SET CONSTRAINTS
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 ownIMMEDIATE orDEFERRED mode.
Upon creation, a constraint is given one of three characteristics:DEFERRABLE INITIALLY DEFERRED,DEFERRABLE INITIALLY IMMEDIATE, orNOT DEFERRABLE. The third class is alwaysIMMEDIATE and is not affected by theSET CONSTRAINTS command. The first two classes start every transaction in the indicated mode, but their behavior can be changed within a transaction bySET 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.
WhenSET CONSTRAINTS changes the mode of a constraint fromDEFERRED toIMMEDIATE, 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 theSET CONSTRAINTS command. If any such constraint is violated, theSET 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, onlyUNIQUE,PRIMARY KEY,REFERENCES (foreign key), andEXCLUDE constraints are affected by this setting.NOT NULL andCHECK 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 declaredDEFERRABLE 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
BecausePostgres Pro 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 caseSET 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. Issuing this outside of a transaction block emits a warning and otherwise has no effect.
Compatibility
This command complies with the behavior defined in the SQL standard, except for the limitation that, inPostgres Pro, it does not apply toNOT NULL andCHECK constraints. Also,Postgres Pro checks non-deferrable uniqueness constraints immediately, not at end of statement as the standard would suggest.