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

GATE 2016 · Databases · Database Normalization · easy

Answer: VWXZ is NOT a superkey — option D.

1. Identify the condition for a superkey: Primary key = {V, Y}. A set S is a superkey iff {V,Y} ⊆ S, i.e., both V and Y appear in S.
2. Check each option: A. {V,Y,Z}: contains V? Yes. contains Y? Yes. => Superkey. B. {V,W,X,Y}: contains V? Yes. contains Y? Yes. => Superkey. C. {V,W,Y}: contains V? Yes. contains Y? Yes. => Superkey. D. {V,W,X,Z}: contains V? Yes. contains Y? NO. => NOT a superkey.