How do foreign keys enforce referential integrity?

How do foreign keys enforce referential integrity?

• A. They require child values to match a parent table primary key; they can enforce cascading updates/deletes to maintain consistency.
• B. They create unique indexes on child table only.
• C. They require all tables to share the same primary key across the database.
• D. They provide audit trails for changes.

Answer: (A)

Referential integrity is about keeping related data in sync between tables. A foreign key enforces this by ensuring that every value in the child table’s foreign key column matches a value in the parent table’s primary (or unique) key. If you try to put a value in the child that doesn’t exist in the parent, the database blocks it, preventing orphaned records. It can also be set to cascade updates or deletes, so changes in the parent automatically propagate to the child, maintaining consistency across related rows. That’s why this option is the best: it captures both the matching requirement and the optional cascading behavior that helps preserve integrity. The other ideas don’t describe how foreign keys enforce referential integrity—foreign keys don’t inherently create unique indexes on the child, don’t require all tables to share the same primary key, and don’t provide audit trails.

Referential integrity is about keeping related data in sync between tables. A foreign key enforces this by ensuring that every value in the child table’s foreign key column matches a value in the parent table’s primary (or unique) key. If you try to put a value in the child that doesn’t exist in the parent, the database blocks it, preventing orphaned records. It can also be set to cascade updates or deletes, so changes in the parent automatically propagate to the child, maintaining consistency across related rows.

That’s why this option is the best: it captures both the matching requirement and the optional cascading behavior that helps preserve integrity. The other ideas don’t describe how foreign keys enforce referential integrity—foreign keys don’t inherently create unique indexes on the child, don’t require all tables to share the same primary key, and don’t provide audit trails.