RESTRICT_REFERENCES Pragma

The RESTRICT_REFERENCES pragma asserts that a user-defined subprogram does not read or write database tables or package variables.

Subprograms that read or write database tables or package variables are difficult to optimize, because any call to the subprogram might produce different results or encounter errors.

Topics:

• Syntax

• Semantics

• Usage

Syntax

restrict_references_pragma ::=

Semantics

subprogram_name

The name of a user-defined subprogram, typically a function.

If subprogram_name is overloaded, the pragma applies only to the most recent subprogram declaration.

DEFAULT

Specifies that the pragma applies to all subprograms in the package specification or ADT specification (including the system-defined constructor for ADTs).

If you also declare the pragma for an individual subprogram, it overrides the DEFAULT pragma for that subprogram.

RNDS

Asserts that the subprogram reads no database state (does not query database tables).

WNDS

Asserts that the subprogram writes no database state (does not modify tables).

RNPS

Asserts that the subprogram reads no package state (does not reference the values of packaged variables)

You cannot specify RNPS if the subprogram invokes the SQLCODE or SQLERRM function.

WNPS

Asserts that the subprogram writes no package state (does not change the values of packaged variables).

You cannot specify WNPS if the subprogram invokes the SQLCODE or SQLERRM function.

TRUST

Asserts that the subprogram can be trusted not to violate one or more rules.

When you specify TRUST, the subprogram body is not checked for violations of the constraints listed in the pragma. The subprogram is trusted not to violate them. Skipping these checks can improve performance. TRUST is needed for functions written in C or Java that are invoked from PL/SQL, since PL/SQL cannot verify them at run time.

Usage

A RESTRICT_REFERENCES pragma can appear only in a package specification or ADT specification. Typically, this pragma is specified for functions. If a function calls procedures, specify the pragma for those procedures also.

To invoke a subprogram from parallel queries, you must specify all four constraints—RNDS, WNDS, RNPS, and WNPS. No constraint implies another.