Computer Sciences > GATE 2026 SET-1 > Keys and Normalization
A relation R(ABCD) has only two candidate keys AB and AC. What is the number of super keys?
Correct : 6
A super key is any superset of a candidate key.
Candidate keys are: AB and AC
Remaining attributes (not in both candidate keys) = D
Super keys from candidate key AB:
AB can be extended with any subset of {D}
AB, ABD → 2 super keys
Super keys from candidate key AC:
AC can be extended with any subset of {D}
AC, ACD → 2 super keys
Super keys from candidate key ABC (AB + C):
ABC, ABCD → 2 super keys
Total super keys = AB, ABD, AC, ACD, ABC, ABCD = 6
Note: ABCD is counted only once even though it is a superset of both AB and AC.
∴ The number of super keys = 6
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