The delete and update rules that you specify when you create a constraint apply to parent key changes. The database enforces a no-action rule on the insert and update operations to the foreign key in order to maintain referential integrity. The system enforces this rule on the insert and update operations to the foreign key to ensure that the value of every non-null foreign key matches the value of the parent key.
The system returns a referential constraint violation if a matching parent key does not exist for the new foreign key value, and does not insert or update the dependent record.