Use SET CONSTRAINTS command:
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 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.
You can also find that in the reference documentation of (for example) CREATE TABLE
[ CONSTRAINT constraint_name ]
{ NOT NULL |
NULL |
CHECK ( expression ) [ NO INHERIT ] |
DEFAULT default_expr |
GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ ( sequence_options ) ] |
UNIQUE index_parameters |
PRIMARY KEY index_parameters |
REFERENCES reftable [ ( refcolumn ) ] [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ]
[ ON DELETE action ] [ ON UPDATE action ] }
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
The constraint can be:
- INITIALLY DEFERRED | INITIALLY IMMEDIATE
- DEFERRABLE | NOT DEFERRABLE
