✅ Top 50 SQL Interview Questions

1. What is SQL and why is it used?
2. Difference between SQL and MySQL
3. What are primary keys and foreign keys?
4. What is a unique constraint?
5. Difference between WHERE and HAVING
6. What are joins? Types of joins?
7. Difference between INNER JOIN and LEFT JOIN
8. What is a subquery?
9. What are CTEs (Common Table Expressions)?
10. What is a view in SQL?
11. How do you remove duplicate records?
12. What is normalization? Explain its types
13. What is denormalization?
14. What is a stored procedure?
15. What are indexes and why are they used?
16. What is the difference between clustered and non-clustered index?
17. What is a transaction?
18. ACID properties in SQL
19. Difference between DELETE, TRUNCATE, and DROP
20. What is a NULL value in SQL?
21. How do you handle NULLs in queries?
22. What is COALESCE() in SQL?
23. What are aggregate functions?
24. What is GROUP BY and how does it work?
25. What is the difference between COUNT(*) and COUNT(column)?
26. What are window functions?
27. Difference between RANK(), DENSE_RANK(), and ROW_NUMBER()
28. What is the use of LAG() and LEAD()?
29. What is a CASE statement?
30. What is the difference between CHAR and VARCHAR?
31. What are constraints in SQL?
32. What is a composite key?
33. What are scalar vs table-valued functions?
34. How does indexing affect performance?
35. What is data integrity?
36. What are triggers in SQL?
37. What is a correlated subquery?
38. What is a cross join?
39. What is UNION vs UNION ALL?
40. Difference between EXISTS and IN
41. What are set operations in SQL?
42. What is a materialized view?
43. Explain the BETWEEN operator
44. What is a pivot table in SQL?
45. How do you optimize SQL queries?
46. How do you handle slow queries?
47. What is execution plan in SQL?
48. What’s the use of LIMIT / OFFSET?
49. How do you import/export data in SQL?
50. How would you clean messy data using SQL?

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