GATE CSE 2016 Set 1 | Question: 21

Question

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. $VXYZ$
• B. $VWXZ$
• C. $VWXY$
• D. $VWXYZ$

Answer 1

Any superset of a key is also a superkey from definition of a superkey.
So, answer is B.

a superkey can be defined as a set of attributes of a relation schema upon which all attributes of the schema are functionally dependent

Comments

the primary key is  {V,Y} this should be present in all superkey...check in all option in option B ..{V,Y} is not present hence this should be answer.

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check the above answer by chalam121 on Mar 26, 2018. He has explained the same thing.

Bro no one is benefited by repeating answers. It unnecessarily adds to redundancy. Hope you get it :)

Answer 2

Here Primary Key IS VY

 

If its SuperKey Any Key It Should  Must Contains VY as Part of it

Option A  VXYZ     So VY is Part of it    Correct

Option B  VWXZ    SO No VY is Subset It Faills It Incorrect

Option  C  VWXY  So VY is Part o f it    Correct

Option D  VWXYZ  So VY is Part of it    it Also  Correct

Answer Is B