The GATE Grind

GATE 2016 CS – Question 31

Databases · Integrity Constraints and Normal Forms · 1 mark · Multiple choice

Which of the following is NOT a superkey in a relational schema with attributes $V, W, X, Y, Z$ and primary key $VY$?

  1. $VXYZ$
  2. $VWXZ$
  3. $VWXY$
  4. $VWXYZ$

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Show answer and explanation

Correct answer: (B) $VWXZ$

Explanation

A superkey must contain a candidate key, so here it must include both $V$ and $Y$. Options A, C and D contain $VY$. Option $VWXZ$ is missing $Y$, so it is not a superkey.