redhat man page for set_constraints

SET 
CONSTRAINTS(7)						   SQL Commands 						SET CONSTRAINTS(7)

NAME
       SET CONSTRAINTS - set the constraint mode of the current transaction

SYNOPSIS
       SET CONSTRAINTS { ALL | constraint [, ...] } { DEFERRED | IMMEDIATE }

DESCRIPTION
       SET  CONSTRAINTS  sets  the behavior of constraint evaluation in the current transaction. In IMMEDIATE mode, constraints are checked at the
       end of each statement. In DEFERRED mode, constraints are not checked until transaction commit.

	      Note: This command only alters the behavior of constraints within the current transaction. Thus, if you execute this command outside
	      of an explicit transaction block (such as one started with BEGIN), it will not appear to have any effect.  If you wish to change the
	      behavior of a constraint without needing to issue a SET CONSTRAINTS command in every transaction, specify INITIALLY DEFERRED or INI-
	      TIALLY IMMEDIATE when you create the constraint.

       When you change the mode of a constraint to be IMMEDIATE , the new constraint mode takes effect retroactively: any outstanding data modifi-
       cations that would have been checked at the end of the transaction (when using DEFERRED) are instead checked during the	execution  of  the
       SET CONSTRAINTS command.

       Upon  creation,	a constraint is always give one of three characteristics: INITIALLY DEFERRED, INITIALLY IMMEDIATE DEFERRABLE, or INITIALLY
       IMMEDIATE NOT DEFERRABLE. The third class is not affected by the SET CONSTRAINTS command.

       Currently, only foreign key constraints are affected by this setting. Check and unique constraints are always effectively initially immedi-
       ate not deferrable.

COMPATIBILITY
   SQL92, SQL99
       SET  CONSTRAINTS is defined in SQL92 and SQL99. The implementation in PostgreSQL complies with the behavior defined in the standard, except
       for the PostgreSQL limitation that SET CONSTRAINTS cannot be applied to check or unique constraints.

SQL - Language Statements					    2002-11-22							SET CONSTRAINTS(7)