NAME
SET CONSTRAINTS - set constraint checking modes 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). 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 foreign key constraints are affected by this setting.
Check and unique constraints are always effectively not deferrable.
Triggers that are declared as ‘‘constraint triggers’’ are also
affected.
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.
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.