Post #2417

✅SQL Interview Questions with Answers 1️⃣ Write a query to find the second highest salary in the employee table. SELECT MAX(salary) FROM employee WHERE salary < (SELECT MAX(salary) FROM employee); 2️⃣ Get the top 3 products by revenue from sales table. SELECT product_id, SUM(revenue) AS total_revenue FROM sales GROUP BY product_id ORDER BY total_revenue DESC LIMIT 3; 3️⃣ Use JOIN to combine customer and order data. SELECT c.customer_name, o.order_id, o.order_date FROM customers c JOIN orders o ON c.customer_id = o.customer_id; (That's an INNER JOIN—use LEFT JOIN to include all customers, even without orders.) 4️⃣ Difference between WHERE and HAVING? ⦁ WHERE filters rows before aggregation (e.g., on individual records). ⦁ HAVING filters rows after aggregation (used with GROUP BY on aggregates). Example: SELECT department, COUNT(*) FROM employee GROUP BY department HAVING COUNT(*) > 5; 5️⃣ Explain INDEX and how it improves performance. An INDEX is a data structure that improves the speed of data retrieval. It works like a lookup table and reduces the need to scan every row in a table. Especially useful for large datasets and on columns used in WHERE, JOIN, or ORDER BY—think 10x faster queries, but it slows inserts/updates a bit. 💬Tap ❤️ for more!