SQL Quiz Test Online (30 random Questions) 2026

This quick 30-minute challenge consists of 30 random multiple-choice questions designed to test your knowledge across various SQL topics, including the introduction to databases, data manipulation and querying, database design and normalization, advanced SQL concepts, and database administration and security. Whether you’re a beginner or looking to expand your SQL expertise, this quiz will enhance your understanding of database management and querying skills.

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30 Minutes SQL Quiz Test Online

Welcome to the SQL Quiz! This quick 30-minute challenge consists of 30 random multiple-choice questions designed to test your knowledge across various SQL topics, including the introduction to databases, data manipulation and querying, database design and normalization, advanced SQL concepts, and database administration and security. Whether you're a beginner or looking to expand your SQL expertise, this quiz will enhance your understanding of database management and querying skills.

1 / 30

1. What is the purpose of the WHERE clause in SQL?

A) To filter records

B) To sort data

C) To join tables

D) To create indexes

2 / 30

2. Which command is used to modify existing rows in a table?

A) MODIFY

B) INSERT

C) ALTER

D) UPDATE

3 / 30

3. How do you rename a column in the result set?

A) ALIAS

B) AS

C) RENAME

D) USING

4 / 30

4. Which of the following is not a type of SQL join?

A) OUTER JOIN

B) INNER JOIN

C) CROSS JOIN

D) FULL JOIN

5 / 30

5. What is the primary purpose of a database schema?

A) To define the structure of the database

B) To execute SQL queries

C) To store backup files

D) To grant user permissions

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6. How do you retrieve unique values from a column?

A) DISTINCT

B) FILTER

C) GROUP BY

D) UNIQUE

7 / 30

7. What does the LIKE operator do?

A) Deletes records

B) Sorts data

C) Matches a pattern in a string

D) Joins tables

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8. How can user activity be restricted during maintenance?

A) By shutting down the database

B) By locking the database

C) By switching to read-only mode

D) By revoking all permissions

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9. Which of the following is a type of SQL statement?

A) All of the above

B) Data Manipulation Language (DML)

C) Data Control Language (DCL)

D) Data Definition Language (DDL)

10 / 30

10. What is normalization in databases?

A) Adding redundancy

B) Increasing database size

C) Simplifying queries

D) Removing redundant data

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11. How does the SQL MERGE statement work?

A) Optimizes indexes for faster retrieval

B) Combines columns from two queries into one result set

C) Performs insert, update, or delete operations based on a condition

D) Merges two tables into one new table

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12. What is the purpose of the UNION operator?

A) Deletes records

B) Joins tables

C) Filters duplicate rows

D) Combines results of two queries

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13. What is the purpose of indexing in SQL?

A) To increase redundancy

B) To speed up queries

C) To normalize tables

D) To reduce redundancy

14 / 30

14. What is the first step in database normalization?

A) Eliminating redundant data

B) Ensuring all columns are atomic

C) Adding composite keys

D) Removing foreign keys

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15. What is the result of normalization up to BCNF?

A) Optimizes performance for all queries

B) Completely eliminates redundancy

C) Ensures every determinant is a candidate key

D) Allows multivalued attributes

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16. What is the main difference between a UNION and a UNION ALL?

A) UNION is faster than UNION ALL

B) UNION removes duplicates; UNION ALL does not

C) UNION merges columns; UNION ALL merges rows

D) UNION ALL removes duplicates; UNION does not

17 / 30

17. Which keyword is used to match patterns in SQL?

A) MATCH

B) LIKE

C) PATTERN

D) SEARCH

18 / 30

18. How does database mirroring enhance security?

A) By preventing SQL injection

B) By auditing user activities

C) By encrypting data

D) By replicating data to a standby server

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19. What does the term 'role-based access control' (RBAC) mean?

A) Backing up the database

B) Granting access based on predefined roles

C) Assigning permissions to individual users

D) Encrypting sensitive data

20 / 30

20. What is denormalization?

A) Eliminating all keys from a table

B) Normalizing a database to BCNF

C) Breaking tables into smaller parts

D) Combining tables to improve performance

21 / 30

21. Which of the following best describes a self-join?

A) A join that merges columns

B) A join between two different tables

C) A join of a table with itself

D) A join that excludes null values

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22. What is the result of a CROSS JOIN?

A) Intersection of two tables

B) Cartesian product of two tables

C) Difference of two tables

D) Union of two tables

23 / 30

23. What is a window function in SQL?

A) A function that operates on a subset of rows

B) A function that partitions data for analysis

C) All of the above

D) A function that performs calculations across a window of rows

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24. How does the LAG() function work in SQL?

A) Returns the average value of a set

B) Returns the previous value in a set

C) Returns the next value in a set

D) Computes a running total

25 / 30

25. How do you sort query results?

A) ORDER BY

B) FILTER

C) SORT BY

D) GROUP BY

26 / 30

26. What is the key benefit of schema normalization in large databases?

A) Simplifies data visualization

B) Reduces storage requirements and improves data consistency

C) Ensures better data visualization

D) Eliminates indexing needs

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27. What happens if a table is not normalized?

A) Improved performance

B) Increased redundancy and anomalies

C) Elimination of relationships

D) Reduced storage usage

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28. What does BCNF stand for?

A) Binary Conjugate Normal Form

B) None of the above

C) Basic Composite Normal Form

D) Boyce-Codd Normal Form

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29. What does the term 'two-factor authentication' (2FA) mean?

A) Using two levels of encryption

B) Authenticating two users simultaneously

C) Using two databases for authentication

D) Verifying identity with two methods (e.g., password and OTP)

30 / 30

30. Which operator is used to combine the results of two queries?

A) JOIN

B) CONNECT

C) UNION

D) MERGE

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