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.