set_constraints man page on aLinux

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

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

       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.  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). If there are
       multiple constraints matching any given name, all  are  affected.   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.

       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.

       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.

       The  SQL	 standard  says	 that  constraint  names appearing in SET CON‐
       STRAINTS can be schema-qualified. This is not yet  supported  by	 Post‐
       greSQL: the names must be unqualified, and all constraints matching the
       command will be affected no matter which schema they are in.

SQL - Language Statements	  2005-11-05		     SET CONSTRAINTS()

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