UGC NET CSE | December 2015 | Part 3 | Question: 59

Question

Consider the following database table:

Create table test(
    one integer,
    two integer,
    primary key(one),
    unique(two),
    check(one>=1 and <=10),
    check (two>=1 and <=5)
    );

How many data records/tuples atmost can this table contain?

• A. $5$
• B. $10$
• C. $15$
• D. $50$

Comments

You are right. If values of some attribute are constrained to take only unique values, it is still allowed to take Null value. And more importantly it can take null value mltiple time, since in most of the SQL engine null is not equal to null. 

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10 is correct.

Answer 1

B. 10 should be the correct answer.

Reason : As one is primary key and it varies from 1 to 10 , So using one atmost 10 tuples can be there. When we take two into consideration it varies from 1 to 5 and is unique, which implies it can be NULL. Hence the number of tuples will be 10, with two being NULL in five of them.

CORRECT ME IF I AM WRONG.

Comments

I have a Question:  What if 1 to 5 which is Unique is not NULL ? (As in the question it is asked "Atmost")

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You are right unique can contain NULL values, but what about  check (two>=1 and <=5) this condition? if this condition fails the new tuple will not be created, so I think answer should be A)5