What is the difference between a primary key and a unique key? MCQ with Answer and Explanation

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What is the difference between a primary key and a unique key?

A. Primary key cannot have NULL; unique key can have one NULL (in most DBMS)

B. Primary key is always integer; unique key can be any data type

C. Unique key is always a foreign key

D. There is no difference

Answer: Option A

Solution (By JKExamLibrary)

A primary key is a unique identifier that cannot be NULL, while a unique key allows NULL values (usually one) and can be used for alternate keys.

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

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Practice More Database Management System (DBMS) Questions

Question #1

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When the same data is updated in one location but remains unchanged in another location, it creates a state of what?

A. Data Integrity

B. Data Inconsistency

C. Data Security

D. Data Independence

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Correct Answer: Option B

Explanation:
Data Inconsistency occurs when different versions of the same data appear in different places due to uncontrolled data redundancy.

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

Question #2

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Which operator is used to combine the distinct result sets of two or more SELECT queries into a single output, automatically filtering out duplicate rows?

A. UNION

B. UNION ALL

C. EXCEPT

D. INTERSECT

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Correct Answer: Option A

Explanation:
The UNION operator merges the result sets of two queries, removing any duplicate records. UNION ALL performs a similar merge but retains duplicates.

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