What is the purpose of the SQL COALESCE function? MCQ with Answer and Explanation

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What is the purpose of the SQL COALESCE function?

A. Returns the first non-NULL value from a list

B. Computes the sum

C. Concatenates strings

D. Converts data types

Answer: Option A

Solution (By JKExamLibrary)

COALESCE returns the first non-NULL value among its arguments, often used to provide a default value.

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

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Question #1

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Which constraint ensures that every value in a specific column is unique across all rows in that table, but still permits a NULL value?

A. UNIQUE

B. PRIMARY KEY

C. FOREIGN KEY

D. CHECK

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Correct Answer: Option A

Explanation:
The UNIQUE constraint prevents duplicate entries in a column. Unlike a Primary Key, a UNIQUE constraint typically allows one or more rows to store NULL values depending on the database engine.

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

Question #2

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What is 'data about data' commonly referred to in a Database Management System?

A. Directory

B. Sub-data

C. Metadata

D. Hyper-data

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Correct Answer: Option C

Explanation:
Metadata is defined as data about data. It describes the structure, constraints, data types, and properties of the actual data stored in a database.

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