Top SQL Interview Questions and Answers for 2025 

Structured Query Language (SQL) is the backbone of relational database management systems. From small startups to global enterprises, SQL is used everywhere to manage, query, and manipulate data. Whether you’re applying for a role as a software developer, database administrator, or data analyst, you can expect SQL-related questions in your technical interviews.

This guide brings you the top SQL interview questions and answers for 2025. We’ll cover both basic and advanced topics, along with examples, so you can feel confident when walking into your next interview.

1. What is SQL?

Answer:
SQL (Structured Query Language) is a standard language used to interact with relational databases. It allows you to create, read, update, and delete (CRUD) data. SQL is used in popular databases like MySQL, PostgreSQL, Oracle, and SQL Server.

2. What is the difference between SQL and MySQL?

Answer:

• SQL: A standard language used to manage databases.
  
  

• MySQL: A database management system (DBMS) that uses SQL as its query language.
  
  

So, SQL is the language, and MySQL is the software.

3. What are the different types of SQL commands?

Answer:
SQL commands are grouped into categories:

• DDL (Data Definition Language): CREATE, ALTER, DROP, TRUNCATE
  
  

• DML (Data Manipulation Language): SELECT, INSERT, UPDATE, DELETE
  
  

• DCL (Data Control Language): GRANT, REVOKE
  
  

• TCL (Transaction Control Language): COMMIT, ROLLBACK, SAVEPOINT
  
  

4. What is the difference between DELETE, TRUNCATE, and DROP?

Answer:

• DELETE: Removes rows from a table (can include WHERE clause).
  
  

• TRUNCATE: Removes all rows but keeps the table structure intact.
  
  

• DROP: Removes the entire table and its structure.
  
  

5. What are primary keys and foreign keys?

Answer:

• Primary Key: Uniquely identifies each record in a table. Cannot have NULL values.
  
  

• Foreign Key: A field in one table that refers to the primary key in another table, establishing a relationship between the two tables.
  
  

6. What is the difference between WHERE and HAVING?

Answer:

• WHERE: Filters rows before grouping.
  
  

• HAVING: Filters groups after aggregation.
  
  

Example:

SELECT department, COUNT(*)

FROM employees

WHERE salary > 50000

GROUP BY department

HAVING COUNT(*) > 5;

7. What are Joins in SQL?

Answer:
Joins combine rows from two or more tables based on related columns.

Types of joins:

• INNER JOIN: Returns rows with matching values in both tables.
  
  

• LEFT JOIN: Returns all rows from the left table and matching rows from the right.
  
  

• RIGHT JOIN: Returns all rows from the right table and matching rows from the left.
  
  

• FULL JOIN: Returns all rows when there’s a match in either table.
  
  

8. What is normalization?

Answer:
Normalization is the process of organizing data to reduce redundancy and improve data integrity.

Common forms:

• 1NF: Atomic values (no repeating groups).
  
  

• 2NF: Must be in 1NF + no partial dependency.
  
  

• 3NF: Must be in 2NF + no transitive dependency.
  
  

9. What are indexes in SQL?

Answer:
Indexes are database objects that improve the speed of data retrieval at the cost of additional storage and slower write operations.

Types:

• Clustered Index: Alters the way records are stored (one per table).
  
  

• Non-clustered Index: Creates a separate structure pointing to the data.
  
  

10. What is a subquery?

Answer:
A subquery is a query within another query.

Example:

SELECT name, salary

FROM employees

WHERE salary > (SELECT AVG(salary) FROM employees);

This finds employees with salaries higher than the average.

11. What is the difference between UNION and UNION ALL?

Answer:

• UNION: Combines result sets and removes duplicates.
  
  

• UNION ALL: Combines result sets but keeps duplicates.
  
  

12. What are stored procedures?

Answer:
A stored procedure is a precompiled collection of SQL statements stored in the database. It improves performance and promotes reusability.

Example:

CREATE PROCEDURE GetEmployees

AS

SELECT * FROM employees;

13. What are triggers in SQL?

Answer:
A trigger is a stored program that automatically executes when a specified event occurs in a database (like INSERT, UPDATE, DELETE).

14. What is a view in SQL?

Answer:
A view is a virtual table created using a SQL query. It doesn’t store data itself but displays results based on underlying tables.

Example:

CREATE VIEW HighSalary AS

SELECT name, salary FROM employees WHERE salary > 60000;

15. What is ACID in SQL?

Answer:
ACID ensures reliable transactions:

• Atomicity: All or nothing.
  
  

• Consistency: Maintains database rules.
  
  

• Isolation: Transactions don’t interfere with each other.
  
  

• Durability: Once committed, changes are permanent.
  
  

16. What is the difference between OLTP and OLAP?

Answer:

• OLTP (Online Transaction Processing): Handles real-time transactions (e.g., banking).
  
  

• OLAP (Online Analytical Processing): Handles complex queries for analysis (e.g., business reports).
  
  

17. What is the difference between RANK(), DENSE_RANK(), and ROW_NUMBER()?

Answer:

• ROW_NUMBER(): Unique sequential number for each row.
  
  

• RANK(): Assigns ranks but skips numbers for ties.
  
  

• DENSE_RANK(): Assigns ranks without gaps for ties.
  
  

18. How do you optimize SQL queries?

Answer:

• Use indexes wisely.
  
  

• Avoid SELECT *.
  
  

• Use joins instead of subqueries where possible.
  
  

• Analyze execution plans.
  
  

• Normalize tables to reduce redundancy.
  
  

19. What are CTEs (Common Table Expressions)?

Answer:
CTEs are temporary result sets that can be referenced within a query.

Example:

WITH DeptSalary AS (

  SELECT department, AVG(salary) AS avg_salary

  FROM employees

  GROUP BY department

)

SELECT * FROM DeptSalary WHERE avg_salary > 60000;

20. What trends should SQL professionals know in 2025?

Answer:

• Integration with cloud databases like AWS RDS, Azure SQL, Google BigQuery.
  
  

• SQL + AI/ML pipelines for advanced analytics.
  
  

• Serverless databases for scalability.
  
  

• NoSQL + SQL hybrid systems gaining traction.
  
  

• Automation tools for query optimization.
  
  

Final Thoughts

SQL remains the universal language of data, and mastering it opens doors to countless opportunities in tech. This guide of top SQL interview questions and answers for 2025 is designed to help you prepare for interviews by covering everything from fundamentals to advanced topics.

Whether you’re aiming for a junior developer role or a senior data engineering position, practicing these questions with real-world examples will boost your confidence.

Remember: the best way to learn SQL is through hands-on practice. Set up a sample database, experiment with queries, and test yourself. With preparation and persistence, you’ll ace your next interview.

So next time someone asks you about SQL Interview Questions, you’ll be ready with clear, practical, and confident answers.