UGC NET CSE | December 2007 | Part 2 | Question: 16

Question

A primary key for an entity is :

• A. a candidate key

• B. any attribute

• C. a unique attribute

• D. a superkey

Answer 1

Option B) is surely wrong.

Option D) you can discard, because in the option candidate keys is there, which is a minimal set of super key.(https://dba.stackexchange.com/questions/71924/what-is-the-difference-between-primary-key-and-super-key-in-dbms)

Now in option (A) and (C), I will choose Option A, because one of the most important properties of Primary key is that it should not have NULL value. But in Option C it can not be guarantee.

Hence I will choose Option (A) as answer.

• The primary key of a relation is a candidate key especially selected to be the key for the relation.
• In other words, it is a choice, and there can be only one candidate key designated to be the primary key.