What is a foreign key?

• A. An attribute that uniquely identifies a row within the same table.
• B. An attribute that creates a link to a primary key in another table.
• C. An attribute that ensures uniqueness of values in the same column.
• D. An attribute that stores derived data.

Answer: (B)

A foreign key is a link that ties two tables together. It is an attribute (or a set of attributes) in one table that points to the primary key (or another unique key) in another table, establishing a relationship between the two tables. This link enforces referential integrity, meaning every value in the foreign key must correspond to a valid row in the related table. Because of this connection, you can join the tables in queries and keep related data consistently connected. The other descriptions refer to different concepts: the attribute that uniquely identifies a row in the same table is a primary key; the attribute that ensures uniqueness in a column is a unique key or constraint; and storing derived data describes computed attributes, not a linking mechanism between tables.