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. Converts data types

C. Computes the sum

D. Concatenates strings

Answer: Option A

Solution (By JKSSB Mock Tests)

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

Which of the following is a valid SQL statement to add a new column to a table?

A. ADD COLUMN TO table_name column_name datatype;

B. ALTER TABLE table_name ADD COLUMN column_name datatype;

C. ALTER TABLE table_name ADD column_name datatype;

D. Both A and C

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Correct Answer: Option D

Explanation:
Both 'ADD column_name datatype' and 'ADD COLUMN column_name datatype' are valid syntax in some DBMS, but standard SQL uses 'ADD column_name datatype'. However, many DBMS support both.

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

Question #2

What does DDL stand for in SQL?

A. Data Manipulation Language

B. Dynamic Data Link

C. Data Description Language

D. Data Definition Language

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Correct Answer: Option D

Explanation:
DDL (Data Definition Language) includes commands like CREATE, ALTER, DROP for defining database structures.

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

Question #3

Which SQL command is used to reverse or undo all modifications made during the current transaction that have not yet been committed?

A. UNDO

B. SAVEPOINT

C. ROLLBACK

D. REVERT

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Correct Answer: Option C

Explanation:
The ROLLBACK command is a TCL statement used to undo transactions, restoring the database to its last committed or safe state.

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

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