Which of the following is NOT a superkey in a relational schema with…
2016
Which of the following is NOT a superkey in a relational schema with attributes V, W, X, Y, Z and primary key V Y?
- A.
V X Y Z
- B.
V W X Z
- C.
V W X Y
- D.
V W X Y Z
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Correct answer: B
Key idea: because V and Y form the primary key, any superkey must contain both V and Y (or otherwise functionally determine them).
V W X Z does not include Y, so it cannot uniquely identify tuples and is not a superkey.
Each of the other sets (V X Y Z, V W X Y, V W X Y Z) contains both V and Y, so they are superkeys (they include the primary key).
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