Admin

03-22-2026, 06:39 AM #1

SQL is tested in almost every company interview. Must-know queries:

1. Find the second highest salary
2. Find duplicate records in a table
3. Difference between WHERE and HAVING
4. INNER JOIN vs LEFT JOIN vs RIGHT JOIN
5. Write a query using GROUP BY and ORDER BY
6. Subqueries vs JOINs - when to use which
7. Find employees who earn more than their manager
8. Nth highest salary using DENSE_RANK()
9. Delete duplicate rows keeping one
10. Self JOIN examples
11. UNION vs UNION ALL
12. Indexes and their impact on performance
13. Normalization forms (1NF, 2NF, 3NF, BCNF)
14. Triggers and Stored Procedures basics
15. ACID properties explanation

Practice on HackerRank SQL challenges and LeetCode Database problems.

indian

03-22-2026, 06:50 AM #2

SQL is tested in almost every company interview and these 15 queries cover the most commonly asked ones. Practicing on HackerRank and LeetCode is great advice for building confidence!

mohan

03-22-2026, 07:10 AM #3

These SQL queries are asked in nearly every placement interview. Finding the second highest salary is a classic question with multiple approaches using subqueries or DENSE_RANK. I'd recommend practicing writing queries by hand without an IDE, as some interviews require whiteboard SQL. Understanding the difference between WHERE and HAVING, and when to use subqueries vs JOINs is essential. Self JOINs are tricky but come up often. Practice on platforms like SQLZoo or W3Schools SQL exercises.