What is referential integrity?

• A. Referential integrity ensures that a foreign key value always matches an existing primary key value (or is null if allowed).
• B. Referential integrity prevents a table from having more than one column.
• C. Referential integrity guarantees all attributes are derived.
• D. Referential integrity enforces that every table has a primary key.

Answer: (A)

Referential integrity ensures that relationships between tables stay consistent by enforcing that a foreign key value must correspond to a valid value in the related table’s primary key, or be NULL if the relationship allows it. This keeps data linked correctly and prevents references to non-existent records. For example, an orders row with a customer_id must refer to an existing customer in the customers table, so the customer_id must match an existing customers.id value (or be NULL if the design allows that). The other statements describe different database ideas: one talks about limiting how many columns a table can have, another about attributes being derived, and the last about every table having a primary key—none of which describe referential integrity.