Which method is commonly used to enforce referential integrity in a relational database?

• A. Use default values to preserve relationships
• B. Use column constraints to enforce relationship
• C. Use triggers to enforce relationships
• D. Use foreign key constraints that reference primary keys with on update/delete actions as needed

Answer: (D)

Referential integrity is about keeping relationships between tables consistent, so a row in a child table always points to an existing row in its parent table. The best and most common way to enforce this is with a foreign key constraint that links the child column(s) to the parent table’s primary key. This constraint is enforced by the database engine, preventing orphaned records automatically. You can also specify actions for updates or deletes, such as cascading changes or restricting them, to handle changes in the parent that would affect the child. This approach is reliable, declarative, and portable across systems.

Default values to preserve relationships aren’t a robust enforcement mechanism and don’t guarantee validity in all operations. Column constraints by themselves don’t express cross-table relationships. Triggers can enforce relationships but add complexity and potential maintenance issues, whereas foreign key constraints with appropriate on update/delete actions provide the standard, clean solution.