2.6 The PRAGMA Keyword

The PRAGMA keyword is used to signify that the remainder of the PL/SQL statement is a pragma, or directive, to the compiler. Pragmas are processed at compile time; they do not execute during runtime.

A pragma is a special instruction to the compiler. Also called a pseudoinstruction, the pragma doesn't change the meaning of a program. It simply passes information to the compiler. It is very similar, in fact, to the tuning hints you can embed in a SQL statement inside a block comment.

PL/SQL offers the following pragmas:

EXCEPTION_INIT

Tells the compiler to associate a particular error number with an identifier you have declared as an exception in your program. See Chapter 8, Exception Handlers for more information.

RESTRICT_REFERENCES

Tells the compiler the purity level (freedom from side effects) of a packaged program. See Chapter 17, Calling PL/SQL Functions in SQL for more information.

SERIALLY_REUSABLE

New to PL/SQL8. Tells the PL/SQL runtime engine that package-level data should not persist between references to that data. See Chapter 25, Tuning PL/SQL Applications for more information.

The syntax for using the PRAGMA keyword is as follows:

PRAGMA <instruction>;

where <instruction> is a statement providing instructions to the compiler. You would call EXCEPTION_INIT as follows:

DECLARE    no_such_sequence EXCEPTION;    PRAGMA EXCEPTION_INIT (no_such_sequence, -2289); BEGIN    ... END;