25 SQL Interview Questions With Real Answers

If you are preparing for a data analyst, business intelligence, or data engineering role, SQL will definitely come up.

But here is the truth:
Most candidates practice syntax.
Interviewers test thinking.

In this guide, I will walk you through 25 SQL interview questions with real answers from beginner to advanced level — so you can confidently explain both the logic and the query.

Basic SQL Interview Questions

1. What is the difference between WHERE and HAVING?

• WHERE filters rows before aggregation
• HAVING filters after GROUP BY

SELECT department, COUNT(*)
FROM employees
GROUP BY department
HAVING COUNT(*) > 5;

2. What is the difference between INNER JOIN and LEFT JOIN?

• INNER JOIN returns matching records from both tables
• LEFT JOIN returns all records from the left table and matched records from the right table

3. How do you remove duplicates?

SELECT DISTINCT column_name
FROM table_name;

4. What does GROUP BY do?

It groups rows with the same values so aggregate functions (SUM, COUNT, AVG) can be applied.

5. How do you sort results?

SELECT *
FROM employees
ORDER BY salary DESC;

Intermediate SQL Interview Questions

6. How do you find the second highest salary?

SELECT MAX(salary)
FROM employees
WHERE salary < (SELECT MAX(salary) FROM employees);

7. How do you count NULL values?

SELECT COUNT(*) - COUNT(column_name)
FROM table_name;

8. What is a window function?

A function that performs calculations across a set of rows related to the current row.

Example:

SELECT employee_id,
       salary,
       RANK() OVER (ORDER BY salary DESC) AS salary_rank
FROM employees;

9. Difference between RANK() and DENSE_RANK()?

• RANK() skips numbers after ties
• DENSE_RANK() does not skip numbers

10. How do you use CASE statements?

SELECT employee_name,
       CASE
           WHEN salary > 100000 THEN 'High'
           ELSE 'Standard'
       END AS salary_category
FROM employees;

Advanced SQL Interview Questions

11. How do you identify duplicate records?

SELECT column_name, COUNT(*)
FROM table_name
GROUP BY column_name
HAVING COUNT(*) > 1;

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

• UNION removes duplicates
• UNION ALL keeps duplicates and is faster

13. How do you calculate running totals?

SELECT order_date,
       SUM(sales) OVER (ORDER BY order_date) AS running_total
FROM orders;

14. How do you find missing values between dates?

Use a calendar table and LEFT JOIN to detect gaps.

15. What is an index?

An index improves query performance by speeding up data retrieval.

Scenario-Based SQL Interview Questions

16. Find customers who never placed orders

SELECT c.customer_id
FROM customers c
LEFT JOIN orders o
ON c.customer_id = o.customer_id
WHERE o.customer_id IS NULL;

17. Calculate month-over-month growth

SELECT month,
       revenue,
       revenue - LAG(revenue) OVER (ORDER BY month) AS mom_growth
FROM sales;

18. Find top 3 products by sales

SELECT product_name
FROM (
    SELECT product_name,
           RANK() OVER (ORDER BY SUM(sales) DESC) AS rnk
    FROM sales
    GROUP BY product_name
) ranked
WHERE rnk <= 3;

19. How do you optimize slow queries?

• Add indexes
• Avoid SELECT *
• Filter early
• Use proper joins
• Analyze execution plans

20. What is normalization?

A database design technique to reduce redundancy and improve data integrity.

Practical Data Analyst SQL Questions

21. How do you pivot data?

Use CASE statements or built-in PIVOT functions (depending on database).

22. How do you handle NULL values?

SELECT COALESCE(column_name, 0)
FROM table_name;

23. Difference between DELETE, TRUNCATE, and DROP?

• DELETE removes rows
• TRUNCATE removes all rows quickly
• DROP removes the entire table

24. What is a CTE?

A Common Table Expression improves query readability.

WITH revenue_cte AS (
    SELECT customer_id, SUM(amount) AS total_spent
    FROM orders
    GROUP BY customer_id
)
SELECT *
FROM revenue_cte
WHERE total_spent > 1000;

25. What is the difference between a subquery and a join?

• A subquery is a query inside another query
• A join combines rows from multiple tables

If you average around 250 impressions per day on codewithfimi.com and want more clicks, SQL interview content is a strong traffic driver. It targets:

• Job seekers
• Bootcamp students
• Career switchers
• Junior analysts

To stand out, do not just memorize answers. Practice explaining:

• Why the query works
• When to use it
• Performance trade-offs

That is what separates average candidates from strong analysts.

FAQs