1.

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)

Answer» 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.


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