Oracle in a Nutshell

RESTRICT_REFERENCES Pragma

Prior to Oracle8i, it was necessary to assert the purity level of a packaged procedure or function when using it directly or indirectly in a SQL statement. Beginning with Oracle8i, the PL/SQL runtime engine determines a program’s purity level automatically if no assertion exists. The RESTRICT REFERENCES pragma is still supported for backwards compatibility but it has been deprecated in Oracle9i.

The RESTRICT_REFERENCES pragma asserts a purity level. The syntax for the RESTRICT_REFERENCES pragma is:

PRAGMA RESTRICT_REFERENCES (program_name | DEFAULT, purity_level);

The keyword DEFAULT applies to all methods of an object type or all programs in a package.

You can specify from one to five purity levels, in any order, in a comma-delimited list. The purity level describes to what extent the program or method is free of side effects. Side effects are listed in the Table 9-3 with the purity levels they address.

Table 9-3. Purity levels and side effects

Purity level	Description	Restriction
WNDS	Write No Database State	Executes no INSERT, UPDATE, or DELETE statements
RNDS	Read No Database State	Executes no SELECT statements
WNPS	Write No Package State	Does not modify any package variables
RNPS	Read No Package State	Does not read any package variables
TRUST		Does not enforce the restrictions declared but allows the compiler to trust they are true