GATE CSE 2014 Set 3 | Question: 22

Question

A prime attribute of a relation scheme $R$ is an attribute that appears

• A. in all candidate keys of $R$
• B. in some candidate key of $R$
• C. in a foreign key of $R$
• D. only in the primary key of $R$

Comments

in any candidate keys is correct..?

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A prime attribute is an attribute of any candidate key which may or may not be present in all candidate keys.

A prime attribute can be the part of one candidate key but may not be the part of other candidate key.

For ex: CKs = { A1, A2A3}, here, A1,A2,A3 are all prime attributes but all are not present in both keys.

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@Ravi_1511 yes

Answer 1

Answer (B).

The attributes of a candidate key are called the prime attributes. Suppose $ABC$ is one candidate key of a Relation $R(ABCDEFGH).$ Then the attributes $A, B$ and $C$ all are prime attributes. Similarly if $ABD$ is also another candidate key in the same relation $R,$ then $D$ is also a prime attribute. And conversely, an attribute that does not occur in ANY candidate key is called a non-prime attribute.

Answer 2

Prime attribute is a constituent of a candidate key. it need not present in all candidate keys. Hence, option B is correct.

Correct me if i went wrong.

Comments

Got it :)

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nice explanation satisfy with your explanation.

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Can Prime attribute be NULL in any of the the Candidate key ??

Can Prime attribute be NULL in Primary key ??

Answer 3

Answer is B

Answer 4

(A) in all candidate keys of $R$

a prime attribute need not be necessaryly in the primary key alone, though attributes in all the candidate key are considered prime attribute

Comments

it need not be  in all candidate keys of R