Wipro · SQL & Databases

Wipro SQL & Databases interview questions

Practice SQL & Databases questions specifically asked in Wipro interviews – ideal for online test preparation, technical rounds and final HR discussions.

Company: WiproSubject: SQL & Databases80 questions in this page

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Wipro · SQL & Databases questions (80)

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1. Which option best describes a correlated subquery?

Difficulty: EasyType: MCQTopic: Subqueries & CTEs

A correlated subquery depends on the current row of the outer query. The database must re-evaluate it for each outer row. This design is expressive, but can be slow if the inner expression is not selective or not indexed. Many engines can transform it into a join when the logic allows.

Example code

SELECT e.emp_id
FROM employees e
WHERE e.salary > (
  SELECT AVG(salary)
  FROM employees x
  WHERE x.dept_id = e.dept_id
);

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Wipro SQL & Databases interview questions

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1. Which option best describes a correlated subquery?

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

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

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

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

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

7. How can you help the optimizer avoid an explicit SORT operator for ORDER BY?

8. Describe a strategy to stabilize performance for a parameterized search endpoint suffering from plan cache instability.

9. Which predicate most closely mirrors a semi-join?

10. Explain how to compute a 7-day moving average per product. Mention the window frame choice and why.

11. Which trade-off best describes surrogate keys (e.g., identity/UUID) compared to natural keys?

12. Explain index maintenance: fragmentation, page splits, fillfactor, and when to rebuild versus reorganize.

13. When does a temporary table often outperform a large CTE?

14. Your plan shows sort or hash spills to disk. What are the likely causes and remedies?

15. Which pairing of read phenomenon and description is correct?

16. Explain write skew under snapshot isolation and how to prevent it.

17. Which principle should guide database permission design for application users?

18. Why must you test restores and not only take backups? Outline a simple validation routine.

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

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

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

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

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

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

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

26. What does an INNER JOIN return?

27. What does a FULL OUTER JOIN return?

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

29. Which set operator keeps duplicates?

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

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

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

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

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

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

36. What is a covering index?

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

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

39. Which LIKE predicate can use a standard B-tree index in most engines?

40. Why is keyset pagination often better than OFFSET/LIMIT on large result sets? Show the pattern.

41. Your search uses LOWER(email) = 'x@y.com'. How do you keep it SARGable without changing callers?

42. Which join algorithm is typically best when both inputs are already sorted on the join key?

43. When can rewriting a wide OR predicate as UNION ALL improve performance?

44. Which constraint ensures column values satisfy a Boolean expression?

45. When would you prefer a temporary table over a CTE for performance?

46. Which option correctly expands the A C I D properties for relational transactions?

47. Which pairing of lock type and operation is most accurate for row-level locking?

48. What risk comes with using a WITH (NOLOCK) or READ UNCOMMITTED hint in a reporting query?

49. Contrast Snapshot Isolation with true Serializable isolation. When does Snapshot still allow anomalies?

50. Why are long-running transactions harmful in MVCC systems, and how do you mitigate the damage?

51. Which statement best distinguishes a correlated subquery from a non-correlated subquery?

52. Why can UNION ALL be faster than UNION?

53. What is a practical use of a SELF JOIN?

54. How do you prevent infinite loops and duplicates in a recursive CTE that walks a graph?

55. Which window function assigns a unique sequence number to each row within its partition even when values tie?

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

57. Which frame reliably produces a cumulative running total from the first row to the current row?

58. Portable way to count only paid orders in a window when FILTER clause is unavailable?

59. When would you use PERCENT_RANK or CUME_DIST instead of DENSE_RANK for analytics?

60. Which statement correctly contrasts a PRIMARY KEY with a UNIQUE constraint?

61. Compare using constraints versus triggers to enforce business rules. When is each appropriate?

62. Explain how normalization up to 3NF helps prevent insert, update, and delete anomalies. Give a short example.

63. For general-purpose predicates (=, <, <=, BETWEEN, ORDER BY), which index type is usually the default and most versatile?

64. Which statement best describes a clustered index in systems that support it (e.g., SQL Server)?

65. On which type of column does an index typically give the biggest benefit?

66. Why can too many indexes slow down an OLTP workload?

67. Explain SARGability and give two examples of non-SARGable predicates with index-friendly rewrites.

68. What does EXPLAIN (or EXPLAIN ANALYZE) primarily show you?

69. What is parameter sniffing and how can it hurt performance?

70. You see large gaps between estimated and actual rows in a plan. Walk through a systematic way to fix this.

71. Which option correctly lists the ACID properties for transactions?

72. What is a practical strategy to reduce deadlocks in a high-contention workload?

73. How would you design safe retries for transient errors like deadlocks or lock timeouts?

74. What does Row-Level Security (RLS) enforce?

75. Why expose a VIEW to consumers instead of the base table?

76. Which combination enables point-in-time recovery (PITR)?

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