Question

What is a foreign key?

(a) A foreign key is a primary key of a relation which is an attribute in another relation

(b) A foreign key is a superkey of a relation which is an attribute in more than one other relations

(c) A foreign key is an attribute of a relation that is a primary key of another relation

(d) A foreign key is the primary key of a relation that does not occur anywhere else in the schema

This question was posed to me in a job interview.

Origin of the question is Introduction to the Relational Model in portion Introduction to Relational Model and Sql of RDBMS

Answer 1

Correct answer is (c) A foreign key is an attribute of a relation that is a primary key of another relation

The explanation is: A foreign key is an attribute of a relation that is initially a primary key of another relation. A foreign key usage preserves referential integrity.