Which statement about primary keys in a relational database table is completely true? MCQ with Answer and Explanation

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Which statement about primary keys in a relational database table is completely true?

A. A table can have multiple distinct primary keys.

B. A table can contain at most one primary key.

C. A primary key column can accept a single NULL value.

D. Primary keys must always be numeric integers.

Answer: Option B

Solution (By JKSSB Mock Tests)

A relational database table can have exactly one primary key constraint defined, which uniquely identifies each record and strictly forbids NULLs.

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

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Question #1

In SQL, what is the purpose of the LIKE operator?

A. To perform pattern matching on strings

B. To aggregate data

C. To join tables

D. To perform arithmetic operations

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Correct Answer: Option A

Explanation:
LIKE is used with wildcards (% and _) to search for a specified pattern in a column.

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

Question #2

Which SQL command is used to permanently remove an entire table structure along with all its data from the database?

A. REMOVE

B. DROP

C. TRUNCATE

D. DELETE

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Correct Answer: Option B

Explanation:
The DROP command is a DDL statement that completely removes a table's structure, definition, and all its associated data from the database.

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

Question #3

What is the result of the SQL query: SELECT * FROM employees;?

A. Only the first row

B. All rows and all columns from the employees table

C. An empty result

D. Only the primary key column

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Correct Answer: Option B

Explanation:
SELECT * retrieves all columns and rows from the specified table.

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

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