What is a self join? MCQ with Answer and Explanation

What is a self join?

A. Joining a table with itself

B. Joining more than two tables

C. Joining tables without a common column

D. Joining two different tables

Answer: Option A

A self join is a join where a table is joined with itself, often used to compare rows within the same table.

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

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Question #1 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. JOIN

D. EXCEPT / MINUS

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 #2 Report Error

What is a database cursor?

A. A type of index

B. A control structure that enables traversal over rows in a result set

C. A user account

D. A backup file

Correct Answer: Option B

Explanation:
A cursor allows row-by-row processing of query results, often used in procedural extensions of SQL.

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

Question #3 Report Error

Which constraint ensures that a column cannot have NULL values?

A. NOT NULL

B. UNIQUE

C. PRIMARY KEY

D. FOREIGN KEY

Correct Answer: Option A

Explanation:
NOT NULL constraint enforces that a column must have a value, preventing NULL entries.

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