Understanding SQL Keywords

SQL keywords are words that have a special significance in SQL and should not be used as user-defined names for database objects such as tables, columns, domains, constraints, procedures, variables, and so on. There are two types of keywords, reserved and nonreserved. The difference between reserved and nonreserved keywords is that some database products let you (although you should not) use nonreserved keywords to name database objects and variables. To make your SQL statements portable and less confusing, avoid using reserved words as identifiers.

When writing SQL statements, use all capital letters for keywords and lowercase letters for nonkeywords (or vice versa). Keywords are case-insensitive, meaning that the DBMS will recognize a keyword whether you type it using all capital letters, lowercase letters, or a combination of both. Making the case (capital vs. lower case) of reserved words different than non-reserved words in SQL statements makes the SQL statements easier for you (and those responsible for maintaining your database creation) to read.

Since each DBMS product supports most SQL-92 reserved words and adds a few of its own, the system manual and online help system are your best source for a list of reserved words. For example, to review MS-SQL Server's list of reserved words, perform the following steps:

1. Click on the Start button. Windows will display the Start menu.

2. Select Programs, Microsoft SQL Server 7.0 option, and click on Books Online. Windows will start the MS-SQL Server Help system.

3. Click on the Index tab and enter KEYWORDS in the Type in the Keyword to Find field. The MS-SQL Server Help system will display an alphabetical list of terms starting with Keywords.

4. To see a list of reserved keywords, click on Reserved and then click on the DISPLAY button. The Help system will display a dialog box asking you to select the type of reserved words on which you want its assistance.

5. Click on Reserved Keywords (T-SQL) and then click on the DISPLAY button. The MS-SQL Server Help system will display a list of T-SQL (Transact-SQL) reserved words, followed by a list of ODBC reserved words. The ODBC reserved words include the SQL-92 reserved words that MS-SQL Server supports. (Transact-SQL is MS-SQL Server's own procedural SQL language; Oracle uses PL/SQL and SQL Plus*.)

To exit the Help system, click on the close button (the X) in the upper-right corner of the Help application window.