SQL & Databases · Complete Question Bank

All SQL & Databases Interview Questions

Practice the complete collection of SQL & Databases interview questions including theory, coding, MCQs and real interview problems.

Total Questions: 216Topics: 11Complete interview preparation

Overview

Questions

216

Full database

Topics

Categorised

Difficulty

Mixed Levels

Easy Hard

All SQL & Databases Interview Questions (216)

Scroll through every important SQL & Databases question asked in real interviews. Includes MCQs, subjective questions, and coding prompts.

1. Which SQL statement retrieves all columns and rows from a table named employees?

Difficulty: EasyType: MCQTopic: SQL Basics & DML

READ * FROM employees;
SELECT ALL FROM employees;
SELECT * FROM employees;
GET * FROM employees;

SELECT chooses columns and rows from one or more tables. The star is a shorthand for all columns. In production, prefer listing columns to control payloads, avoid hidden schema breaks, and help indexes get used effectively.

Correct Answer: SELECT * FROM employees;

Example Code

SELECT * FROM employees;

2. Which clause filters rows before aggregation and affects which rows are grouped?

Difficulty: EasyType: MCQTopic: SQL Basics & DML

Continue your preparation

Browse more SQL & Databases questions, explore related subjects, or practice full interview sets to strengthen your preparation.

SQL & Databases subject page•All subjects

Master Interviews Anywhere, Anytime

All SQL & Databases Interview Questions

Overview

1. Which SQL statement retrieves all columns and rows from a table named employees?

2. Which clause filters rows before aggregation and affects which rows are grouped?

Continue your preparation

3. What is the default sort order when ORDER BY is used without ASC or DESC?

4. Which construct is commonly used to paginate results in SQL engines like Postgres and MySQL?

5. Which predicate correctly checks for missing values in standard SQL?

6. What is the main purpose of using column or table aliases in a SELECT statement?

7. Which query returns rows where city is either 'Delhi' or 'Mumbai'?

8. Which statement inserts a single row into a table?

9. What is the safest pattern to update or delete rows in production?

10. Why do many teams avoid SELECT * in production queries? Give practical reasons.

11. Explain how NULL affects comparisons, sorting, and aggregates. How do you handle it safely?

12. Describe how LIKE works with % and _ wildcards. When should you avoid it?

13. How do you choose appropriate data types for columns, and why does it matter?

14. Outline a safe pattern to perform a multi-step change: insert a row, update a counter, and read back the result.

15. You need customers who placed more than 5 orders in 2025. Where should the date filter go and where should the count filter go?

16. Which statement about COUNT is correct?

17. In standard SQL, which SELECT list is valid with GROUP BY?

18. How do you count unique paying customers per month?

19. What is a common pattern to compute conditional totals in a single pass?

20. Which is the best practice when filtering rows on a simple column value for a grouped report?

21. You need average rating per product, but some rows have NULL rating. What does AVG(rating) return?

22. What’s a portable way to group daily sales by date if your engine lacks DATE_TRUNC?

23. In PostgreSQL, which syntax cleanly aggregates only rows that match a condition without CASE?

24. After aggregating, which is the simplest way to sort by the computed total?

25. Explain how CASE and COALESCE help build robust grouped reports when data is messy.

26. How would you return each customer’s latest order total without losing other customers? Compare two approaches.

27. You need products with zero sales in 2025. Show two correct patterns and explain their trade-offs.

28. How do DISTINCT and GROUP BY differ when removing duplicates, and when would you prefer one?

29. Describe a query to return the top 3 products by revenue in each category and explain tie handling.

30. What does an INNER JOIN return?

31. Which statement about LEFT JOIN is correct?

32. How does a RIGHT JOIN relate to a LEFT JOIN?

33. What does a FULL OUTER JOIN return?

34. What is a CROSS JOIN?

35. When do you use a SELF JOIN?

36. Which pattern correctly returns rows in A that have no match in B?

37. How do you select rows from A that have at least one match in B without duplicating A due to multiple matches?

38. In a LEFT JOIN, where should you place a filter on the right table's column to avoid unintentionally turning it into an INNER JOIN?

39. Which set operator keeps duplicates?

40. After joining orders to order_items, your totals are doubled. Why did this happen, and how do you fix it?

41. Compare NOT EXISTS with NOT IN for anti-joins. When can NOT IN produce surprising results?

42. Your engine lacks FULL OUTER JOIN. How can you emulate it, and what are the trade-offs?

43. How does join order and indexing affect performance in multi-table joins?

44. Explain when to put predicates in ON versus WHERE for outer joins. Give a rule of thumb.

45. Which option best describes a correlated subquery?

46. You must return customers who have at least one order. Which pattern is most robust and avoids duplicate inflation?

47. When can NOT IN return zero rows unexpectedly?

48. What is a main benefit of using a Common Table Expression (CTE) with WITH?

49. Which statement about using multiple CTEs is correct?

50. In a recursive CTE, what are the two essential parts?

51. Which pattern safely updates a table based on a value computed by a subquery?

52. Which is often faster for existence checks on large, indexed tables?

53. Which statement compares a CTE and a temporary table accurately?

54. Explain how you would use a CTE to deduplicate users by email while keeping the most recent row.

55. How do you traverse a hierarchy with a recursive CTE to get full paths and depths? How do you avoid cycles?

56. Show how you would express an anti-join using NOT EXISTS and explain why it handles NULLs correctly.

57. Compare a correlated subquery and a window function to get each department’s highest paid employee.

58. Do CTEs always improve performance? Explain how engines may inline or materialize them and how you decide.

59. Which statement correctly contrasts ROW_NUMBER(), RANK(), and DENSE_RANK()?

60. In a window definition, what do PARTITION BY and ORDER BY control?

61. Which frame returns a classic running total that includes the current row?

62. How do you compute a 7-day moving average per product using window functions?

63. What does LAG(value, 1, 0) return when there is no previous row in the partition?

64. FIRST_VALUE and LAST_VALUE often need an explicit frame. Why?

65. Which pair are window ranking distribution functions useful for relative standing?

66. How do GROUP BY aggregations differ from window aggregations?

67. You want a running total that resets each month per customer. What is the correct setup?

68. How would you compute a running total that only counts 'PAID' invoices while still showing all invoice rows?

69. Explain how to compute day-over-day change and growth rate for a metric using window functions.

70. Describe two ways to return the top 3 products by revenue in each category and discuss tie handling.

71. What pitfalls arise from using RANGE frames with duplicate ORDER BY values, and how do you avoid them?

72. When would you prefer window functions over self-joins for comparative analytics, and why?

73. Some warehouses support QUALIFY to filter on window results. Without QUALIFY, how do you structure the query cleanly?

74. What is the defining property of a clustered index?

75. When does a non-clustered index help most?

76. Which column is the best candidate for an index from a selectivity perspective?

Master Interviews
Anywhere, Anytime