Which constraint ensures that all values in a column are unique? MCQ with Answer and Explanation

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Which constraint ensures that all values in a column are unique?

A. CHECK

B. FOREIGN KEY

C. UNIQUE

D. PRIMARY KEY

Answer: Option C

Solution (By JKSSB Mock Tests)

UNIQUE constraint ensures that all values in a column are distinct, but allows NULL (unless combined with NOT NULL).

This question belongs to: Computer Database Management System (DBMS)

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Practice More Database Management System (DBMS) Questions

Question #1

In SQL, which clause is used to filter rows before grouping?

A. HAVING

B. GROUP BY

C. WHERE

D. ORDER BY

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Correct Answer: Option C

Explanation:
WHERE is used to filter individual rows before aggregation and grouping.

This question belongs to: Computer Database Management System (DBMS)

Question #2

In SQL, what does the wildcard '%' match when used with LIKE?

A. Only digits

B. A specific character

C. Any string of zero or more characters

D. Any single character

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Correct Answer: Option C

Explanation:
'%' matches any sequence of zero or more characters, while '_' matches a single character.

This question belongs to: Computer Database Management System (DBMS)

Question #3

Which normal form addresses partial dependencies, i.e., non-prime attributes dependent on part of a composite primary key?

A. 1NF

B. 3NF

C. 2NF

D. BCNF

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Correct Answer: Option C

Explanation:
Second Normal Form (2NF) eliminates partial dependencies by ensuring all non-key attributes are fully functionally dependent on the entire primary key.

This question belongs to: Computer Database Management System (DBMS)

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