Thus, SET CONSTRAINTS can be used to force checking of constraints to occur at a specific point in a transaction.Ĭurrently, only UNIQUE, PRIMARY KEY, REFERENCES (foreign key), and EXCLUDE constraints are affected by this setting. If any such constraint is violated, the SET CONSTRAINTS fails (and does not change the constraint mode). 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. SET CONSTRAINTS ALL changes the mode of all deferrable constraints. The current schema search path is used to find the first matching name if no schema name is specified. Each constraint name can be schema-qualified. SET CONSTRAINTS with a list of constraint names changes the mode of just those constraints (which must all be deferrable). The first two classes start every transaction in the indicated mode, but their behavior can be changed within a transaction by SET CONSTRAINTS. The third class is always IMMEDIATE and is not affected by the SET CONSTRAINTS command. Upon creation, a constraint is given one of three characteristics: DEFERRABLE INITIALLY DEFERRED, DEFERRABLE INITIALLY IMMEDIATE, or NOT DEFERRABLE. Each constraint has its own IMMEDIATE or DEFERRED mode. DEFERRED constraints are not checked until transaction commit.

IMMEDIATE constraints are checked at the end of each statement. SET CONSTRAINTS sets the behavior of constraint checking within the current transaction.

Postgres add constraint