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A foreign key is which of the following?

  • A.Any attribute
  • B.The same thing as a primary key
  • C.An attribute that serves as the primary key of another relation
  • D.An attribute that serves no purpose

Answer: C

Correct answer: An attribute that serves as the primary key of another relation

A foreign key is how relations are joined: it holds the value of some other relation’s primary key, and referential integrity requires that value either to exist there or to be null. It may be part of its own relation’s primary key too, as in an associative relation.

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