GATE CS 2016 Set 1 — Question 31
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Databases → Relational Model → Keys (Super, Candidate, Foreign)
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Question
Which of the following is NOT a superkey in a relational schema with attributes and primary key ?
Correct answer
(B) VWXZ
Solution
A superkey is a set of attributes within a table whose values can be used to uniquely identify a tuple. A superkey is a superset of a candidate key.Given:
- Attributes:
- Primary Key (Candidate Key):
- (A) : Contains and . It is a superkey.
- (B) : Contains but does not contain . Since it does not contain the primary key , and no other functional dependencies are given to imply another key, it is not a superkey.
- (C) : Contains and . It is a superkey.
- (D) : Contains and . It is a superkey (trivial superkey).
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