Answer:
By definition a foreign key of table A is a primary key of another table B, thereby establishing a link between them.
To provide referential integrity you can use these referential actions:
- Cascade: If rows in table B are deleted, the matching foreign key columns in table A are deleted.
- Set Null: If rows in table B are deleted, the matching foreign key columns in table A are set to null.
- Set Default: If rows in table B are deleted, the matching foreign key columns in table A are set with the default value of the column.
- Restrict: A value in table B cannot be deleted or updated while as it is referred to by a foreign key in table A.
