Editing Foreign key (section)

=== NO ACTION ===
NO ACTION and RESTRICT are very much alike. The main difference between NO ACTION and RESTRICT is that with NO ACTION the referential integrity check is done after trying to alter the table. RESTRICT does the check before trying to execute the [[update (SQL)|UPDATE]] or [[delete (SQL)|DELETE]] statement. Both referential actions act the same if the referential integrity check fails: the UPDATE or DELETE statement will result in an error.

In other words, when an UPDATE or DELETE statement is executed on the referenced table using the referential action NO ACTION, the DBMS verifies at the end of the statement execution that none of the referential relationships are violated. This is different from RESTRICT, which assumes at the outset that the operation will violate the constraint. Using NO ACTION, the [[Database trigger|triggers]] or the semantics of the statement itself may yield an end state in which no foreign key relationships are violated by the time the constraint is finally checked, thus allowing the statement to complete successfully.