Immediate and Deferred Integrity Constraints

In some situations, we do not want integrity constraints to be checked immediately, that
is after every SQL statement has been executed, but instead at transaction commit. A
constraint may be defined as INITIALLY IMMEDIATE or INITIALLY DEFERRED,
indicating which mode the constraint assumes at the start of each transaction. In the
former case, it is also possible to specify whether the mode can be changed subsequently
using the qualifier [NOT] DEFERRABLE. The default mode is INITIALLY
IMMEDIATE.
The SET CONSTRAINTS statement is used to set the mode for specified constraints for
the current transaction. The format of this statement is:
SET CONSTRAINTS
{ALL | constraintName [, . . . ]} {DEFERRED | IMMEDIATE}