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



NAME
       SET CONSTRAINTS - set constraint checking modes for the current transaction


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 transaction 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  retroac-
       tively: any outstanding data modifications that would have been checked at the end of the transaction are instead checked
       during the execution of the SET CONSTRAINTS command.  If any such constraint is violated, the SET CONSTRAINTS 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. Triggers that are declared as ``constraint triggers'' are also affected.

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 foreign-key constraints.



SQL - Language Statements                                  2011-09-22                                         SET CONSTRAINTS(7)