How does a relational database enforce referential integrity?

How does a relational database enforce referential integrity?

• A. With triggers only.
• B. By duplicating all data across tables.
• C. Through user IDs.
• D. With foreign keys that enforce referential constraints.

Answer: (D)

Referential integrity in a relational database is enforced through foreign key constraints. A foreign key in a child table points to a primary (or unique) key in a parent table, and the database ensures that every non-null value in the foreign key exists in the referenced column. This prevents "orphan" references and keeps related data consistent. The constraint can also specify actions for updates or deletes on the parent, such as cascading changes, setting the child foreign key to null, or restricting the operation. Triggers can be used to enforce rules, but foreign keys provide a built-in, declarative way to maintain this integrity and are generally the standard mechanism. Duplicating data across tables undermines normalization and isn’t how referential integrity is guaranteed. Merely using user IDs without a formal constraint doesn’t enforce the relationship either.

Referential integrity in a relational database is enforced through foreign key constraints. A foreign key in a child table points to a primary (or unique) key in a parent table, and the database ensures that every non-null value in the foreign key exists in the referenced column. This prevents "orphan" references and keeps related data consistent. The constraint can also specify actions for updates or deletes on the parent, such as cascading changes, setting the child foreign key to null, or restricting the operation.

Triggers can be used to enforce rules, but foreign keys provide a built-in, declarative way to maintain this integrity and are generally the standard mechanism. Duplicating data across tables undermines normalization and isn’t how referential integrity is guaranteed. Merely using user IDs without a formal constraint doesn’t enforce the relationship either.