Which statement about foreign keys is accurate?

• A. A foreign key references a primary key (or a candidate key) in another table.
• B. A foreign key must reference a non-key attribute.
• C. A foreign key is the same as a primary key.
• D. A foreign key cannot be null.

Answer: (A)

A foreign key is a field (or set of fields) in one table that points to a row in another table, typically by referencing the primary key of that table. This linkage enforces referential integrity: the value in the foreign key must match an existing value in the referenced key, so you can’t have orphaned records. Because the referenced key is usually the primary key or another candidate key (a uniquely identifying key), the statement that a foreign key references a primary key or a candidate key in another table is correct. It isn’t about referencing a non-key attribute; it must point to a key that uniquely identifies a row. A foreign key is distinct from a primary key, serving as a pointer rather than the table’s unique identifier. Also, foreign keys can be null if the relationship is optional, so the prohibition on nulls isn’t universally true.