What does the Delete Restrict rule prevent?

What does the Delete Restrict rule prevent?

• A. It prevents updating a primary key value that is referenced by a foreign key.
• B. It prevents deleting a row if its primary key is referenced by a foreign key.
• C. It prevents inserting a row with a null foreign key value.
• D. It prevents deleting a row that has no referencing foreign keys.

Answer: (B)

Delete Restrict focuses on keeping references intact. It prevents removing a row from the parent table if other tables still have rows that point to it via a foreign key. If there are any child rows that reference this row’s primary key, the delete is blocked to avoid orphaned references. Only when there are no references can the row be deleted. For example, if a row in a Customers table is referenced by rows in an Orders table, that customer cannot be deleted until those orders are removed or updated to refer elsewhere. This isn’t about updating a primary key, inserting a null foreign key, or deleting a row that has no references (the last would be allowed).

Delete Restrict focuses on keeping references intact. It prevents removing a row from the parent table if other tables still have rows that point to it via a foreign key. If there are any child rows that reference this row’s primary key, the delete is blocked to avoid orphaned references. Only when there are no references can the row be deleted. For example, if a row in a Customers table is referenced by rows in an Orders table, that customer cannot be deleted until those orders are removed or updated to refer elsewhere. This isn’t about updating a primary key, inserting a null foreign key, or deleting a row that has no references (the last would be allowed).