SET CONSTRAINTSSQL - Language StatementsSET CONSTRAINTSset the constraint mode of the current transaction2000-06-01
SET CONSTRAINTS { ALL | constraint [, ...] } { DEFERRED | IMMEDIATE }
DescriptionSET CONSTRAINTS sets the behavior of constraint
evaluation in the current transaction. In mode, constraints are checked at the end of each
statement. In mode, constraints are not
checked until transaction commit.
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 or
when you create the constraint.
When you change the mode of a constraint to be , the new constraint mode takes effect retroactively:
any outstanding data modifications that would have been checked
at the end of the transaction (when using
) are instead checked during the
execution of the SET CONSTRAINTS command.
Upon creation, a constraint is always give one of three
characteristics: ,
, or
. 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.
CompatibilitySQL92, SQL99SET 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.