375 finding number 375 current date 399 current user suser_id system function 376 suser_name system function 376 user system function 376 cursor result set 591, 600 cursor rows option, set 606 cursors 591–618 buffering client rows 607 client 597 closing 610 deallocating 610 declaring 596–603 deleting rows 609 error message 582 621 error message 592 622 execute 597 fetching 604–607 fetching multiple rows 606 for browse and 619 Halloween problem 603 join column updates 621–627 language 597 locking and 615 name conflicts 599 nonunique indexes 600 number of rows fetched 607 opening 604 position 591 positioned deletes and 620 positioned updates and 620 read-only 601 scans 600 scope 598, 598–599 searched deletes and 620 searched updates and 620 server 597 status 605 stored procedures and 613 subqueries and 123 transactions and 662–663 unique indexes 600 updatable 601 updating rows 608 variables 605 curunreservedpgs system function 375 custom datatypes. See user-defined datatypes D data copying 295–296 when does alter table perform a data copy 296 data definition 524 data dependency. See dependencies, database object data dictionary. See system tables data integrity 23, 232, 440 See also data modification; referential integrity methods 263 data modification 2, 348 permissions 314 text and image with writetext 342–343 update 337–342 views and 364 data_pgs system function 375 database devices 237 database integrity. See data integrity; referential integrity database object owners names in stored procedures 518Index 750 Adaptive Server Enterprise database objects 231 See also individual object names access permissions for 304 dropping 449 ID number (object_id) 376 naming 7–11 renaming 301–302 restrictions for alter table 284 stored procedures and 518, 519 system procedures and 524 Database Owners adding users 234 transferring ownership 236 user ID number 1 374 Databases ownership 236 databases 234–240 See also database objects adding users 234 choosing 235 creating user 236–238 default 31 dropping 240 help on 305 ID number, db_id function 375 joins and design 169 name 236 number of server 236 optional 234 size 237, 239–240 system 234 use command 235 user 234 datalength system function 375, 378, 390 datatype conversions 402–407 automatic 223 binary and numeric data 407 bit information 410 case expressions 460 character information 404 column definitions and 247 date and time information 405 domain errors 409 hexadecimal-like information 409 image 410 money information 405 numeric information 405, 406 overflow errors 408 rounding during 405 scale errors 409 datatype precedence. See precedence datatypes 211–224 aggregate functions and 81 altering columns with user defined 297–298 approximate numeric 215 character 215 converting with alter table 290 create table and 241, 244, 419 creating 226–229 datetime values comparison 17 defaults and 228, 436–438 dropping columns with user defined 298 entry rules 214, 316–324 hierarchy 224–226 integer 214 joins and 173 length 227 local variables and 478 mixed, arithmetic operations on 14 modifying columns with user defined 298 money 215 rules and 228, 442–443 summary of 212–213 temporary tables and 252 unichar 218 union 114 views and 352 datatypes, custom. See user-defined datatypes date datatype entry format 317 date functions 396–402 date parts 318, 397–400 abbreviation names and values 397 dateadd function 397, 401 datedatatype 317 datediff function 397, 401 dateformat option, set 318–320, 321 datename function 321, 397–400 datepart function 321, 397–400 datesIndex Transact-SQL User’s Guide 751 See also time values acceptable range of 317 adding date parts 401 calculating 401 comparing 17, 60 current 399 display formats 216, 397 entry formats 216, 317–321, 397 entry rules 71 functions for 396–402 like and 321 searching for 71, 321 storage 396 datetime datatype 215, 317, 396 See also dates; timestamp datatype comparison of 17 concatenating 388 entry format 317, 397 like and 65 operations on 396 storage 396 day date part 398 dayofyear date part abbreviation and values 398 db_id system function 375 db_name system function 375 dbcc (Database Consistency Checker) stored procedures and 518 DB-Library programs set options for 24 transactions and 659 dd. See day date part deallocate cursor command 610 deallocating cursors 595, 610 debugging aids 23 decimal datatype 323 declare command 478 declare cursor command 596 declaring cursors 593, 596–603 local variables 478–482 parameters 496–497 default database 31 default database devices 237 default keyword 266 create database 237 default parameters in stored procedures 500 default settings databases 36 date display format 216 language 31, 318, 321 parameters for stored procedures 498–501 print format for money values 215 default values datatype length 217, 221 datatype precision 214 datatype scale 214 datatypes 227 defaults 23, 434–435 See also database objects binding 436–438 column 329 creating 435–436, 439 datatypes and 228, 436–438 dropping 440 insert statements and 326 naming 435 null values and 276, 439 unbinding 438 defining local variables 478–482 degrees mathematical function 394 delayed execution (waitfor) 474–475 delete command 343–345, 366 See also dropping cursors and 609 multitable views and 364 subqueries and 128 triggers and 561, 563, 565–566 views and 364 deleted table 563, 597 deleting cursor rows 609 cursors 594 rows 343–345 views 368 delimited identifiers 9 dependencies, database object 530–531 dependencies, display 371 dependent tables 565 dependent views 362 derived column list and SQL derived tables 159Index 752 Adaptive Server Enterprise in a derived table expression 159 derived table expression aggregate functions and 163 constant expressions and 162 correlated attributes and 165 correlated SQL derived tables and 159 creating a table from 164 defining a SQL derived table 155 derived column lists 159 differences from create view command 158 joins and 163 nesting 160 renaming columns 161 See also SQL derived tables 155 subqueries and 147, 160 syntax 157 union operator and 161 views and 165 derived tables SQL derived tables 155 descending order (desc keyword) 103 designing tables 274 detail tables 562 devices 237 See also sysdevices table diagram pubs2 database 705 pubs3 database 739 difference (with exists and not exists) 146–147 difference string function 380, 385 dirty reads 644 See also isolation levels discounts table pubs2 database 700 pubs3 database 736 disk crashes. See recovery distinct keyword aggregate functions and 80, 83 cursors and 601 expression subqueries using 133 order by and 105 row aggregates and 109 select 55–57 select, null values and 57 distribution pages 346 division operator (/) 14, 49–53 DLL (dynamic link library). See dynamic link libraries dollar sign ($) in identifiers 8 in money datatypes 322 double precision datatype 215 double precision datatype entry format 323 drop commands in batches 449 drop database command 240 drop default command 440 drop index command 428 drop procedure command 503, 520, 552 drop rule command 445 drop table command 302–303 drop trigger command 586 drop view command 368 dropping See also delete command; individual drop commands databases 240 defaults 440 indexes 428 objects 449 primary keys 565–566 procedures 520 rows from a table 343–345 rules 445 system tables 302–303 tables 302–303, 363 triggers 586 views 363, 368 dump, database 665 duplicate key errors, user transaction 659 duplicate rows indexes and 426 removing with union 116 dw. See weekday date part dy. See dayofyear date part dynamic dumps 665 dynamic Link Libraries building 547–549 for extended stored procedures 547–549Index Transact-SQL User’s Guide 753 sample definition file 549 search order 547 UNIX makefile 547 Windows NT makefile 549 E e or E exponent notation approximate numeric datatypes 323 money datatypes 322 else keyword. See if...else conditions embedding join operations 168 empty string (“ ”) or (’ ’) 217, 388 not evaluated as null 328 as a single space 18 encryption data 5 end keyword 461, 466 enhancements to SQL 20–26 equal to. See Comparison operators See comparison operators equijoins 172, 175 @@error global variable 483 select into and 280 error handling 23 error messages 12205 669, 670 12207 653, 668 582 621 592 622 constraints and 265 lock table command 653, 668 numbering of 472 set lock wait 669 severity levels of 473 user-defined transactions and 663 errorexit keyword, waitfor 475 errors arithmetic overflow 408 in batches 451–452 convert function 404–409 divide-by-zero 408 domain 409 duplicate key 659 packet 488 return status values 510–517 scale 409 trapping mathematical 395 triggers and 579 in user-defined transactions 659 escape characters 69 esp execution priority configuration parameter 538 esp unload dll configuration parameter 535, 538 ESPs. See extended stored procedures European characters in object identifiers 9 execute command 12, 495 for ESPs 552 output keyword 513–517 with recompile option 504 execute cursors 597 execution extended stored procedures 537 exists keyword 146–147, 455 search conditions 143 exp mathematical function 394 explicit null value 327 explicit transactions 643 explicit values for IDENTITY columns 331 exponential value 394 expression subqueries 131–133 expressions 60, 80 concatenating 379, 387–388 converting datatypes 402–407 definition of 13 including null values 76 replacing with subqueries 129 types of 13 extended stored procedures 22, 533–555 creating 550, 551 creating functions for 539–549 DLL support for 535 example 536 exceptions 555 executing 552 freeing memory of 538 function example 541 messages from 555 naming 536Index 754 Adaptive Server Enterprise Open Server support for 535 performance impact of 538–539 permissions on 537 priority of 538 removing 552 renaming 552 extensions, Transact-SQL 7, 25–26 F FALSE, return value of 143 fetch command 604 fetching cursors 594 fields, data. See Columns See columns files batch 452–453 finding object dependencies 302 FIPS flagger 27 fipsflagger option, set 27 fixed-length columns binary datatypes for 221 character datatypes for 217 compared to variable-length 217 null values in 246 float datatype 215 See also datatypes computing with 395 entry format 323 floating-point data 323 See also float datatype; real datatype floor mathematical function 394 flushmessage option, set 24 for browse option, select 119 not allowed in cursors 596 for load option alter database 239 create database 238 for read only option, declare cursor 596, 601 for update option, declare cursor 596, 601 foreign key constraint 269 foreign keys 562 inserting 564–565 sp_help report on 307 updating 572–573 format strings print 471 free pages, curunreservedpgs system function 375 from keyword 57 delete 344 joins 171 SQL derived tables 157 update 341 front-end applications, browse mode and 618 full name 31 functions 373–411 aggregate 392–393 conversion 402–411 date 396–402 image 389–392 mathematical 393–396 security 412–413 string 379–389 system 373–378 text 389–392 and views 355 futureonly option defaults 437, 438 rules 442, 445 G gaps in IDENTITY column values 254–262 getdate date function 397–399 global variables 483–490, 518 See also individual variable names go command terminator 36, 447 goto keyword 469 grand totals compute 113 order by 103 grant command 303 greater than. See Comparison operators See comparison operators group by clause 85–92, 601 aggregate functions and 85–99, 107 all and 95–96Index Transact-SQL User’s Guide 755 correlated subqueries compared to 151–152 having clause and 97–99 multiple columns in 91 nesting 87–92 null values and 93 order by and 104 select 87 subqueries using 133–134 triggers using 573–575 union and 119 where clause and 94–95 without aggregate functions 85, 91 grouping See also user-defined transactions procedures 658 procedures of the same name 503 groups database users 31 discretionary access control and 31 membership in 31 guest users 233, 234, 374 @@guestuserid global variable 489 H Halloween problem 603 having clause 97–102 different from where clause 97 group by and 97 logical operators and 98 subqueries using 133–134, 152 union and 119 without aggregates 98 without group by 101 headings, column 46–48 help reports See also individual system procedures columns 445 database devices 237 database object 305–307 databases 305 datatypes 305–307 defaults 445 dependencies 530 indexes 429 rules 445 system procedures 528 text, object 529 triggers 587 hexadecimal numbers “0x” prefix for 54, 322 converting 406 hextoint function 223, 410 hh. See hour date part hierarchy See also precedence datatype 224–226 operators 13 holdlock keyword 596, 632 cursors and 616 readtext 391 host computer name 375 host process ID, client process 375 host_id system function 375 host_name system function 375 hour date part 398 hyphens as comments 477 I identifiers 6–11 delimited 9 quoted 9 system functions and 377 IDENTITY columns 247–250 @@identity global variable 483 adding 293 and referential integrity 249 Component Integration Services 250 creating tables with 247 datatype of 248 deleting with syb_identity keyword 345 dropping 294–295 explicit values for 331 gaps in values 261–262, 333 gaps, eliminating 333 inserting values into 330, 368 nonunique indexes 420 renumbering 333Index 756 Adaptive Server Enterprise reserving block of 332 restrictions for dropping 294–295 selecting 250, 281 syb_identity in views 357 syb_identity keyword 250 unique values for 331 updating with syb_identity keyword 342 user-defined datatypes and 248 using with select into 280–282 views and 357–358, 368 @@identity global variable 249, 331, 483 identity grab size configuration parameter 332 identity in nonunique index database option 420, 600 identity keyword 248 IDENTITY property for user-defined datatypes 228 identity_insert option, set 331 @@idle global variable 488 IDs, user database (db_id) 375 server user 376 user_id function for 376 if update clause, create trigger 560, 583–584 if...else conditions 454–456, 467 case expressions compared to 456 ignore_dup_key option, create index 420, 426 ignore_dup_row option, create index 426–427 image datatype 221–222 See also datatypes ‘‘0x’’ prefix for 322 changing with writetext 342 Component Integration Services 222 initializing with null values 247 inserting 325 null values in 247 prohibited actions on 104 selecting 53–391 selecting in views 361 subqueries using 123 triggers and 583 union not allowed on 119 updating 338 writetext to 365 image functions 389 implicit conversion (of datatypes) 18, 223, 402 implicit transactions 642 in keyword 62–64 check constraint using 271 in expressions 19 subqueries using 138, 140–142 index pages allocation of 376 system functions 375, 376 total of table and 376 index_col system function 375 indexes See also clustered indexes; database objects composite 419 creating 418–425 distribution pages 346 dropping 428 duplicate values and 426 guidelines for 417–418 IDENTITY columns in nonunique 420 integrity constraints 267 joins and 417 key values 424 leaf level 423, 425 on multiple columns 419 naming 10 nonclustered 423–425 options 425–428 on presorted data 427–428 on primary keys 417, 423 renaming 302 retrieval speed and 417, 418, 424 searching 418 space used by 309 unique 420, 426 views and 352, 353 infected processes 475 information messages (Server). See error messages; severity levels inner joins 189–192 join table (ANSI syntax) 190 nested (ANSI syntax) 190 on clause (ANSI syntax) 191–192 inner queries. See Subqueries inner tables predicate restrictions (ANSI syntax) 196–197 input packets, number of 488 insert command 324–337, 366Index Transact-SQL User’s Guide 757 batches using 449 duplicate data from 426, 427 IDENTITY columns and 330 image data and 222 null/not null columns and 327, 328 rules and 434 select 325 subqueries and 128 text data and 220 triggers and 561, 563, 564–565 union operator in 119 views and 364 inserted table 563, 597 inserting rows 324–337 installing sample image data in pubs2 703 installmaster script 520 int datatype 324 See also integer data; smallint datatype; tinyint datatype integer data 214 See also individual datatype names converting 406 integer remainder. See modulo operator (%) integrity of data 232 constraints 263 transactions and 656 unique indexes 420 integrity. See dbcc (database consistency checker); referential integrity interactive SQL 453–477 internal structures pages used for 376 intersection (set operation) 146–147 into clause, select. See select into command into keyword fetch 605 insert 325 select 277 union 118 inttohex function 223, 410 @@invaliduserid global variable 489 @@io_busy global variable 488 is null keyword 75, 328 is_sec_service_on security function 412 isnull system function 75, 375, 378 insert and 328 iso_1 character set 9 @@isolation global variable 486, 647 isolation levels 28, 641, 644 changing for queries 647 cursor locking 649 defined 644 level 0 reads 420 readpast option and 672 transactions 641–647 isql utility command xx, 35–37 batch files for 452–453 go command terminator 36, 447 J Japanese character sets 217 object identifiers and 8 joined table 186 joins 4 column names in 173 column order in results 170 comparison operators 177 Component Integration Services 167 correlation names (ANSI syntax) 187–188 correlation names and 178 equijoins 172, 175 from clause in 171 help for 208 indexes and 417 inner joins (ANSI syntax) 186, 189–192 joined table 186 left join 184 many tables in 182–183 natural 175 not-equal 177, 179–182 null values and 73, 207 operators for 172, 173, 177 outer 173, 184–207 outer joins (ANSI syntax) 192–203 process of 168, 174 relational model and 169Index 758 Adaptive Server Enterprise relational operators and 172 restrictions 173 right join 184 select list in 169–171 selection criteria for 176 self-joins 178–179 self-joins compared to subqueries 126 subqueries compared to 141–142, 181 theta 173 updates using 341 used with views 185, 356 views and 355 where clause in 172, 174, 176 K key values 424 keys, table See also common keys; foreign keys; primary keys views and 352 keywords 6–7 control-of-flow 453–477 new 30 phrases 2 L labels 469 @@langid global variable 487 language cursors 597 language defaults 31, 318, 321 @@language global variable 487 language option, set 318, 321 languages, alternate effect on date parts 318, 321, 399 last-chance thresholds 376 lct_admin system function 376 leaf levels of indexes 423, 425 length of expressions in bytes 375 of columns 374 less than. See Comparison operators See comparison operators levels nested transactions 639 @@trancount global variable 484, 639 transaction isolation 641–647 like keyword 65–71 check constraint using 271 searching for dates with 321 lines (text), entering long 19 list, matching in select 62–64 listing database objects 309 datatypes with types 224–225 lists dbcc stored procedures 528 literal character specification quotes (“ ”) 18 literal values null 76 local and remote servers. See remote servers local variables 469–482 displaying on screen 470–472 last row assignment 479 printing values 479 SQL derived tables and 158 lock table command 652–653, 668 error message 12207 and 653, 668 lock timeouts set lock wait command 669 lock wait option, set command 669 lock wait period configuration parameter 669 locking cursors and 615 transactions and 632 log mathematical function 394 log on option create database 238 log10 mathematical function 394 logging out of isql 37 logical expressions case expression and 456 if...else 454 syntax 19 truth tables for 20 logical operators 77–78Index Transact-SQL User’s Guide 759 having clauses 98 login process 35–36 logins account information 32 logs. See transaction logs log10 mathematical function 394 loops break and 467 continue and 467 while 466–469 lower and higher datatypes. See precedence lower string function 380 ltrim string function 381 M macintosh character set 9 makefile for ESP DLLs 547–549 master database 234 guest user in 234 master tables 562 master-detail relationship 562 matching row (*= or =*), outer join 184 mathematical functions examples 395 list 394–395 syntax 393 max aggregate function 80, 392 See also aggregate functions as row aggregate 109 @@max_connections global variable 489 @@maxcharlen global variable 487 @@maxgroupid global variable 489 @@maxuserid global variable 489 messages 470–474 transactions and 663 mi. See minute date part millisecond date part 398 min aggregate function 80, 392 See also aggregate functions as row aggregate 109 @@mingroupid global variable 489 @@minsuid global variable 489 minus sign (-) subtraction operator 14 @@minuserid global variable 489 minute date part 398 mirrorexit keyword 475 mixed datatypes, arithmetic operations on 14, 224– 226 mm. See month date part model database 226, 234 user-defined datatypes in 252 modifying databases 239 tables 283 modifying data. See data modification modulo operator (%) 14, 49–53 money datatype 215, 225 money datatype See also smallmoney datatype entry format 322 monitoring system activity 487 month date part 398 month values date part abbreviation and 398 ms. See millisecond date part multibyte character sets converting 404 datatypes for 217 multicolumn index. See composite indexes multiple SQL statements. See batch processing multiplication (*) operator 14, 49–53 multitable views 186, 356, 367 delete and 185, 356 insert and 185, 356 N “N/A”, using “NULL” or 327Index 760 Adaptive Server Enterprise names alias for table 58 date parts 397 db_name function 375 host computer 375 index_col and index 375 object_name function 376 suser_name function 376 of transactions 637 user system function 376 user_name function 376 naming See also renaming columns 10 conventions 6–11 database objects 7–11 databases 236 indexes 10 labels 469 local variables 478 parameters in procedures 496–497 rules 441 savepoints 636 stored procedures 11–13 tables 242, 301–302 temporary tables 7, 242, 252 transactions 630, 635 triggers 560 views 11–13 natural joins 175 nchar datatype 217 entry rules 316 like and 65 operations on 379–389 @@ncharsize global variable 487 negative sign (-) in money values 322 nested queries. See nesting; subqueries nesting See also joins aggregate functions 92 begin transaction/commit statements 639 begin...end blocks 466 comments 476 group by clauses 87–92 groups 87 if...else conditions 456 levels 504 sorts 103 stored procedures 504 string functions 379, 388 subqueries 127 transactions 639, 654 triggers 504, 579–581 vector aggregates 92 warning on transactions 637 while loops 469 @@nestlevel global variable nested procedures and 504 nested triggers and 579 noholdlock keyword, select 649 nonclustered constraint create index 424 nonclustered indexes 423–425 integrity constraints 267 “none”, using “NULL” or 327 nonrepeatable reads 644 nonsharable temporary tables 251 normalization 169, 218 not between keyword 61 not exists keyword 146–147 See also exists keyword not in keyword 62–64 null values and 142 subqueries using 142–143 not keyword See also logical operators search conditions 61, 77–78 not like keyword 67 not null keyword 227, 245, 276 See also null values not null values 245 not-equal joins 179–182 compared to subqueries 142 null keyword 72, 266 See also Null values defaults and 244, 439 in user-defined datatypes 227 null string in character columns 327 null values 71–75, 244–245 aggregate functions and 84 built-in functions and 377Index Transact-SQL User’s Guide 761 case expressions and 460, 465–466 check constraints and 272 comparing 73, 481–482 comparing with nullif 465 in computed columns 50 constraints and 245 create procedure and 500 datatypes allowing 228 default parameters as 73 defaults and 276, 439 defining 245 distinct keyword and 57 group by and 93 insert and 329, 366 inserting substitute values for 328 joins and 74, 207 new rules and column definition 76 not allowed in IDENTITY columns 247 null defaults and 245 parameter defaults as 500, 502 rules and 245, 276 selecting 74–75 sort order of 103, 104 triggers and 583–584 variables and 478, 480, 481–482 nullif keyword 465 number (quantity of) databases within transactions 663 rows reported by rowcnt 376 server databases 236 tables allowed in a query 57, 171 number of pages allocated to table or index 376 reserved_pgs function 376 used by table and clustered index (total) 376 used by table or index 375 used_pgs function 376 numbers asterisks (**) for overlength 384 database ID 375 numeric data concatenating 388 operations on 395 numeric datatype 323 nvarchar datatype 217 See also character data; datatypes entry rules 316 like and 65 operations on 379–389 O object_id system function 376 object_name system function 376 objects. See database objects; individual object names of option, declare cursor 596 offset position, readtext command 391 on clause in outer joins (ANSI syntax) 195–199 of an inner join (ANSI syntax) 191–192 on an inner table (ANSI syntax) 197 on keyword alter database 239 create database 237 create index 419, 425, 428 create table 244 Open Client applications set options for 24 open command 604 opening cursors 594 operators arithmetic 14, 49–51, 52 bitwise 14–16, 49 comparison 16, 59–61 join 172 logical 77–78 precedence 13, 52, 78 relational 172 @@options global variable 486 or (|) bitwise operator 77–78 See also logical operators or keyword in expressions 20 in joins 175 order See alsoindexes; precedence; sort order of execution of operators in expressions 14 of null values 104 order by clause compute by and 109–110Index 762 Adaptive Server Enterprise group by and 104 indexing and 417 select and 103–104 union and 118 outer joins 184–207 See also joins ANSI syntax 193–194 converting outer joins with join-order dependency (ANSI syntax) 201–203 how predicates are evaluated in Transact-SQL outer joins 201 nested outer joins (ANSI syntax) 199–201 on clause (ANSI syntax) 195–199 on clause in nested outer join (ANSI syntax) 200–201 operators 173, 205–207 parentheses in nested outer joins (ANSI syntax) 200 placement of predicate (ANSI syntax) 195–199 position of the on clause in a nested outer join (ANSI syntax) 200–201 restrictions 185 restrictions for the where clause (ANSI syntax) 197– 199 roles of inner tables (ANSI syntax) 192 where clause (ANSI syntax) 195–199 outer tables predicate restrictions (ANSI syntax) 195–196 output option 513–517 overflow errors arithmetic 408 data and time conversion 405 set arithabort and 408 P @@pack_received global variable 488 @@pack_sent global variable 488 @@packet_errors global variable 488 padding, data null values and 247 underscores in temporary table names 252 pages, data allocation of 376 data_pgs system function 375 reserved_pgs system function 376 used for internal structures 376 used in a table or an index 375, 376 used_pgs system function 376 pair of columns. See common keys; joins @@parallel_degree global variable 486 parameters, procedure 496–502 delimited identifiers not allowed 9 maximum number 518 parameters, using defaults 500 parentheses () See also Symbols section of this index in arithmetic statements 52 in an expression 13 in SQL statements xxiv in system functions 377 passwords 35 changing 33 patindex string function 381 See also wildcard characters datatypes for 379 examples of using 383–384 text/image function 389 pattern matching 385 charindex string function 383 difference string function 385 patindex string function 383 percent sign (%) modulo operator 14, 49–53 performance indexes and 417 log placement and 238 stored procedures and 495 transactions and 633 triggers and 584 variable assignment and 478 period (.) separator for qualifier names 10 permissions 36, 233, 236 assigning 303 create procedure 495 data modification 314 database object owners 346 readtext and column 247 referential integrity 270 stored procedures 494, 519 system procedures 521–523Index Transact-SQL User’s Guide 763 triggers and 582, 587 views 354, 369 writetext and column 247 phantoms in transactions 644 pi mathematical function 394 placeholders print message 471 plus (+) arithmetic operator 14, 49–53 null values and 76 string concatenation operator 16, 387 pointers text or image column 342 positioning cursors 592 pound sign (#) temporary table name prefix 242, 251, 253 pound sterling sign (£) in identifiers 8 in money datatypes 322 power mathematical function 394 precedence of lower and higher datatypes 18 of operators in expressions 13 precision, datatype exact numeric types 323 predicate placement in outer join (ANSI syntax) 195–199 primary keys 307, 562 constraints 267 dropping 565–566 indexing on 417, 423 referential integrity and 562, 565 updating 567–571 print command 470–472, 473–474 privileges. See permissions proc_role system function 512 procedure calls, remote 34 procedures. See remote procedure calls; stored procedures; system procedures processes (Server tasks) infected 475 processexit keyword, waitfor 475 processing cursors 592 @@procid global variable 489 projection See also select command distinct views 357 queries 3 views 354 publishers table pubs2 database 677 pubs3 database 707 pubs2 database 37, 677–705 changing data in 315 diagram 705 guest user in 233 organization chart 705 table names 677 using in examples xx pubs3 database 37, 707–739 table names 707 punctuation enclosing in quotation marks 227 Q qq. See quarter date part qualifying column names in joins 170 column names in subqueries 125 database objects 10 object names within stored procedures 518 table names 242 quarter date part 398 queries 2, 3 nesting subqueries 127 optimizing 495 projection 3 query processing 492 quotation marks ( ) for empty strings 18 quotation marks (“ ”) comparison operators and 17 for empty strings 328 enclosing column headings 47–48 enclosing parameter values 499 enclosing values 216, 316–317 in expressions 18Index 764 Adaptive Server Enterprise literal specification of 18 quoted identifiers 9 R radians mathematical function 395 radians, conversion to degrees 394 raiserror command 472 rand mathematical function 395 range queries 61, 418 using < and > 61 read-only cursors 596, 601 readpast option 671–675 isolation levels and 672 readtext command 54 isolation levels and 647 and views 361 readtext command (advanced) 390–391 real datatype 215, 323 real datatype See also datatypes; numeric data records, table. See rows, table recovery 664–665 backing up databases 278 log placement and 238 temporary tables and 251 time and transaction size 663 transactions and 632 reference information datatypes 211 Transact-SQL functions 373 references constraint 269 referencing 530–531 referential integrity 268–271, 314 See also data integrity; triggers constraints 263, 268 create schema command 270 cross-referencing tables 270 general rules 270 IDENTITY columns 249 maximum references allowed 270 tips 272 triggers for 561–562 regulations batches 448 identifiers 6 relational expressions 19 See also comparison operators relational model, joins and 169 relational operations 3 relational operators 172 remarks text. See comments remote procedure calls 12–13, 34, 508–509 syntax for 493 user-defined transactions 659, 664 remote servers 12–13, 34, 508–509, 523 Component Integration Services 26 execute and 493 non-Sybase 26 system procedures affecting 522 removing. See dropping renaming See also naming database objects 301–302 stored procedures 519 tables 301–302, 363 views 363 repeating subquery. See subqueries replicate string function 381 repositioning cursors 595, 604 reserved_pgs system function 376 restoring sample databases 38 restrictions 3 See also select command results cursor result set 591 retrieving null values 73 retrieving data. See queries return command 470, 511 return parameters 513–517 return status 509–512 reverse string function 381 revoke command 303 right string function 381, 387Index Transact-SQL User’s Guide 765 right-justification of str function 384 roles show_role security function 412 stored procedures and 512 roles, user-defined 304 rollback command 635–636 See also transactions See also Transactions in stored procedures 663 triggers and 577, 663 rollback trigger command 577 round mathematical function 395 rounding approximate numeric datatypes 215 converting money values 405 datetime values 216 money values 215 str string function and 384 row aggregates 106 compared to aggregate functions 109 compute and 21, 109 group by clause and 110 views and 364 rowcnt system function 376 @@rowcount global variable 486 cursors and 607 triggers and 564 rows, table 3 See also triggers adding 324–337 changing 337–342 choosing 41, 58 copying 337 dropping 343–345 duplicate 116, 426–427 number of 376 summary 106–108 unique 427 roysched table pubs2 database 696–700 pubs3 database 732–736 RPCs (remote procedure calls). See remote procedure calls rtrim string function 381 rules 23, 327, 440 See also database objects binding 442–443 column definition conflict with 76 creating new 440 datatypes and 228 dropping user-defined 445 naming user-created 441 null values and 245 precedence 443 source text 444 specifying values with 441 testing 434, 440 triggers and 558 unbinding 444 and views 352, 353 violations in user transaction 659 with temporary constraints 443 S sales table pubs2 database 694 pubs3 database 725 salesdetail table pubs2 database 689–694 pubs3 database 719–725 sample databases. See pubs2 database; pubs3 database save transaction command 635–636 See also transactions See also Transactions savepoints 636 setting using save transaction 630 scalar aggregates 81, 92 @@scan_parallel_degree global variable 486 schemas 270 scope of cursors 598 screen messages 470–474 search conditions 58 second date part 398 security See also permissions stored procedures as 494, 519 views and 348, 369 security functions 412–413 seed values rand function 395Index 766 Adaptive Server Enterprise set identity_insert and 330 segments, placing objects on 244, 419, 425, 428 select * command 44–45, 171 limitations 336–337 new columns and limitations 504 select command 3, 41, 42–78 See also joins; subqueries; views Boolean expressions in 455 character data in 71 character strings in display 48 choosing columns 42 choosing rows 41, 58 column headings 46 column order in 45 combining results of 114–119 computing in 48–53 create view and 354 creating tables for results 277–279 database object names and 43 displaying results of 42, 45–48 with distinct 55–57 eliminating duplicate rows with 55–57 for browse 618 if...else keyword and 454 image data 53–391 inserting data with 325, 326, 334–337 isolation levels and 647 matching character strings with 65–71 quotation marks in 47–48 reserved words in 48 See also SQL derived tables 155 SQL derived tables 157 text data 53–391 variable assignment and 469–482 variable assignment and multiple row results 479 and views 364 wildcard characters in 66–69 select distinct query, group by and 105 select distinct query, order by and 105 select into command 277–279 compute and 109 IDENTITY columns and 281–282 not allowed in cursors 596 SQL derived tables 157 temporary table 254 union and 118 select into/bulkcopy/pllsort database option select into and 277 writetext and 342 select list 55, 169–171 subqueries using 144 union statements 114, 116 selections. See select command self-joins 178–179 compared to subqueries 126 server cursors 597 server user name and ID suser_id function 376 suser_name function for 376 @@servername global variable 489 servers executing remote procedures on 34 permissions for remote logins 34 set command chained transaction mode 28 character string truncation and 29 inside a stored procedure 506 transaction isolation levels and 645 within update 339 set theory operations 146–147 setuser command 236, 304 severity levels, error user-defined messages 473 shareable temporary tables 251 shared keyword cursors and 616 locking and 648 show_role system function 412 show_sec_services security function 413 sign mathematical function 395 sin mathematical function 395 size column 374 database 237, 239–240 size of columns, by datatype 212 slash (/) division operator 14, 49 slash asterisk (/*) comment keyword 476 smalldatetime datatype 215 See also datetime datatype; timestamp datatype converting 410Index Transact-SQL User’s Guide 767 date functions and 401–402 entry format 317, 397 operations on 396–401 storage of 397 smallint datatype 324 See also int datatype; tinyint datatype smallmoney datatype 215, 225 See also money datatype entry format 322 sort order See also order by clause comparison operators and 17 order by and 103 sorted_data option, create index 427–428 soundex string function 381, 385 source text 4 encrypting 5 sp_addextendedproc system procedure 551 sp_addmessage system procedure 473–474 sp_addtype system procedure 211, 227, 252 sp_bindefault system procedure 228, 436–438 batches using 449 sp_bindrule system procedure 228, 442–443 batches using 449 sp_changedbowner system procedure 236 sp_commonkey system procedure 209 sp_dboption system procedure transactions and 633 sp_depends system procedure 371, 530–531, 589 sp_displaylogin system procedure 32 sp_dropextendedproc system procedure 552 sp_dropsegment system procedure 240 sp_droptype system procedure 229 sp_extendsegment system procedure 240 sp_foreignkey system procedure 209, 307, 562 sp_freedll system procedure 535 sp_getmessage system procedure 473–474 sp_help system procedure 305–307 IDENTITY columns and 358 sp_helpconstraint system procedure 307 sp_helpdb system procedure 305 sp_helpdevice system procedure 237 sp_helpextendedproc system procedure 554 sp_helpindex system procedure 429 sp_helpjoins system procedure 208, 562 sp_helprotect system procedure 530 sp_helptext system procedure defaults 446 procedures 494, 529 rules 446 triggers 587, 588 sp_helpuser system procedure 31 sp_modifylogin system procedure 235 sp_monitor system procedure 487 sp_password system procedure 33 remote servers and 35 sp_primarykey system procedure 562 sp_procxmode system procedure 661 sp_recompile system procedure 495 sp_rename system procedure 301–302, 363, 519 sp_spaceused system procedure 309 sp_unbindefault system procedure 438 sp_unbindrule system procedure 444 space database storage 239–240 estimating table and index size 309 freeing with truncate table 346 for index pages 309 space string function 381 spaces, character empty strings (“ ”) or (’ ’) as 18, 328 special characters 7 speed (Server) of recovery 663 @@spid global variable 489 SQL derived tables advantages 156 aggregate functions and 163 and derived column lists 159 constant expressions and 162 correlated 159 correlated attributes and 165 correlation names and 158 creating tables from 164 defined by derived table expressions 155 differences from abstract plan derived tables 155 from keyword 157 joins and 163 local variables and 158 nesting 160 optimization and 157 renaming columns 161Index 768 Adaptive Server Enterprise See also derived table expression 155 select command 157 select into command 157 subqueries and 147, 160 subqueries with the union operator 161 syntax 157 temporary tables and 158 union operator and 161 using 160 using views with 165 SQL standards 26 set options for 24, 27 transactions 652 SQL. See Transact-SQL @@sqlstatus global variable 484, 605 sqrt mathematical function 395 square brackets [ ] in SQL statements xxv SRV_PROC structure 540 ss. See second date part statements 2, 6 statement blocks (begin...end) 466 timed execution of statement blocks 474 store_employees table, pubs3 database 727–732 stored procedures 21, 491–494 See also system procedures; triggers access permissions on 304 checking for roles in 512 compiling 492 control-of-flow language 453–477 creating 509–517 cursors within 613 default parameters 498–501 dependencies 530–531 dropping 520 grouping 503 information on 528 isolation levels 660 local variables and 478 modes 660 naming 11–13 nesting 504 object owner names in 518 parameters 496, 502 permissions on 494, 519 renaming 519 results display 493 return parameters 513–517 return status 509–512 rollback in 663 as security mechanisms 494, 519 source text 507 storage of 494 temporary tables and 252, 518 timed execution of 474 transactions and 654–662 with recompile 503 stores table pubs2 database 695 pubs3 database 726 str string function 381, 384 string functions 379–389 concatenating 387–388 examples 382–387 nesting 379, 388 testing similar 385 string_rtruncation option, set 29 strings concatenating 16, 379, 387–388 empty 217, 388 matching with like 65–71 truncating 316 Structured Query Language (SQL) 1 stuff string function 381, 384 subqueries 121 See also joins See also Joins aggregate functions and 132, 133 all keyword and 132, 136, 144 any keyword and 19, 132, 137, 144 column names in 125 comparison operators in 131–137, 144 comparison operators in correlated 151–153 correlated or repeating 148–153 correlation names in 125, 150 datatypes not allowed in 123 delete statements using 128 exists keyword in 143–147 in expressions 19 expressions, replacing with 129Index Transact-SQL User’s Guide 769 group by clause in 133–134, 151–152 having clause in 133–134, 152 in keyword and 63, 138, 140–142, 144 insert statements using 128 joins as 181 joins compared to 141–142 manipulating results in 123 modified comparison operators and 134, 135, 144 nesting 127 not exists keyword and 146–147 not in keyword and 142–143 not-equal joins and 181–182 null values and 122 order by and 104 repeating 148–153 restrictions on 123 select lists for 144 SQL derived tables and 147, 160 syntax 122–130 types 130 unmodified comparison operators and 131–133 update statements using 128 where clause and 123, 141, 143 substring string function 382 subtraction operator (-) 14, 49–53 suffix names, temporary table 252 sum aggregate function 80, 392 See also aggregate functions as row aggregate 109 summary rows 106–108 summary values 21, 79 aggregate functions and 106 triggers and 573–575 suser_id system function 376 suser_name system function 376 syb_identity keyword 250, 357 IDENTITY columns and 250, 330 sybsystemdb database 234 sybsystemprocs database 520, 554 symbols See also wildcard characters; Symbols section of this index arithmetic operator 14, 49 bitwise operator 49 comparison operator 17, 59, 60 matching character strings 66 money 322 in SQL statements xxiv synonyms datatype 212 keywords 30 out for output 517 syntax Transact-SQL 6–13 syntax conventions, Transact-SQL xxiv syscolumns table 222 syscomments table 494, 587 sysdatabases table 236 sysdevices table 237 syskeys table 209, 562 syslogs table 664 sysmessages table raiserror and 472 sysname custom datatype 223 sysobjects table 306–307 sysprocedures table 587 sysprocesses table 475 System Administrator database ownership 236 user ID 374 system datatypes. See datatypes system extended stored procedures 554 system functions examples 373, 377–378 syntax 373, 377 system procedures 22, 520–521 See also stored procedures; individual procedure names data definition 524 delimited identifiers not allowed as parameters 9 isolation level 651 for login management 522 not allowed in user-defined transactions 634 re-optimizing queries with 495 security administration 522 system administration 526 on temporary tables 254 viewing text of 530 system tables 233, 351 See also tables; individual table namesIndex 770 Adaptive Server Enterprise dropping 302–303 system procedures and 520 triggers and 582, 587–589 systypes table 224, 306, 307 sysusages table 236 sysusermessages table 473 sysusers table 233 T table columns. See columns table pages system functions 375, 376 table rows. See rows, table table-level constraints 264 tables 3, 240–254 See also database objects; triggers; views access permissions on 304 allowed in a from clause 57, 171 changing 283–302 correlation names 58, 125, 178 correlation names in subqueries 150 creating new 274–282 dependent 565 designing 274 dropping 302–303 IDENTITY column 247–248 inner 184 isnull system function and 328 joins of 167–209 names, in joins 171, 178 naming 7–11, 58, 242 outer 184 renaming 301–302 row copying in 337 space used by 309 tables, temporary. See temporary tables tan mathematical function 395 tempdb database 234 temporary tables 7, 58 See also tables; tempdb database create table and 242, 251–252 creating 250–252 naming 7, 242, 252 select into and 254, 277–279 SQL derived tables and 158 stored procedures and 518 triggers and 252, 582 views not permitted on 252, 352 text line continuation with backslash (\) 19 text datatype 220 See also datatypes changing with writetext 342 Component Integration Services 220 converting 404 entry rules 316 initializing with null values 247 inserting 325 length of data returned 24 like and 65, 67 operations on 379, 389–392 prohibited actions on 104 selecting 53–391 selecting in views 361 subqueries using 123 triggers and 583 union not allowed on 119 updating 338 updating in views 365 where clause and 59, 67 text functions 389–392 text pointer values 342 @@textcolid global variable 490 @@textdbid global variable 490 @@textobjid global variable 490 textptr function 390, 391 @@textptr global variable 490 @@textsize global variable 53, 486, 490 textsize option, set 390 @@textts global variable 490 textvalid function 390 The 26 theta joins 173 See alsojoins @@thresh_hysteresis global variable 489 thresholds last-chance 376Index Transact-SQL User’s Guide 771 time datatype 317 entry format 317 time interval, execution 475 time option, waitfor 474 time values See also dates; datetime datatype; smalldatetime datatype display format 397 entry format 317–318 functions on 396–399 like and 321 searching for 321 storage 396 timestamp datatype 223 See also datetime datatype; smalldatetime datatype browse mode and 618 comparing timestamp values 620 comparison using tsequal function 376 inserting data and 324 skipping 326 timestamp tsequal function 620 @@timeticks global variable 489 timing @@error status check 483 tinyint datatype 324 See also int datatype; smallint datatype titleauthor table pubs2 database 687–689 pubs3 database 717 titles table pubs2 database 680–687 pubs3 database 710–717 to_unichar string function 382 @@total_errors global variable 488 @@total_read global variable 488 @@total_write global variable 488 totals See also aggregate functions grand (compute without by) 113 with compute clause 106 @@tranchained global variable 486 @@trancount global variable 484, 639 transaction isolation levels readpast option and 672 transaction logs 664 on a separate device 238 size 238 writetext and 342 transactions 315, 629–665 canceling 663 Component Integration Services 632 cursors and 662 isolation levels 28, 641 locking 632 modes 28, 641 names not used in nested 637 naming 635 nesting levels 639, 654 number of databases allowed 663 performance and 633 recovery and 632, 664 SQL standards compliance 652 states 637 stored procedures and 636 stored procedures and triggers 654 timed execution 474 @@transtate global variable 637 triggers and 577, 636 Transact-SQL enhancements to 20–26 extensions 25–26 translation of integer arguments into binary numbers 15 @@transtate global variable 484 transtate global variable 637–639 trigger tables 560, 563 dropping 586 triggers 23, 557–589 See also database objects; stored procedures Component Integration Services 583 creating 559–561 dropping 586 help on 587 on image columns 583 naming 560 nested 579–581 nested, and rollback trigger 578 null values and 583–584 object renaming and 585 performance and 584 permissions and 582, 587 recursion 580Index 772 Adaptive Server Enterprise restrictions on 561, 582 rollback in 663 rolling back 577 rules and 558 self-recursion 580 set commands in 584 storage 587 summary values and 573–575 system tables and 582, 587–589 temporary tables and 582 test tables 562–564 on text columns 583 transactions and 577, 654–662 truncate table command and 582 views and 352, 353, 582 trigonometric functions 394 TRUE, return value of 143 truncate table command 346 referential integrity and 271 triggers and 582 truncation binary datatypes 322 character string 29 str conversion and 384 temporary table names 252 truth tables logical expressions 20 tsequal system function 376, 620 U uhighsurr string function 382 ulowsurr string function 382 unbinding defaults 438 rules 444 unchained transaction mode 642 underscore (_) in temporary table names 252 Unichar data 218 unichar datatype 217–218 like and 65 operations on 379–389 union operator 114–119, 601 unique constraints 263, 267 unique indexes 420, 426 unique keyword 420 duplicate data from 426 univarchar datatype like and 65 operations on 379–389 unknown values. See null values updatable cursors 601 update command 337–342, 366 cursors and 608 duplicate data from 426, 427 image data and 222 multitable views 364 null values and 245, 247, 329 rules and 434 subqueries using 128 text data and 220 triggers and 563, 567–573, 583 views and 186, 356, 364 update partition statistics command 432 update statistics command 431 with Component Integration Services 431 updating See also changing; data modification in browse mode 376, 618 cursor rows 608 cursors 594 foreign keys 572–573 image datatype 338 index statistics 431 partition statistics 432 prevention during browse mode 376 primary keys 567–571 text datatype 338 using join operations 341 upper string function 382, 387 uscalar string function 382 use command 235 batches using 448 create procedure with 517 used_pgs system function 376 user databases 234 user IDs 374 user_id function for 376 valid_user function 377Index Transact-SQL User’s Guide 773 user keyword create table 266 system function 376 user names defined 376 finding 376 user system function 376 user_id system function 376 user_name system function 374, 376, 378 user-defined datatypes 226–227 altering columns 297 defaults and 245, 436–438 dropping a column with 298 IDENTITY columns and 228, 248 modifying columns with 298 rules and 227–228, 442–443 sysname as 223 temporary tables and 254 timestamp as 223 user-defined procedures 491–531 user-defined roles 304 user-defined transactions. See transactions users adding 234 management 522 using option, readtext 391 V valid_name system function 377 checking strings with 8 valid_user system function 377 values IDENTITY columns 247 null 244 values option, insert 325 varbinary datatype 221 See also binary data; datatypes ‘‘0x’’ prefix 322 like and 65 operations on 379–389 varchar datatype 217 See also character data; datatypes entry rules 316 in expressions 18 like and 65 operations on 379–389 variable-length columns compared to fixed-length 217 null values in 246 variables comparing 481–482 declaring 478–482 global 483–490, 518 in update statements 340 last row assignment 479 local 469–482, 518 printing values 479 vector aggregates 86 nesting 92 @@version global variable 489 views 347, 351 See also database objects access permissions on 304 advantages 348 aggregate functions and 364 allowed in a from clause 57, 171 column names 352 computed columns and 365 creating 351 data modification and 364 datatypes and 352 defaults and 352, 353 dependent 362 distinct and 353 dropping 368 functions and 355 help on 369 IDENTITY columns and 368 indexes and 352, 353 insert and 359–360 joins and 167, 355 keys and 352 naming 10–11 permissions on 354, 369 projection of distinct 357 projections 354 querying 360 readtext and 361 redefining 362Index 774 Adaptive Server Enterprise references 371 renaming 363 renaming columns 353 resolution 360, 361 restrictions 364–368 retrieving data through 360 rules and 352, 353 security and 348 source text 358 temporary tables and 252, 352, 353 triggers and 252, 352, 353, 582 union and 119 update and 359–360 updates not allowed 365 using SQL derived tables with 165 with check option 185, 356, 359–360, 364, 367 with joins 185, 356 and writetext 361 W waitfor command 474–475 week date part 398 weekday date part 398 when...then conditions in case expressions 456, 460 where clause aggregate functions not permitted in 81 compared to having 97 group by clause and 94–95 in outer join (ANSI syntax) 195–199 join and 176 joins and 172 like and 67 null values in a 73 search conditions in 58 skeleton table creation with 279 subqueries using 123, 141, 143 text data and 59, 67 update 340 where current of clause 608, 609 while keyword 466–469 wildcard characters default parameters using 501 in a like match string 66–71 searching for 68 with check option option views and 359–360 with log option, writetext 315 with recompile option create procedure 503 execute 504 wk. See week date part work keyword (transactions) 635 write-ahead log 664 writetext command 342 and views 361, 365 with log option 315 X XP Server 22, 534–535, 556 xp_cmdshell context configuration parameter 538 xp_cmdshell system extended stored procedure 554 xp_cmdshell context configuration parameter and 538 xpserver utility command 556 Y year date part 398 yen sign (¥ ) in identifiers 8 in money datatypes 322 yy. See year date part Z zeros using NULL or 328