A Primary Key in RDBMS must be: MCQ with Answer and Explanation

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A Primary Key in RDBMS must be:

A. Duplicate values allowed

B. Unique and not null

C. Always a foreign key

D. Can have null values

Answer: Option B

Solution (By JKSSB Mock Tests)

A primary key uniquely identifies each record and cannot contain null values.

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

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Practice More Database Management System (DBMS) Questions

Question #1

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

A. Any string of zero or more characters

B. Only digits

C. A specific character

D. Any single character

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Correct Answer: Option A

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

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

Question #2

Which of the following is NOT an aggregate function in standard SQL?

A. AVG()

B. LENGTH()

C. COUNT()

D. SUM()

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Correct Answer: Option B

Explanation:
SUM(), AVG(), and COUNT() are aggregate functions operating on multiple rows, whereas LENGTH() is a scalar function acting on a single text value.

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

Question #3

What is a subquery in database terminology?

A. A query that executes after the main query terminates.

B. A nested SQL query placed completely inside another outer query statement.

C. An error log file.

D. A query that runs on a backup server.

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Correct Answer: Option B

Explanation:
A subquery (or nested query) is an inner SQL SELECT statement embedded within an outer statement (such as a WHERE, FROM, or SELECT clause).

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

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