SQL Quiz Test Online (30 random Questions) 2025

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 main difference between a UNION and a UNION ALL?

A) UNION merges columns; UNION ALL merges rows

B) UNION is faster than UNION ALL

C) UNION ALL removes duplicates; UNION does not

D) UNION removes duplicates; UNION ALL does not

2 / 30

2. What is a composite key?

A) A primary key consisting of multiple columns

B) A key used for indexing

C) A temporary key

D) A foreign key with a single column

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3. What is the main drawback of normalization?

A) Increases redundancy

B) Slower write operations due to more joins

C) Reduces database size

D) Reduces data integrity

4 / 30

4. Which SQL keyword is used to combine results from multiple queries?

A) INTERSECT

B) EXCEPT

C) JOIN

D) UNION

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

A) Optimizes performance for all queries

B) Allows multivalued attributes

C) Completely eliminates redundancy

D) Ensures every determinant is a candidate key

6 / 30

6. How do you add a new column to an existing table?

A) UPDATE TABLE

B) ALTER TABLE

C) ADD COLUMN

D) INSERT COLUMN

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7. What is a scalar subquery?

A) A subquery that returns multiple rows

B) A subquery that returns a single value

C) A subquery that updates data

D) A subquery used in joins

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

A) ALIAS

B) USING

C) AS

D) RENAME

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9. How is sensitive data protected in a database?

A) By auditing and monitoring activities

B) All of the above

C) By limiting user access

D) By using encryption

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10. Which SQL command is used to create a user?

A) NEW USER

B) ADD USER

C) INSERT USER

D) CREATE USER

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11. Which command is used to remove duplicate rows in a query result?

A) UNIQUE

B) GROUP BY

C) DISTINCT

D) FILTER

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12. Which clause is used to combine rows with the same values?

A) GROUP BY

B) DISTINCT

C) UNION

D) ORDER BY

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13. What is the difference between symmetric and asymmetric encryption in databases?

A) Symmetric encrypts only text; asymmetric encrypts all data

B) Asymmetric is faster than symmetric

C) Symmetric uses one key; asymmetric uses two keys

D) There is no difference

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14. Which clause is used to filter rows in a SELECT query?

A) GROUP BY

B) WHERE

C) HAVING

D) FILTER

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15. What does the GROUP BY clause do?

A) Sorts rows

B) Deletes duplicate rows

C) Filters rows

D) Groups rows with the same values

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16. Which SQL command is used to retrieve data from a database?

A) DELETE

B) UPDATE

C) SELECT

D) INSERT

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17. What does 'principle of least privilege' mean in database security?

A) Removing unused tables and columns

B) Allowing all users full database access

C) Assigning minimum access necessary for users

D) Encrypting sensitive data

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18. What is a primary key?

A) A duplicate identifier for a table record

B) None of the above

C) A command to fetch records

D) A unique identifier for a table record

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19. What is a view in SQL?

A) None of the above

B) A virtual table based on a query

C) A physical table

D) A key linking tables

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20. What is the purpose of the ROW_NUMBER() function?

A) Assigns unique numbers to rows within a partition

B) Creates a unique index

C) Assigns ranks with gaps for duplicates

D) Calculates the total number of rows in a table

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21. What type of dependency does 3NF eliminate?

A) Circular dependency

B) Multivalued dependency

C) Transitive dependency

D) Partial dependency

22 / 30

22. Which SQL command removes a table from the database?

A) DROP

B) TRUNCATE

C) DELETE

D) REMOVE

23 / 30

23. What is a security patch in database systems?

A) A backup of the database

B) A tool to optimize queries

C) A new feature added to the database

D) A fix for identified vulnerabilities

24 / 30

24. What is the purpose of the UNION operator?

A) Deletes records

B) Joins tables

C) Filters duplicate rows

D) Combines results of two queries

25 / 30

25. Which SQL function can identify the current user?

A) SESSION_USER()

B) USER()

C) CURRENT_USER()

D) All of the above

26 / 30

26. Which command is used to lock a table in SQL?

A) BLOCK TABLE

B) FREEZE TABLE

C) SECURE TABLE

D) LOCK TABLE

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27. Which SQL command is used to grant permissions to a user?

A) ALLOW

B) ASSIGN

C) PERMIT

D) GRANT

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28. Which aggregate function calculates the sum of a column?

A) MAX()

B) AVG()

C) COUNT()

D) SUM()

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29. What does the term 'atomicity' refer to in normalization?

A) Data contains multivalued attributes

B) Each cell contains a single, indivisible value

C) Data is stored in one table

D) Data is stored in multiple columns

30 / 30

30. How can database performance be monitored?

A) Analyzing query execution plans

B) Using performance monitoring tools

C) All of the above

D) Tracking server resource usage

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