SET CONSTRAINTSQL)- Language Statements (2002-1SET2CONSTRAINTS(l)
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 INITIALLY 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 modifications 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 immediate 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.
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