SET 
CONSTRAINTS(7)					  PostgreSQL 9.2.7 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 9.2.7						    2014-02-17							SET CONSTRAINTS(7)