Update violations for DELETE

A deletion operation may only violate Referential Integrity if the primary key value of the tuple being deleted is referenced from other tuples in the database.

We can remedy this by:

• RESTRICT: rejecting the deletion
• CASCADE: deleting referencing tuples This can be rather dangerous as it could delete big chunks of the database.
• SET NULL: set the $FK$ of the referencing tuples to $\text{null}$