Question

If a1, a2, a3 are attributes in a relation and S is another relation, which of the following is an incorrect specification of an integrity constraint?

(a) primary key(a1, a2, a3)

(b) primary key(a1)

(c) foreign key(a1, a2) references S

(d) foreign key(a1, a2)

This question was addressed to me during an interview.

I want to ask this question from SQL Data definition in chapter Introduction to Relational Model and Sql of RDBMS

Answer 1

Right answer is (d) foreign key(a1, a2)

Explanation: Whenever the integrity constraint foreign key is mentioned, the attributes that are the foreign keys should always be referenced from the relation in which they are primary keys.