MCSE TestPrep SQL Server 6.5 Design & Implementation - 3- Data Definition

Transcription

1 MCSE TestPrep SQL Server 6.5 Design & Impementation - Data Definition Page 1 of 38 [Figures are not incuded in this sampe chapter] MCSE TestPrep SQL Server 6.5 Design & Impementation - 3- Data Definition This chapter heps you prepare for the exam by covering the foowing test objectives: Increasing transaction og size (covered in Section 3.1) Creating and modifying tabes (covered in section 3.4) Appying an IDENTITY property to a tabe definition (covered in Section 3.5) Identifying appropriate uses for the different types of constraints (covered in Section 3.5) Appying REFERENCE constraints to enforce referentia integrity (covered in Section 3.5) NOTE: The test objectives for this chapter are somewhat miseading. To best prepare for the exam, be sure you are famiiar with a the concepts discussed in this chapter. In addition, make sure you know the Transact-SQL commands used to manage databases and tabes. Athough Enterprise Manager can be used to manage databases and tabes, the test focuses on the SQL commands. 3.1 Understanding Databases and Transaction Logs In SQL Server, the database is at the top of the hierarchy of physica storage. Databases reside on one or more devices, which may reside on mutipe physica disks. Databases in SQL Server are composed of different segments, or database fragments. A segment is used to partition the information stored in a database, and may share a device with other segments. A database in SQL Server initiay consists of three segments: the system segment, the defaut (or data) segment, and the og segment. As the name impies, the system segment is where the database s system tabes (the database cataog) are stored. The defaut (or data) segment is where a the database s information is actuay stored; tabes, indexes, and other objects are created on the defaut segment. The og segment stores the database s transaction og. SQL Server uses the transaction og to record a changes made to a database Understanding the Transaction Log fie://i:\chapters\z\zc817.htm 3/21/01

2 MCSE TestPrep SQL Server 6.5 Design & Impementation - Data Definition Page 2 of 38 The transaction og is the heart of SQL Server s capabiity to recover a database in the event of a system crash. SQL Server uses a write-ahead og, which means that database changes are ogged before they are appied. If the server fais because of a power outage or other probem, SQL Server automaticay recovers the database by appying committed transactions and roing back incompete transactions. Here is a step-by-step overview of how SQL Server uses the transaction og: 1. Some sort of change to the database is made. Except for a few cases, every modification to a database is ogged. Some exampes of ogged modifications foow: Direct changes to the data caused by the execution of an INSERT, UPDATE, or DELETE statement Creation of a database object Page and extent aocations caused when information is added to a tabe or index NOTE: Non-ogged operations operate significanty faster than ogged operations because SQL Server does not have the additiona overhead of writing og records. Bukcopy and SELECT INTO operations can be non-ogged, and are usuay used for handing arge amounts of data. Non-ogged operations make the transaction og useess for database recovery, so the database shoud be fuy backed up after performing a non-ogged operation. 2. The pages to be modified are oaded into memory from disk. 3. As each modification is made, the change is written to the transaction og before the change is appied to the data. Transaction og changes are written immediatey to disk, but modified data pages are simpy modified in memory. 4. About once each minute, the SQL Server CHECKPOINT process ooks at the database and fushes any modified pages in memory to the disk. The CHECKPOINT marks the transaction og to indicate which transaction was ast written to disk. In the event of a system faiure, SQL Server performs automatic recovery on startup. SQL Server ooks at the transactions in the transaction og after the ast CHECKPOINT because these are database changes that have not been written to disk. Competed transactions are appied to the database (roed forward), and incompete transactions are backed out (roed back). For this recovery process to work, SQL Server must accuratey know when og changes have been written to disk. Disk controers that perform write caching can destroy the usefuness of the transaction og by making SQL Server beieve that og changes have been written to disk when they have not. In this situation, SQL Server s copy of the og and the copy of the og on disk are out of sync, and automatic recovery may fai. Because write caching amost aways improves disk performance, many high-performance servers have write-caching controers. Most of the better controers have a battery backup that maintains the cache in the event of a power faiure. Using write-caching controers with a battery backup is acceptabe because cached information can be written to disk on startup, and the SQL Server og remains intact. If your server has a write-caching controer, make sure it aso has a battery backup. fie://i:\chapters\z\zc817.htm 3/21/01

3 MCSE TestPrep SQL Server 6.5 Design & Impementation - Data Definition Page 3 of 38 Write-caching software cannot guarantee that cached information wi be written to disk in the event of a system faiure. Therefore, you shoud never use write-caching software with SQL Server Pacement of the Transaction Log The transaction og shoud be paced on a separate device from the rest of the database. Doing so provides the foowing benefits: The transaction og size may be expicity defined, and the og does not compete with the data for storage space. The size of the transaction og may be monitored by using a performance monitor or the DBCC command. The transaction og may be backed up independenty of the database, which increases the speed of backups and makes incrementa backups of the database possibe. Voatie databases may have their transaction ogs dumped severa times a day to provide up-to-the-minute recovery. Pacing the database and transaction og on separate physica disks can greaty improve the performance of SQL Server because data and og writes do not compete for disk time Practice Probems 1. How many segments exist in a new database? A. Four B. One C. Five D. Three 2. The purpose of the transaction og is to do which of the foowing? A. Audit users changes to the database B. Ensure the integrity of the database in the event of a system faiure C. Improve the performance of database changes D. Keep track of changes made to the database so incompete changes may be roed back E. Ensure up-to-the-minute database recoverabiity 3. SQL Server uses what kind of transaction og? A. Read-ahead B. Write-ahead C. Fai-safe D. Write-cached 4. Which database option enabes non-ogged operations to occur? A. seect into / bukcopy B. IDENTITY_INSERT C. noog D. CHECKPOINT 5. Pacing the transaction og on a device separate from the data device(s) provides which of the foowing benefits? (Seect a that appy.) A. Log size may be monitored. fie://i:\chapters\z\zc817.htm 3/21/01

4 MCSE TestPrep SQL Server 6.5 Design & Impementation - Data Definition Page 4 of 38 B. Incrementa backups of the database may be created. C. Performance of ogged operations may be improved. D. Non-ogged operations are aowed. E. The transaction og does not compete with data for storage space. 6. How does SQL Server recover from a server faiure? A. Re-oading the affected database objects from the defaut dump device B. Re-oading the entire database from the defaut dump device C. Appying committed transactions and roing back incompete transactions D. SQL Server has no buit-in recovery mechanisms, so it reies on the operating system to provide those services 7. Why are non-ogged operations on SQL Server faster than ogged operations? A. The og is on a different segment than the database data. B. The system overhead invoved in writing og fies is not incurred. C. The og device is separate from the data device. D. They are cached in memory by SQL server. 8. What precautionary steps shoud be taken to protect your data when performing non-ogged operations? A. The database shoud be fuy backed up after performing non-ogged operations. B. Ony the affected database objects shoud be backed up to reduce backup time. C. None; SQL Server automaticay backs up the database after non- ogged operations. D. None; the operating system auto- maticay schedues a backup when non-ogged operations are performed. 9. When changes are made to a database, when is the transaction og updated? A. After the data is modified B. Before the data pages are oaded into memory C. After the data pages are oaded into memory D. Before the data is modified in memory 10. When are transaction og changes written to the disk? A. When the server has determined that the data was successfuy updated. B. After the data is modified in memory. C. Changes are written immediatey to the disk. D. Changes are cached unti the cache is fu and are then fushed to the disk Answers and Expanations: Practice Probems 1. D Three segments originay exist on a new database. 2. B, D, E The primary purpose of the transaction og is to ensure the integrity of the database in the event of a system faiure. 3. B SQL Server uses a write-ahead transaction og. 4. A The seect into / bukcopy option enabes non-ogged operations to occur. 5. A, B, C, E Performance of ogged operations is improved and the transaction og does not compete with data for storage space if it is on a different device than the data. 6. C SQL Server recovers a database by appying committed transactions and roing back incompete transactions. fie://i:\chapters\z\zc817.htm 3/21/01

5 MCSE TestPrep SQL Server 6.5 Design & Impementation - Data Definition Page 5 of B Non-ogged operations are faster because the system overhead invoved in writing og fies is not incurred. 8. A The database shoud be fuy backed up after performing non-ogged operations. 9. D The transaction og is modified before the data is modified in memory. 10. C SQL Server writes transaction og changes immediatey to the disk Keywords Database fragments Transaction og Write-ahead og Logged operations Non-ogged operations 3.2 Managing Databases For the test, you need to know the various commands used to manage databases in SQL Server. This section covers the creation and deetion of databases, as we as the commands used to change the size of a database. In addition, you earn about the various configuration options avaiabe for a database. As noted, the test focuses mainy on the Transact-SQL commands used to manage databases Creating a Database Before impementing a data mode in SQL Server, you must create a database to store the various tabes and other objects required to store the information. By defaut, ony the system administrator can create databases, athough this permission may be transferred to other users. When you create a database, you give it a name, define on which device(s) it wi reside, and specify the size for the data and og. The CREATE DATABASE command is used to create a database using Transact-SQL. The syntax for the CREATE DATABASE command is as foows: CREATE DATABASE database_name [ON {DEFAULT database_device} [=size] [, database_device [=size]]...] [LOG ON {DEFAULT database_device} [=size] [, database_device [=size]]...] [FOR LOAD] The syntax is defined as foows: The ON keyword specifies on which device(s) the database is created. If this is omitted, the database is created on the defaut device(s). If a device is specified, but no size is specified, 2MB is aocated on that device. fie://i:\chapters\z\zc817.htm 3/21/01

6 MCSE TestPrep SQL Server 6.5 Design & Impementation - Data Definition Page 6 of 38 The LOG ON keyword specifies on which device(s) the og is created. If this is omitted, the og is shared with the data on the data device(s). When specifying the size of the database on a device, express the size in megabytes. Note that this is different than creating a device, where you specify the device size in number of 2KBpages. Use the FOR LOAD keyword if you intend to immediatey oad the database from a backup dump. Doing so prevents any users from accessing the database unti the oad is compete. In addition, no data pages in the database are initiaized, so creating the database takes much ess time. Note that SQL Server enabes you to create databases on removabe media, such as a foppy disk, CD-ROM, or ZIP drive. This feature is most usefu for distributing read-ony databases on CD-ROM. To create a database of this type, use the sp_create_removabe system stored procedure Changing the Size of a Database Databases in SQL Server may be resized if they are too sma or too arge. Databases are resized in.5mb increments, just as they are when they are created. Both resizing commands are fuy ogged, so it is possibe for the database to be recovered in the event of a system faiure. Nevertheess, it is a good idea to back up both the Master database and the database being resized before and after it is resized. Take specia care not to resize a database more than necessary. Resizing a database affects its recoverabiity in the event of a Master database corruption. Every time a database is resized, the database s structure is changed and the changes are recorded in Master. If the Master database is ost or corrupted, and no backup is avaiabe, the user databases must be re-created. For the backup dumps to work propery, user databases must be created at their origina size and changes must be appied in the correct order. The SQL Server 6.5 system stored procedure, sp_hep_revdatabase, creates a script that can propery re-create a database in the event of a Master database faiure. Another stored procedure, sp_coaesce_fragments, can reduce the number of database fragments created by mutipe resizings. Expanding a Database A database may be expanded by using the Transact-SQL ALTER DATABASE command or by using Enterprise Manager. Permissions to expand a database are transferred aong with permissions to create a database (these permissions defaut to the system administrator ony). The minimum expansion for a database is 1MB, and the expansion is 1MB. Aso, you must be in the Master database to expand a database. The syntax for the ALTER DATABASE command is as foows: ALTER DATABASE <database_name> [ON {DEFAULT database_device} [=size] [, database_device [=size]]...] [FOR LOAD] fie://i:\chapters\z\zc817.htm 3/21/01

7 MCSE TestPrep SQL Server 6.5 Design & Impementation - Data Definition Page 7 of 38 The same defauts appy for this command as for the CREATE DATABASE command. The syntax is expained as foows: The ON keyword specifies upon which device(s) the database wi be expanded. The size parameter is the size by which the database shoud be expanded, expressed in megabytes. Use the FOR LOAD keyword if you intend to immediatey oad the database from a backup dump. Shrinking a Database A database may be shrunk by using the Transact-SQL Database Consistency Checker (DBCC) SHRINKDB command or by using Enterprise Manager. Ony the system administrator or database owner (DBO) can shrink a database. When a database is shrunk, the data and og are both shrunk to bring the database to the specified size. Before a database can be shrunk, it must be paced in singeuser mode. Setting this database option is discussed ater in the chapter. You must execute the SHRINKDB command from the database to be shrunk. The database must be in singe-user mode before executing the SHRINKDB command. Use sp_dboption or Enterprise Manager to set this option. The syntax of the SHRINKDB command foows: DBCC SHRINKDB (database_name [,new_size]) This syntax is expained as foows: The database_name is the name of the database to shrink. The new_size parameter is the new size for the database, expressed in the number of 2KB pages. If this parameter is omitted, DBCC reports the minimum size to which the database may be shrunk. Note that the database may not be shrunk past the size of the Mode database or the defaut size for a database Deeting a Database Deeting (or dropping) a database competey removes the database from the server. A data in the database is deeted. However, the devices used by the database remain intact. To drop a database, use the Transact-SQL DROP DATABASE command. To drop a database, you must execute the command from the Master database. The syntax of the DROP DATABASE command is: DROP DATABASE <dbname> Database Options Each database has a number of configuration options specific to that database. Ony the system administrator or DBO can set these options, which foow: fie://i:\chapters\z\zc817.htm 3/21/01

8 MCSE TestPrep SQL Server 6.5 Design & Impementation - Data Definition Page 8 of 38 ANSI nu defaut: Specifies whether coumns are NULLabe by defaut. If this option is turned on, coumns that do not have their NULL option expicity defined during a CREATE TABLE or ALTER TABLE statement defaut to enabing NULLs. DBO use ony: If this option is turned on, ony the database owner (DBO) or users aiased to the DBO may access the database. no chkpt on recovery: Determines whether a checkpoint record is added to the og after autorecovery is performed at startup. offine: Primariy used for databases stored on removabe media. When a database is offine, no users can access the database. SQL Server does not open the fies containing the database s devices, and the database is not automaticay recovered at server startup. This option can be set ony by using sp_dboption. pubished: Determines whether a database is enabed to provide pubications for repication. This option can be set ony by using sp_dboption, and is usuay set ony when repication is set up on a server. read ony: If this option is turned on, users (incuding the system administrator and DBO) cannot modify any data in the database. seect into/bukcopy: If this option is turned on, non-ogged operations are permitted in the database. singe user: Turning this option on restricts the number of connections into the database. Ony one user may access the database at a time. This option is used with the DBCC SHRINKDB command described previousy. subscribed: Determines whether a database is enabed to subscribe to pubications from other databases invoved in repication. This option can be set ony by using sp_dboption, and is usuay set when repication is set up on a server. trunc. og on chkpt.: If set, committed transactions are removed from the transaction og every time the CHECKPOINT process occurs. This option is usefu in databases where transaction og dumps are not needed, such as a database under deveopment, because it reduces the ikeihood of the transaction og fiing up. Setting a database option in the Mode database causes that option to be set in a newy created databases. Database options can be set by using the sp_dboption system stored procedure, or through Enterprise Manager. A few of the options can be set ony by using sp_dboption. The syntax of the sp_dboption stored procedure is: sp_dboption [dbname] [, optname [, {TRUE FALSE } ]] sp_dboption behaves differenty when different options are specified. Consider the foowing exampes: fie://i:\chapters\z\zc817.htm 3/21/01

9 MCSE TestPrep SQL Server 6.5 Design & Impementation - Data Definition Page 9 of 38 Caing sp_dboption without any parameters causes a database options to be isted: sp_dboption Caing sp_dboption with ony a database name returns a ist of a enabed options in that database: sp_dboption pubs Caing sp_dboption with a database name and option name returns the current setting for that option: sp_dboption pubs, read ony Caing sp_dboption with a database name, option name, and setting vaue turns the option on or off: sp_dboption pubs, read ony, true Exercise: Creating a Database on Two Devices Exercise waks you through the process of creating a database on two devices. The first device contains the data, and the second device contains the og. This exercise and Exercise assume that you have two devices named DataDevice and LogDevice on your system that are at east 10MB in size, and that they are empty devices. 1. Load SQL Enterprise Manager. From the Server Manager window, seect the server on which you want to create the new database. 2. Load the SQL Query too by seecting Toos, SQL Query Too from the appication s main menu. 3. Use the DB combo box to seect the Master database. 4. In the query window, type: CREATE DATABASE Exercise3 ON DataDevice = 5 LOG ON LogDevice = 2 5. Execute the query by typing At-X or cicking the Execute Query button on the query window s toobar. A 7MB database named Exercise3 is created. Five megabytes of the database store data and are ocated on the DataDevice device. The other 2MB of the database are aocated to the transaction og, which resides on the device LogDevice Exercise: Expanding a Database fie://i:\chapters\z\zc817.htm 3/21/01

10 MCSE TestPrep SQL Server 6.5 Design & Impementation - Data Definition Page 10 of 38 In Exercise 3.2.6, you expand the database you created in Exercise You expand the database in two steps: expand the og, and then expand the data. 1. If it is not aready oaded, open the SQL Query too by seecting Toos, SQL Query Too from the appication s main menu. 2. Use the DB combo box to seect the Master database. 3. In the query window, type: ALTER DATABASE Exercise3 ON LogDevice = 5 4. Execute the query by typing At-X or cicking the Execute Query button on the query window s toobar. The database s og is expanded by 5MB, for a tota og size of 7MB. 5. In the query window, type: ALTER DATABASE Exercise3 ON DataDevice = 5 6. Execute the query. The database s data area is expanded by 5MB, for a tota data size of 10MB. 7. In the query window, execute the query: exec sp_hepdb Exercise3 Note how the tota size of the database has been increased, and how the database is ocated in four fragments on two devices Practice Probems 1. Which of the foowing are true about databases and devices? A. Databases can contain more than one device. B. Different devices can reside on separate physica disks. C. Devices can contain more than one database. D. Databases can reside on more than one device. E. Databases cannot reside on devices that are on different physica disks. 2. When using the CREATE DATABASE statement, the size of the database is expressed in which of the foowing? A. The number of 2KB pages B. Megabytes C. The number of aocation units D. In units 3. What is the purpose of the FOR LOAD keyword in the CREATE DATABASE and ALTER DATABASE statements? A. It prevents changes to the database size unti after the database is oaded from a backup. B. It forces a data pages in the new database to be zeroed out in prepara- tion for a fie://i:\chapters\z\zc817.htm 3/21/01

11 MCSE TestPrep SQL Server 6.5 Design & Impementation - Data Definition Page 11 of 38 database oad. C. It oads the specified database dump into the newy created database. D. It prevents users from accessing the database unti after the database is oaded from a backup. 4. What is/are the effects of mutipe database resizings? A. Database backups can be ess reiabe. B. Mutipe database fragments make recoverabiity more difficut in the event of a Master database corruption. C. Mutipe database fragments have a negative performance impact. D. No adverse effects occur. 5. Whie adding a tabe to the database, you receive the foowing error message: "Can t aocate space for object tabename in database dbname because the defaut segment is fu." What is the best course of action? A. Expand the current data device or create a new data device. Use ALTER DATABASE to expand the database og into the new space. B. Run DBCC SHRINKDB (dbname) to recaim fragmented pages in the database. C. Expand the current data device or create a new data device. Use ALTER DATABASE to expand the database into the new space. D. Expand the current og device or create a new og device. Use ALTER DATABASE to expand the database og into the new space. 6. Whie adding a tabe to the database, you receive the foowing error message: "Can t aocate space for object tabename in database dbname because the ogsegment segment is fu." What is the best course of action? A. Expand the current data device or create a new data device. Use ALTER DATABASE to expand the database og into the new space. B. Run DBCC SHRINKDB (dbname, LOGONLY) to recaim fragmented pages in the database transaction og. C. Expand the current data device or create a new data device. Use ALTER DATABASE to expand the database into the new space. D. Expand the current og device or create a new og device. Use ALTER DATABASE to expand the database og into the new space. 7. Which user(s) can run the CREATE DATABASE and ALTER DATABASE commands? A. The system administrator B. The database owner (DBO) C. Users granted permission to use CREATE DATABASE D. Any users on the system 8. In which database must you be to execute the CREATE DATABASE, ALTER DATABASE, or DROP DATABASE command? A. Tempdb B. Master C. Mode D. The newy created database 9. Which command is used to change database options? A. ALTER DATABASE B. RECONFIGURE C. sp_configure D. sp_dboption 10. What is/are the effect(s) of turning on the "trunc. og on chkpt." option? A. Committed transactions are removed from the og about once each minute. fie://i:\chapters\z\zc817.htm 3/21/01

12 MCSE TestPrep SQL Server 6.5 Design & Impementation - Data Definition Page 12 of 38 B. The transaction og may be dumped quicky for recovery purposes. C. Users may perform non-ogged operations. D. The transaction og is ess ikey to fi up Answers and Expanations: Practice Probems 1. B, C, D Different database devices can reside on separate physica disks; each device can contain more than one database; each database can be spread out over more than one device. 2. B The size of SQL Server databases is expressed in megabytes. 3. D The FOR LOAD keyword in the CREATE DATABASE statement prevents users from accessing the database unti after the database is oaded from a backup. 4. B Mutipe database resizings create mutipe database fragments, which makes recoverabiity more difficut in the event of a Master database corruption. 5. C Expand the current data device or create a new data device. Use ALTER DATABASE to expand the database into the new space. 6. D Expand the current og device or create a new og device. Use ALTER DATABASE to expand the database og into the new space. 7. A, C By defaut the system administrator is granted permission to use the CREATE DATABASE and the ALTER DATABASE commands; permissions to use these commands are aso transferred to users who have been granted permission to use CREATE DATABASE. 8. B You must be in the Master database to issue the CREATE DATABASE, ALTER DATABASE, and the DROP DATABASE commands. 9. D sp_dboption is used to set database options. 10. A, D Committed transactions are removed from the og about once each minute and the transaction og is ess ikey to fi up Keywords Enterprise Manager Master database Mode database 3.3 Understanding Datatypes Before creating tabes in a database, it is hepfu to understand what kinds of data can be stored in SQL Server. SQL Server uses 19 different datatypes to identify the type of information (be it numeric, character-based, or some other type) stored in a coumn. In addition, database users can define their own datatypes based on the system-suppied datatypes. fie://i:\chapters\z\zc817.htm 3/21/01

13 MCSE TestPrep SQL Server 6.5 Design & Impementation - Data Definition Page 13 of 38 Datatypes aso are used to define the type of data passed as a parameter to a stored procedure or the type of data used in a oca variabe System Datatypes The 19 system datatypes can be grouped into seven broad categories. For more information about each specific datatype, see the SQL Server Books Onine User-Defined Datatypes SQL Server enabes you to define custom datatypes. User-defined datatypes hep ensure that simiar coumns have the same datatype, NULL option, defaut, and rue, and hep document the database. A user-defined datatype has the foowing characteristics: Base Type: This defines the main SQL Server datatype for the user-defined type (UDT). Nu Option: Specifies the defaut NULL option for coumns that use this user-defined type. The UDT NULL option can be overridden when a tabe is created or changed. Rue: A UDT may have a rue bound to it that defines a range of vaues acceptabe for the coumn. For more information about rues, see Chapter 8, "Using Views, Defauts, and Rues." Defaut: A UDT may have a defaut bound to it that defines an initia vaue for the coumn. Defaut vaues are most often used with coumns that do not aow NULLs. For more information about defauts, see Chapter 8. UDTs may be added and deeted through Enterprise Manager, or by using the sp_addtype and sp_droptype system stored procedures Practice Probems 1. What are the Transact-SQL commands used to create and deete user-defined datatypes? A. CREATE UDDT and DROP UDDT B. sp_bindtype and sp_droptype C. sp_addtype and sp_droptype D. sp_addtype and sp_unbindtype 2. What are some benefits of user-defined types? A. UDTs give SQL Server the fexibiity to store future datatypes. B. UDTs hep document a database. C. UDTs provide consistent coumn properties for simiar coumns. D. UDTs hep enforce coumn naming conventions. 3. Datatypes are used to define which of the foowing? A. The type of information stored in a tabe s coumn B. The type of information used in a oca variabe C. The type of information passed between triggers and tabes D. The type of information used in a stored procedure s parameters 4. How many different datatypes does SQL Server support? A. 10 fie://i:\chapters\z\zc817.htm 3/21/01

14 MCSE TestPrep SQL Server 6.5 Design & Impementation - Data Definition Page 14 of 38 B. 9 C. 19 D. 17 E What purposes, other than defining a coumn s data, do datatypes serve? A. They can be used as keys for indices. B. They can determine the type of data used in a variabe. C. They define a stored procedure parameter s datatype. D. They uniquey name a row. 6. Into how many broad categories can SQL Server s buit-in datatypes be paced? A. 5 B. 7 C. 3 D. 4 E How many bytes of information can the varbinary datatype store? A B. 255 C. 512 D. 768 E What is the difference between a char datatype and a varchar datatype? A. One hods more information than the other. B. One can be used as an array of characters. C. One requires ess storage than the other. D. One is not fixed-ength. 9. How many datatypes can a coumn have in a tabe? A. 1 B. 3 C. 255 D Which of these is one of the ways you can add a user-defined type to a SQL Server database? A. Using the ADD UDT Transact-SQL command B. Using the sp_addudt system stored procedure C. Through Enterprise Manager D. Using the sp_newdatatype system stored procedure Answers and Expanations: Practice Probems 1. C The sp_addtype and sp_droptype system stored procedures are used to manipuate userdefined types. 2. B, C UDTs hep document a database and provide consistent coumn properties for simiar coumns. 3. A, B, D Datatypes define the type of information stored in a tabe's coumn, the type of information used in a oca variabe, and the type of information used in a stored procedure's parameters. fie://i:\chapters\z\zc817.htm 3/21/01

15 MCSE TestPrep SQL Server 6.5 Design & Impementation - Data Definition Page 15 of C SQL Server has 19 pre-defined datatypes. 5. C Another use for a datatype is to define a stored procedure parameter's datatype. 6. B SQL Server datatypes can be grouped into seven main categories. 7. B The varbinary datatype can store up to 255 bytes of data. 8. D The difference between the char and varchar datatypes is that the varchar datatype is not fixed-ength. 9. A Each coumn in a tabe can have ony one datatype. 10. C Enterprise Manager can aso be used to add user-defined datatypes Keywords Datatypes Binary system datatype Character system datatype Date & Time system datatype Exact Numeric system datatype Foating Point (approximate numeric) system datatype Integer system datatype Specia system datatype 3.4 Managing Tabes After you finish defining the physica storage for a database, you add tabes and other objects to your database to impement the data mode. Tabes are used to store a the data in a database and are the most structuray compex of a the database objects. The remainder of this chapter covers how tabes are impemented in SQL Server, and how data integrity is maintained. When working with tabes, it is hepfu to remember these facts: Tabe names may be up to 30 characters in ength, and must be unique in a database. A tabe may contain up to 250 coumns, and the combined row ength (sum of a of the bytes of storage for a coumns) may not be more than 1,962 bytes. Coumn names must be unique within a tabe. A SQL Server database may contain up to two biion tabes (athough a database with this many tabes woud be difficut to administer). Each coumn in a tabe has four important characteristics. The first is the coumn name--this identifies the coumn in the tabe. Next, the coumn datatype specifies the type of information stored in the coumn. The coumn s NULL option defines whether the coumn can contain NULLs. Finay, the coumn may have one or more constraints associated with it. Constraints are discussed ater in this fie://i:\chapters\z\zc817.htm 3/21/01

16 MCSE TestPrep SQL Server 6.5 Design & Impementation - Data Definition Page 16 of 38 chapter Creating a Tabe When you create a tabe, you are reay defining the tabe s structure in terms of its coumns. This can be done by using the Transact SQL CREATE TABLE statement. The simpified syntax of the CREATE TABLE command is: CREATE TABLE [database.[owner].]tabe_name ( {co_name datatype [nu_option] [[, next_co_name datatype [nu_option]]...]} ) Constraints can aso be defined in the CREATE TABLE statement--the syntax is covered ater in the chapter. Every coumn must be named and have a datatype defined. If no NULL option is specified, the coumn defauts to disaow NULLs. Note that enabing the ANSI Nu Defaut database option causes tabe coumns to aow NULLs if no NULL option is specified for the coumn Modifying a Tabe After you create a tabe, you may modify its structure by adding coumns and adding, changing, or removing constraints. Be aware of these two restrictions when atering the coumns in a tabe: You may add a coumn ony if its NULL option is set to aow NULLs. You may add a new IDENTITY coumn to the tabe if one does not exist, but you may not change an existing coumn to an IDENTITY coumn. (IDENTITY coumns are covered in more detai ater in the chapter.) If you need to add a non-null coumn to a tabe, you must drop and re-create the tabe. The Transact-SQL ALTER TABLE statement is used to modify an existing tabe. The simpified syntax of the ALTER TABLE command is as foows: ALTER TABLE [database.[owner].]tabe_name ( ADD {co_name datatype [nu_option] [[, next_co_name datatype [nu_option]]...]} ) Constraints aso can be defined in the ALTER TABLE statement. Every coumn must be named and have a datatype defined. Coumns added using the ALTER TABLE statement must aow NULLs Dropping a Tabe A tabe may be dropped (deeted) from a database by its owner, the system administrator, or the DBO. When a tabe is dropped, a data, indexes, triggers, and constraints associated with the tabe aso are deeted. To drop a tabe using Transact-SQL, the DROP TABLE command is used. The syntax for the DROP TABLE command is as foows: DROP TABLE <tabename> fie://i:\chapters\z\zc817.htm 3/21/01

17 MCSE TestPrep SQL Server 6.5 Design & Impementation - Data Definition Page 17 of Exercise: Creating a Tabe In Exercise 3.4.4, you create a tabe to store a company s empoyee information. This tabe is created in the database you created in Exercise If it is not aready oaded, open the SQL Query too by seecting Toos, SQL Query Too from the appication s main menu. 2. Use the DB combo box to seect the Exercise3 database. If the database does not show up in the ist, choose the <refresh> option to refresh the ist of databases. Then, choose the Exercise3 database. 3. Type the foowing query in the query window: CREATE TABLE Empoyee ( FirstName LastName MiddeInitia SociaSecurityNumber HireDate ) varchar(30) NOT NULL, varchar(30) NOT NULL, char(1) NULL, char(11) NOT NULL, datetime NULL 4. Execute the query by typing At-X or cicking the Execute Query button on the query window s toobar. The Empoyee tabe is created. 5. In the query window, execute this query: exec sp_hep Empoyee 6. Check to ensure that the coumns were created with the proper datatypes and NULL options Exercise: Creating a Tabe Using Enterprise Manager 1. In the Server Manager window, seect the server that contains the database to which you want to add the tabe. Expand the tree view by cicking on the pus sign to the eft of the server name. 2. Expand the Databases foder by cicking the pus sign to the eft of the foder icon. A ist of a the server s databases appears. 3. Seect the database to which you want to add the tabe. Cick the pus sign to the eft of the database icon to expand the tree view. Cick the pus sign next to the Objects foder to show a ist of a database objects. 4. Right-cick the Tabes foder so that the context menu appears. Seect the New Tabe option. 5. Define each coumn for the tabe by typing a coumn name in the grid, seecting a datatype, entering a datatype size (for some datatypes), entering a NULL option, and entering a defaut. 6. When you are done entering the coumns for the tabe, cick the Save Tabe button on the window s toobar. The Specify Tabe Name diaog box appears and prompts you to name the new tabe. 7. Enter the name of the new tabe and cick OK. The tabe is added to the database. fie://i:\chapters\z\zc817.htm 3/21/01

18 MCSE TestPrep SQL Server 6.5 Design & Impementation - Data Definition Page 18 of Practice Probems 1. SQL Server maintains what types of information about a coumn in the tabe definition? A. Name, NULL option, and con- straints B. Name, datatype, and NULL option C. Name, datatype, NULL option, and bytes of overhead D. Name, datatype, NULL option, and constraints 2. What statement(s) are not true about tabes and coumns? A. A tabe may contain up to 250 coumns. B. Coumn names must be unique within the database. C. Tabe and coumn names can be up to 30 characters in ength. D. A tabe definition is reay just a coection of coumn definitions. 3. The Transact-SQL command used to create tabes is caed which of the foowing? A. INITIALIZE TABLE B. ALLOCATE TABLE C. DECLARE TABLE D. MAKE TABLE E. CREATE TABLE 4. What is the defaut NULL option for a coumn, if it is not defined? A. NULLs are aowed for a non- identity fieds. B. NULLs are disaowed for a non- identity fieds. C. NULLs are aowed for integer fieds. D. NULLs are aowed for character fieds ony. 5. What are two restrictions when atering a tabe? A. You may add ony coumns that aow NULLs. B. You may add an IDENTITY coumn ony if one does not aready exist. C. You may add ony non-unique coumns. D. You may add a binary coumn ony if one does not aready exist. 6. What is the maximum ength for a tabe name in SQL Server? A. 40 characters B. 255 characters C characters D. 30 characters 7. Which of these statements about tabes is not true? A. A coumns must have a datatype. B. Tabes can contain up to 250 coumns. C. Coumn names do not have to be unique. D. The combined row ength cannot be more than 1962 bytes. 8. How many tabes can a SQL Server database contain? A B. 2 Biion C D. 512 E What is the Transact-SQL command that is used for modifying a tabe? A. MODIFY TABLE B. CHANGE TABLE C. REDEFINE TABLE fie://i:\chapters\z\zc817.htm 3/21/01

19 MCSE TestPrep SQL Server 6.5 Design & Impementation - Data Definition Page 19 of 38 D. ALTER TABLE 10. Who is aowed to deete tabes from a SQL Server database? (Choose a that appy.) A. The tabe owner B. The system administrator C. The database owner D. Users with write access 11. What is the Transact-SQL command for deeting tabes? A. DELETE TABLE B. REMOVE TABLE C. EXPUNGE TABLE D. DROP TABLE E. EXCLUDE TABLE 12. When atering the structure of a tabe, which of the foowing rues appy? (Choose two.) A. New coumns may be added with either NULL option. B. New coumns may be added ony if they aow NULLs. C. An existing coumn may be con- verted to an IDENTITY coumn. D. Coumns of the timestamp datatype cannot be added. E. A new IDENTITY coumn may be added if one does not aready exist. 13. What is the purpose of the WITH NOCHECK option in the ALTER TABLE statement? A. A constraint checking is disabed to improve performance. B. Constraint checking is turned off for the tabe unti turned back on with the WITH CHECK keyword. C. PRIMARY KEY and UNIQUE constraints are not checked for the duration of the tabe modification. D. CHECK and FOREIGN KEY / REFERENCE constraints are not checked for the duration of the tabe modification Answers and Expanations: Practice Probems 1. D SQL Server maintains Name, datatype, NULL option, and constraint information in a coumn definition. 2. B Coumn names must be unique within the database. 3. E CREATE TABLE is the command used to create tabes in TRANSACT-SQL. 4. B Nus are disaowed for a non-identity fieds. 5. A, B You may add ony coumns that aow NULLs and you may add an IDENTITY coumn ony if one does not aready exist. 6. D Thirty characters is the maximum ength of a tabe name in SQL Server. 7. C Coumn names must be unique within a tabe. 8. B A SQL Server database can contain 2 biion tabes. 9. D The Transact-SQL command to modify a tabe is caed ALTER TABLE. 10. A, B, C The tabe owner, the system administrator, and the database owner are the ony fie://i:\chapters\z\zc817.htm 3/21/01

20 MCSE TestPrep SQL Server 6.5 Design & Impementation - Data Definition Page 20 of 38 users aowed to deete tabes in a SQL Server databases. 11. D The Transact-SQL command used to deete a tabe is DROP TABLE. 12. B, E New coumns may be added ony if they aow NULLs and a new IDENTITY coumn may be added ony if one does not aready exist. 13. D The purpose of the WITH NOCHECK option is to denote that CHECK and FOREIGN KEY / REFERENCE constraints are not checked for the duration of the tabe modification Keywords Database tabe NULL options NOT NULL coumn ALTER TABLE statement 3.5 Using Constraints Data integrity is an important concept to keep in mind when designing a database. Data integrity is a broad term that simpy refers to the correctness of data in a database. One of the benefits of using SQL Server is that a the data integrity rues can be defined in a centra ocation--namey, the database. There are three main types of data integrity: Entity integrity: One of the requirements in a reationa database design is the capabiity to distinguish different instances of an entity. This concept is known as entity integrity, and it is accompished by creating a primary key in a tabe. Domain integrity: Concerned with ensuring that coumn vaues fa within an acceptabe range of vaues (the domain). "Domain integrity" aso refers to the datatype and NULLabiity of a coumn. Referentia integrity: Refers to the requirement that primary and foreign keys remain synchronized between parent and chid tabes. SQL Server supports two different impementations of data integrity, as described: Procedura data integrity is avaiabe in a versions of SQL Server. It reies on views, triggers, stored procedures, defauts, and rues to enforce domain and referentia integrity. Procedura data integrity is the most fexibe, but incurs the most execution overhead and can be error prone. Decarative data integrity was introduced in SQL Server 6.0 via constraints. Constraints provide a concise, consistent way to manage a three types of data integrity by extending the SQL syntax used to create and modify tabes. In other words, the data integrity is decared when a tabe is created. Constraints are ess error-prone and incur ess execution overhead than procedura methods; however, constraints are ess fexibe. fie://i:\chapters\z\zc817.htm 3/21/01

21 MCSE TestPrep SQL Server 6.5 Design & Impementation - Data Definition Page 21 of 38 There are no ceary defined rues for when one type of data integrity shoud be used over another. Usuay, a mix of methods is used. The remainder of the chapter covers the different types of constraints and how they enforce each type of data integrity Managing Tabe Constraints As mentioned previousy, constraints may be created on a tabe when the tabe is initiay defined. Another benefit of constraints is that they may be added or removed from the tabe without dropping or modifying the tabe itsef. Using the Transact-SQL CREATE TABLE and ALTER TABLE statements gives you the most fexibiity in defining constraints, athough you may find that using Enterprise Manager s Manage Tabes window is easier. When using constraints in a database impementation, be aware that constraint names must be unique in the database. If you do not expicity assign a name to a constraint, SQL Server provides one, such as PK mytabe 2CD2B24E. These system-suppied names can make administering constraints more difficut. NOTE: Use the system stored procedure sp_hep or sp_hepconstraint to see each constraint paced on a tabe Adding and Dropping Constraints with Transact-SQL The preceding discussions of the CREATE TABLE and ALTER TABLE statements excuded the syntax used to manage tabe constraints. This section shows you the fu syntax diagram for each statement and gives exampes of adding and dropping constraints on a tabe. More detaied Transact- SQL syntax is shown for each constraint type ater in the chapter. When using Transact-SQL statements to manage constraints, you either decare constraints at the coumn eve or the tabe eve. Where you decare the constraint has no bearing on how it functions; the syntax is merey different. Constraints that invove more than one coumn must be decared at the tabe eve. Decaring Constraints Constraints are usuay first decared when a tabe is created with the CREATE TABLE statement. Here is the fu syntax for CREATE TABLE: CREATE TABLE [database.[owner].]tabe_name ({co_name coumn_properties [co_constraint [co_constraint [...co_constraint]]] [[,] tabe_constraint]} [[,] {next_co_name next_tabe_constraint}...] ) Note that constraints may be decared in ine with the coumn definition, such as: EmpoyeeSaary money not nu CHECK (EmpoyeeSaary > 0) DEFAULT This exampe defines both a CHECK constraint and a DEFAULT constraint on the EmpoyeeSaary coumn. Both constraints are said to be defined at the coumn eve. Typicay, coumn-eve fie://i:\chapters\z\zc817.htm 3/21/01

22 MCSE TestPrep SQL Server 6.5 Design & Impementation - Data Definition Page 22 of 38 constraints are used when possibe, because they make the CREATE TABLE statement easier to read. Constraints decared at the tabe eve may be interspersed with the coumn definitions, or may be incuded at the end of the coumn definitions in the statement. This exampe shows a PRIMARY KEY constraint and a UNIQUE constraint both decared at the tabe eve: CREATE TABLE Empoyee ( EmpoyeeID int IDENTITY, PRIMARY KEY (EmpoyeeID), FirstName char(30), LastName char(30), SociaSecNumber char(11), CONSTRAINT UQ_EmpoyeeSSN UNIQUE (SociaSecNumber) ) Typicay, a tabe-eve constraints are incuded at the end of the coumn ist to improve readabiity. Note that in the preceding exampe, a name was expicity assigned (UQ_EmpoyeeSSN) to the UNIQUE constraint on the socia security number coumn. Dropping and Adding Constraints You may use the ALTER TABLE statement to add or drop constraints after a tabe has been created. The fu syntax of ALTER TABLE foows: ALTER TABLE [database.[owner].]tabe_name [WITH NOCHECK] [ADD {co_name coumn_properties [coumn_constraints] [[,] tabe_constraint]} [, {next_co_name next_tabe_constraint}]...] [DROP [CONSTRAINT] constraint_name [, constraint_name2]...] You have aready seen how to add coumns by using the ALTER TABLE statement. When you add new coumns with constraints, or add new tabe-eve constraints, the syntax used to describe coumns and constraints is exacty the same as the CREATE TABLE syntax. Dropping a constraint is straightforward. Executing the foowing statement drops the unique constraint defined earier on the Empoyee tabe: ALTER TABLE Empoyee DROP CONSTRAINT UQ_EmpoyeeSSN It is important to note that the WITH NOCHECK option in the ALTER TABLE statement disabes constraint checking for FOREIGN KEY and CHECK constraints during the tabe s modification. This enabes these constraints to be added even if the existing data vioates these constraints. This option is typicay used when a tabe is arge and the data is aready known to be accurate. Disabing constraint checking when modifying the tabe improves the speed of the modification. The NOCHECK option has no effect on PRIMARY KEY, UNIQUE, or DEFAULT constraints Using an IDENTITY Coumn fie://i:\chapters\z\zc817.htm 3/21/01

23 MCSE TestPrep SQL Server 6.5 Design & Impementation - Data Definition Page 23 of 38 Technicay, the IDENTITY property for a coumn is not a constraint, it is a third setting for a coumn s NULL option. Nevertheess, IDENTITY coumns are often used to provide entity integrity, so they are incuded in this section. An IDENTITY coumn is a specia coumn in a tabe that provides a sequentia, auto-incrementing number generated every time a record is inserted into the tabe. The number for a new row is determined by taking the ast vaue in the coumn and adding an increment vaue suppied during the coumn s definition. Keep the foowing characteristics in mind when using IDENTITY coumns: A tabe can have ony one IDENTITY coumn. The coumn must use an integer datatype (int, smaint, or tinyint) or an exact numeric datatype (numeric, decima) with no fractiona component. In other words, the coumn must contain ony whoe numbers. The coumn is automaticay restricted from containing NULLs. The coumn cannot be updated. Do not confuse an IDENTITY coumn with a coumn containing a timestamp. A new timestamp vaue is suppied when a coumn is inserted or updated. The IDENTITY coumn suppies vaues ony when a row is inserted. By itsef, an IDENTITY coumn does not enforce entity integrity. The IDENTITY property just causes a coumn to suppy auto-incrementing numbers usefu as surrogate key vaues. However, pacing a PRIMARY KEY or UNIQUE constraint on the coumn enabes it to enforce entity integrity. Creating an IDENTITY Coumn An IDENTITY coumn is created when a tabe is created with the CREATE TABLE statement, or when a tabe is modified via an ALTER TABLE statement. Reca that the syntax for creating a coumn in either one of these statements takes on the foowing form: coumn_name data_type [nu_option] Adding the IDENTITY option into the syntax diagram gives you the foowing: coumn_name data_type [ {nu_option IDENTITY [(seed,increment)]} ] The seed and increment vaues are optiona. If one is specified, both must be specified. The seed vaue indicates what the vaue of the IDENTITY coumn wi be after the first row is inserted into the tabe. The increment vaue specifies the step used to increment to the next vaue in the coumn. If these vaues are omitted, seed and increment both defaut to 1. Here are some exampes of CREATE TABLE statements using IDENTITY coumns: This exampe creates a tabe with severa coumns. The first coumn, ID, is an IDENTITY coumn with seed and increment of 1: fie://i:\chapters\z\zc817.htm 3/21/01