SET CONSTRAINTS(7)	PostgreSQL 9.2.24 Documentation	    SET CONSTRAINTS(7)



NAME
       SET_CONSTRAINTS - set constraint check timing 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). Each constraint
       name can be schema-qualified. 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
       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 UNIQUE, PRIMARY KEY, REFERENCES (foreign key), and
       EXCLUDE constraints are affected by this setting.  NOT NULL and CHECK
       constraints are always checked immediately when a row is inserted or
       modified (not at the end of the statement). Uniqueness and exclusion
       constraints that have not been declared DEFERRABLE are also checked
       immediately.

       The firing of triggers that are declared as "constraint triggers" is
       also controlled by this setting -- they fire at the same time that the
       associated constraint should be checked.

NOTES
       Because PostgreSQL does not require constraint names to be unique
       within a schema (but only per-table), it is possible that there is more
       than one match for a specified constraint name. In this case SET
       CONSTRAINTS will act on all matches. For a non-schema-qualified name,
       once a match or matches have been found in some schema in the search
       path, schemas appearing later in the path are not searched.

       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 does not apply to NOT
       NULL and CHECK constraints. Also, PostgreSQL checks non-deferrable
       uniqueness constraints immediately, not at end of statement as the
       standard would suggest.



PostgreSQL 9.2.24		  2017-11-06		    SET CONSTRAINTS(7)