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A relation $R(P,Q,R,S)$ has $\{PQ, QR, RS, PS\}$ as candidate keys. The total number of superkeys possible for relation $R$ is ______
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Number of Superkeys which are superset of PQ = 2^2 = 4

Number of Superkeys which are superset of QR = 2^2 = 4

Number of Superkeys which are superset of PS = 2^2 = 4

Number of Superkeys which are superset of RS = 2^2 = 4

Number of Superkeys which are superset of PQR = 2^1 = 2

Number of Superkeys which are superset of PQS = 2^1 =2

Number of Superkeys which are superset of PRS = 2^1 =2

Number of Superkeys which are superset of QRS = 2^1 = 2

Number of Superkeys which are superset of PQRS = 2^0 = 1

 

So, applying the formula of Set theory, the total number of Superkeys possible on given relation are = 4+4+4+4-2-2-2-2+1 = 9
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