SET CONSTRAINTS
SQL - Language Statements
SET CONSTRAINTS
set constraint checking modes for the current transaction
SET CONSTRAINTS
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: INITIALLY DEFERRED,
INITIALLY IMMEDIATE DEFERRABLE, or
INITIALLY IMMEDIATE NOT DEFERRABLE. The third
class 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). If
there are multiple constraints matching any given name, all are affected.
SET CONSTRAINTS ALL changes the mode of all deferrable
constraints.
When you change 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).
Currently, only foreign key constraints are affected by this
setting. Check and unique constraints are always effectively
initially immediate not deferrable.
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. If you wish to change the behavior
of a constraint without needing to issue a SET
CONSTRAINTS command in every transaction, specify
INITIALLY DEFERRED or INITIALLY
IMMEDIATE when you create the constraint.
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.
The SQL standard says that constraint names appearing in SET
CONSTRAINTS can be schema-qualified. This is not yet
supported by PostgreSQL: the names must
be unqualified, and all constraints matching the command will be
affected no matter which schema they are in.