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. PRIMARY KEY

B. FOREIGN KEY

C. UNIQUE

D. CHECK

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

What is the purpose of a Foreign Key?

A. To sort data

B. To uniquely identify records

C. To create indexes

D. To link two tables and enforce referential integrity

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Correct Answer: Option D

Explanation:
A foreign key establishes a relationship between tables and maintains referential integrity.

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

Question #2

Which SQL clause is used to filter groups after grouping?

A. WHERE

B. GROUP BY

C. HAVING

D. ORDER BY

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Correct Answer: Option C

Explanation:
HAVING is used to filter groups based on aggregate conditions, applied after GROUP BY.

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

Question #3

Which wildcard character is used with the SQL LIKE operator to represent zero, one, or multiple characters?

A. Percentage sign (%)

B. Ampersand (&)

C. Hash (#)

D. Underscore (_)

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Correct Answer: Option A

Explanation:
The percentage sign (%) is used as a wildcard character to match any sequence of zero or more characters in an SQL LIKE string comparison query.

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

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