set_constraints(5)

NAME

       SET  CONSTRAINTS - set constraint checking modes for the current trans-
       action

SYNOPSIS

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

DESCRIPTION

       SET CONSTRAINTS sets the behavior of  constraint  checking  within  the
       current  transaction.  IMMEDIATE  constraints are checked at the end of
       each statement. DEFERRED constraints are not checked until  transaction
       commit. Each constraint has its own IMMEDIATE or DEFERRED mode.

       Upon  creation,  a  constraint  is  given one of three characteristics:
       DEFERRABLE INITIALLY DEFERRED, DEFERRABLE INITIALLY IMMEDIATE,  or  NOT
       DEFERRABLE.  The third class is always IMMEDIATE and is not affected by
       the SET CONSTRAINTS command. The first two classes start every transac-
       tion  in the indicated mode, but their behavior can be changed within a
       transaction by SET CONSTRAINTS.

       SET CONSTRAINTS with a list of constraint names  changes  the  mode  of
       just  those  constraints  (which  must  all be deferrable). The current
       schema search path is used to find the first matching name if no schema
       name  is  specified.  SET  CONSTRAINTS  ALL  changes  the  mode  of all
       deferrable constraints.

       When SET CONSTRAINTS changes the mode of a constraint from DEFERRED  to
       IMMEDIATE,  the  new  mode  takes effect retroactively: any outstanding
       data modifications that would have been  checked  at  the  end  of  the
       transaction  are  instead  checked during the execution of the SET CON-
       STRAINTS command.  If any such constraint is  violated,  the  SET  CON-
       STRAINTS  fails  (and  does  not change the constraint mode). Thus, SET
       CONSTRAINTS can be used to force checking of constraints to occur at  a
       specific point in a transaction.

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

NOTES

       This command only alters the behavior of constraints within the current
       transaction. Thus, if you execute this command outside of a transaction
       block (BEGIN/COMMIT pair), it will not appear to have any effect.

COMPATIBILITY

       This command complies with the behavior defined in  the  SQL  standard,
       except  for the limitation that, in PostgreSQL, it only applies to for-
       eign-key constraints.

SQL - Language Statements         2008-06-08                 SET CONSTRAINTS()