The PRAGMA Keyword

A programming notion that is truly derived from Greek is pragma, which means “deed”

or, by implication, an “action.” In various programming languages, a pragma is gen-

erally a line of source code prescribing an action you want the compiler to take. It’s like

an option that you give the compiler; it can result in different runtime behavior. for the

program, but it doesn’t get translated directly into bytecode.

PL/SQL has a PRAGMA keyword with the following syntax:

PRAGMA instruction_to_compiler;

The PL/SQL compiler will accept such directives anywhere in the declaration section,

but most of them have certain additional requirements regarding placement.

PL/SQL offers several pragmas:

AUTONOMOUS_TRANSACTION

Tells the PL/SQL runtime engine to commit or roll back any changes made to the

database inside the current block without affecting the main or outer transaction.

EXCEPTION_INIT

Tells the compiler to associate a particular error number with an identifier you have

declared as an exception in your program. Must follow the declaration of the

exception.

RESTRICT_REFERENCES

Tells the compiler the purity level (freedom from side effects) of a packaged pro-

gram.

SERIALLY_REUSABLE

Tells the PL/SQL runtime engine that package-level data should not persist be-

tween references to that data. See Chapter 18 for more information.

The following block demonstrates the use of the EXCEPTION_INIT pragma to name

a built-in exception that would otherwise have only a number:

DECLARE

no_such_sequence EXCEPTION;

PRAGMA EXCEPTION_INIT (no_such_sequence, −2289);

BEGIN

...

EXCEPTION

WHEN no_such_sequence

THEN

q$error_manager.raise_error ('Sequence not defined');

END;

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The PRAGMA Keyword