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MySQL MCQ With Answers

41 practice questions · Last updated on Aug 25, 2026

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MySQL interviews focus on whether you understand what the database is actually doing. Expect questions on InnoDB versus MyISAM, how B-tree indexes work and when they are ignored, transaction isolation levels, join semantics, replication, and reading EXPLAIN output to tune a slow query. Employers also probe operational judgement: how you handle deadlocks, how you run a migration on a large table, and how you choose data types. The questions below cover both the theory and the practical decisions.

MySQL MCQ

1.Which storage engine is the default in MySQL since version 5.5?

3.What is the default transaction isolation level in InnoDB?

5.Which clause filters rows AFTER aggregation has been performed?

7.Which index does InnoDB use to physically store the table rows?

8.Given a composite index on (a, b, c), which query can use the index?

9.Why can an index on created_at not be used by WHERE YEAR(created_at) = 2024?

10.What is the difference between CHAR and VARCHAR?

12.What does the ACID acronym stand for in database transactions?

13.Which statement adds a new column to an existing table?

14.What does a FOREIGN KEY constraint enforce?

16.What happens when InnoDB detects a deadlock?

17.Which command shows the currently running queries on a MySQL server?

18.What is a covering index?

20.What does the LIMIT clause do?

21.Which normal form requires that no non-key column depends on another non-key column?

22.What is the purpose of the UNION operator?

23.Which statement about NULL in MySQL is correct?

24.What is the main advantage of a prepared statement?

25.In MySQL replication, what does the replica's I/O thread do?

26.Which of these will make a query unable to use an index on a VARCHAR column?

27.What is the difference between a stored procedure and a function in MySQL?

28.What does the AUTO_INCREMENT attribute do?

29.Which command creates a backup of a MySQL database as SQL statements?

30.What does the GROUP BY clause do?

31.Which isolation level allows dirty reads?

32.What is the purpose of the InnoDB buffer pool?

33.Which statement correctly grants SELECT permission on one database to a user?

34.What does the DISTINCT keyword do?

35.What is a view in MySQL?

36.Which of these best reduces the size of a large InnoDB table's file after deleting many rows?

37.What does the ON DELETE CASCADE option on a foreign key do?

38.Which clause is used to sort query results?

39.What does 'Using filesort' in EXPLAIN Extra indicate?

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

41.Which approach best prevents SQL injection in an application using MySQL?

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