Oracle7 Server SQL Reference

Comments

You can associate comments with SQL statements and schema objects.

Comments Within SQL Statements

Comments within SQL statements do not affect the statement execution, but they may make your application easier for you to read and maintain. You may want to include a comment in a statement that describes the statement's purpose within your application.

A comment can appear between any keywords, parameters or punctuation marks in a statement. You can include a comment in a statement using either of these means:

Begin the comment with /*. Proceed with the text of the comment. This text can span multiple lines. End the comment with */. The opening and terminating characters need not be separated from the text by a space or a line break.

Begin the comment with -- (two hyphens). Proceed with the text of the comment. This text cannot extend to a new line. End the comment with a line break.

A SQL statement can contain multiple comments of both styles. The text of a comment can contain any printable characters in your database character set.

You can use comments in a SQL statement to pass instructions, or hints, to the Oracle7 optimizer. The optimizer uses these hints to choose an execution plan for the statement. For more information on hints, see the "Tuning SQL Statements" chapter of Oracle7 Server Tuning.

Note that you cannot use these styles of comments between SQL statements in a SQL script. You can use the Server Manager or SQL*Plus REMARK command for this purpose. For information on these commands, see Oracle Server Manager User's Guide or SQL*Plus User's Guide and Reference.

Example

These statements contain many comments:

SELECT ename, sal + NVL(comm, 0), job, loc

/* Select all employees whose compensation is

greater than that of Jones.*/

	FROM emp, dept

		 /*The DEPT table is used to get the department name.*/

	WHERE emp.deptno = dept.deptno

	  AND sal + NVL(comm,0) >	 /* Subquery:		   */

   (SELECT sal + NLV(comm,0)

   /* total compensation is sal + comm */

			FROM emp

			WHERE ename = 'JONES')

SELECT ename,			-- select the name

		sal + NVL(comm, 0)		-- total compensation

		job				-- job

		loc				-- and city containing the office

	FROM emp,			-- of all employees

	     dept

	WHERE emp.deptno = dept.deptno

	  AND sal + NVL(comm, 0) >	-- whose compensation

						-- is greater than

	    (SELECT sal + NVL(comm,0)	-- the compensation

		FROM emp

		WHERE ename = 'JONES') 	-- of Jones.

Comments on Schema Objects

You can associate a comment with a table, view, snapshot, or column using the COMMENT command described

, "Commands" of this manual. Comments associated with schema objects are stored in the data dictionary.