✅ Introduction
SQL (Structured Query Language) is the foundation of most modern database systems. Whether you’re preparing for a backend developer role or a data analyst interview, mastering SQL questions for interview is key to cracking technical rounds.
In this article, we’ll walk you through 25 essential SQL interview questions, real-life SQL query interview questions and answers, and practical examples. This guide strictly follows Google’s E-E-A-T (Experience, Expertise, Authoritativeness, Trustworthiness) principles and has been reviewed by data experts at CapableTechies.
📌 Why SQL Skills Matter in 2025
💼 80%+ tech jobs require SQL skills
⚙️ Used in data analytics, backend development, automation, and reporting
🔒 Still the #1 choice for enterprise databases (PostgreSQL, MySQL, Oracle, SQL Server)
💡 Top 25 SQL Questions for Interview with Answers
1. What is SQL?
- SQL is a language for querying and managing data in relational databases. It helps users perform operations like SELECT, INSERT, UPDATE, DELETE, and more.
2. What is the difference between DDL, DML, and DCL?
| Type | Purpose | Examples |
|---|---|---|
| DDL | Defines DB structure | CREATE, ALTER, DROP |
| DML | Manipulates data | INSERT, UPDATE, DELETE |
| DCL | Controls access | GRANT, REVOKE |
3. What is a Primary Key vs Foreign Key?
Primary Key: Uniquely identifies records in a table.
Foreign Key: Refers to the primary key of another table.
4. What is the difference between WHERE and HAVING?
WHERE: Filters rows before aggregation.
HAVING: Filters groups after aggregation.
SELECT department, COUNT(*) FROM employees
GROUP BY department HAVING COUNT(*) > 10;
5. What are different types of JOINs in SQL?
INNER JOIN
LEFT JOIN
RIGHT JOIN
FULL OUTER JOIN
SELF JOIN
SELECT e.name, d.dept_name
FROM employees e
INNER JOIN departments d ON e.dept_id = d.id;
6. What is normalization?
Normalization organizes data to reduce redundancy.
1NF: No repeating groups
2NF: No partial dependency
3NF: No transitive dependency
7. What is a subquery?
A subquery is a query nested inside another query.
SELECT name FROM employees
WHERE dept_id = (SELECT id FROM departments WHERE name = 'HR');
8. Difference between DELETE, TRUNCATE, and DROP?
| Operation | Description | Rollback |
|---|---|---|
| DELETE | Removes specific rows | Yes |
| TRUNCATE | Removes all rows | No |
| DROP | Deletes entire table | No |
9. What are indexes in SQL?
Indexes improve SELECT query performance by providing quick access to rows.
CREATE INDEX idx_emp_name ON employees(name);
10. What is the use of GROUP BY in SQL?
GROUP BY groups records based on one or more columns and is often used with aggregate functions like COUNT, SUM, AVG.
🧪 10 Practical SQL Query Interview Examples
Find the second highest salary:
SELECT MAX(salary) FROM employees
WHERE salary < (SELECT MAX(salary) FROM employees);
List employees with the same department:
SELECT name FROM employees
WHERE dept_id IN (SELECT dept_id FROM employees GROUP BY dept_id HAVING COUNT(*) > 1);
Retrieve duplicate records:
SELECT name, COUNT(*)
FROM employees
GROUP BY name HAVING COUNT(*) > 1;
Get the highest-paid employee:
SELECT * FROM employees
ORDER BY salary DESC LIMIT 1;
Join three tables:
SELECT e.name, d.dept_name, l.location
FROM employees e
JOIN departments d ON e.dept_id = d.id
JOIN locations l ON d.loc_id = l.id;
Fetch 5 highest salaries:
SELECT DISTINCT salary FROM employees
ORDER BY salary DESC LIMIT 5;
Update salaries:
UPDATE employees SET salary = salary * 1.1 WHERE performance = 'A+';
Delete all interns:
DELETE FROM employees WHERE designation = 'Intern';
Find employees hired in the last 6 months:
SELECT * FROM employees
WHERE hire_date >= DATE_SUB(CURDATE(), INTERVAL 6 MONTH);
Count employees by role:
SELECT designation, COUNT(*) FROM employees
GROUP BY designation;
❓ Detailed FAQs on SQL Interview Questions
Q1. How can I prepare for SQL interview questions effectively?
Practice real SQL queries using platforms like LeetCode or HackerRank.
Understand SQL JOINs, aggregate functions, subqueries, and data types deeply.
Use guides like this on Fresh Blog or CapableTechies.com.
Q2. Are SQL interviews only theoretical?
No. Many companies include hands-on query rounds where you must write or debug SQL code live or using a shared editor.
Q3. What databases should I be familiar with?
Focus on MySQL, PostgreSQL, SQL Server, and SQLite. Oracle SQL can also be useful for enterprise roles.
Q4. Should I memorize all commands?
No need to memorize — but understanding syntax, logic, and application is critical. Use tools like DB Fiddle for practicing.
Q5. What soft skills are important alongside SQL knowledge?
Explaining your logic clearly
Clean formatting
Collaboration with data teams
Handling performance discussions (e.g., when to use indexes)
Conclusion: Ace Your SQL Interview with Confidence
Preparing for SQL interviews doesn’t have to be overwhelming. With these top 25 SQL questions for interview, clear answers, and real-world query examples, you now have a solid foundation to face any technical round with confidence.
From mastering basic commands to tackling complex joins and subqueries, your SQL knowledge will set you apart in 2025’s data-driven job market. Keep practicing, stay curious, and remember — every great developer once started with their first query.
👉 Read more expert guides and technical blogs on Capable Techies to stay ahead in your learning journey.
