Which constraint ensures that a column cannot accept or store an unassigned or missing value? MCQ with Answer and Explanation

Which constraint ensures that a column cannot accept or store an unassigned or missing value?

A. CHECK

B. DEFAULT

C. UNIQUE

D. NOT NULL

Answer: Option D

The NOT NULL constraint explicitly forces a column to always contain a value, preventing blank or NULL entries.

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

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Question #1 Report Error

Who proposed the relational database model based on mathematical relation theory in 1970?

A. E.F. Codd

B. Charles Bachman

C. Dennis Ritchie

D. James Gosling

Correct Answer: Option A

Explanation:
Dr. Edgar Frank Codd (E.F. Codd) invented the relational model for database management while working for IBM in 1970.

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

Question #2 Report Error

Which SQL operator returns only the rows that are common and present in the outputs of both executing SELECT queries?

A. UNION

B. INTERSECT

C. EXCEPT / MINUS

D. JOIN

Correct Answer: Option B

Explanation:
The INTERSECT operator returns only the distinct rows that appear in the result sets of both SELECT statements.

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

Question #3 Report Error

What is the purpose of the SQL DISTINCT keyword?

A. To group the results

B. To filter rows based on a condition

C. To return only unique rows in the result set

D. To sort the result set

Correct Answer: Option C

Explanation:
DISTINCT removes duplicate rows from the query result.

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