SQL and Databases coding problems

SQL questions are in almost every data, backend and analyst interview. Practise SELECT and filters, GROUP BY and HAVING, every kind of JOIN, subqueries and CTEs, then window functions, running totals and gaps and islands, checked on real PostgreSQL with hidden datasets.

64 problems: 28 easy, 25 medium, 11 hard. Free to read; a free account solves them and earns XP and Aura.

1. Average Order Value per CustomerPractice · SQL · +10 XP · group by, sql, aggregationeasy
2. Find Active InternsPractice · SQL · +10 XP · select and filter, sql, internshipeasy
3. Find Customers Who Placed Orders Above a Certain AmountPractice · SQL · +10 XP · select and filter, sql, aggregateeasy
4. Find Employees Working on ProjectsPractice · SQL · +10 XP · inner join, sql, employeeseasy
5. Find High-Scoring Students in PythonPractice · SQL · +10 XP · select and filter, sql, studentseasy
6. Find Products Below a Certain PricePractice · SQL · +10 XP · select and filter, sql, basic queryeasy
7. Find Students from a Specific CollegePractice · SQL · +10 XP · select and filter, sql, filteringeasy
8. Find Students with Missing Contact InfoPractice · SQL · +10 XP · null handling, sql, filteringeasy
9. Find Students with Missing EmailPractice · SQL · +10 XP · null handling, sql, filteringeasy
10. Find Students with Missing Email AddressesPractice · SQL · +10 XP · null handling, sql, filteringeasy
11. Find Students with Scores Above 80Practice · SQL · +10 XP · select and filter, sql, where clause1 solvedeasy
12. Find Unique Course EnrollmentsPractice · SQL · +10 XP · distinct values, sql, enrollmentseasy
13. Format College NamesPractice · SQL · +10 XP · string functions, sql, formattingeasy
14. Format Customer NamesPractice · SQL · +10 XP · string functions, sql, formattingeasy
15. Format Player NamesPractice · SQL · +10 XP · string functions, sql, formattingeasy
16. List Employees with No DepartmentPractice · SQL · +10 XP · null handling, sql, employeeseasy
17. List Unique Customer CitiesPractice · SQL · +10 XP · distinct values, sql, customerseasy
18. List Unique Product CategoriesPractice · SQL · +10 XP · distinct values, sql, productseasy
19. List Unique Student MajorsPractice · SQL · +10 XP · distinct values, sql, universityeasy
20. Number of Students per CollegePractice · SQL · +10 XP · group by, sql, countingeasy
21. Student Performance CategoriesPractice · SQL · +10 XP · case expressions, sql, studentseasy
22. Top 5 Highest Paid InternsPractice · SQL · +10 XP · sorting and limits, sql, rankingeasy
23. Top 5 Most Expensive GadgetsPractice · SQL · +10 XP · sorting and limits, sql, gadgetseasy
24. Total Items Sold by ProductPractice · SQL · +10 XP · aggregates, sql, group byeasy
25. Total Orders per CustomerPractice · SQL · +10 XP · aggregates, sql, group byeasy
26. Total Salary Expenditure by DepartmentPractice · SQL · +10 XP · aggregates, sql, group byeasy
27. Total Sales per Product CategoryPractice · SQL · +10 XP · aggregates, sql, group byeasy
28. Unique Course EnrollmentsPractice · SQL · +10 XP · distinct values, sql, enrollmenteasy
29. Active Interns in the Last 30 DaysPractice · SQL · +20 XP · date functions, sql, internshipsmedium
30. Average Score per Student GroupPractice · SQL · +20 XP · common table expressions, sql, aggregationmedium
31. CTE: Top Employee Performance RankingPractice · SQL · +20 XP · common table expressions, sql, rankingmedium
32. Customers with No OrdersPractice · SQL · +20 XP · anti join, sql, left joinmedium
33. Delivery Performance RankingPractice · SQL · +20 XP · window functions, sql, rankingmedium
34. Dishes Present in Only One Cuisine TypePractice · SQL · +20 XP · set operations, sql, subquerymedium
35. Find Departments with Above Average Salary SpendingPractice · SQL · +20 XP · subqueries, sql, aggregationmedium
36. Find Employee's Manager NamePractice · SQL · +20 XP · self join, sql, hierarchymedium
37. Find Employees With No Direct ReportsPractice · SQL · +20 XP · self join, sql, hierarchymedium
38. Find Interns with Above Average SalaryPractice · SQL · +20 XP · subqueries, sql, aggregationmedium
39. Find Students with Above-Average GPA in Their DepartmentPractice · SQL · +20 XP · subqueries, sql, aggregationmedium
40. Intern Stipend by Department and Start DatePractice · SQL · +20 XP · multi-table joins, sql, aggregationmedium
41. Internship Offers by Company and DepartmentPractice · SQL · +20 XP · multi-table joins, sql, aggregationmedium
42. Internship Offers by Department and SalaryPractice · SQL · +20 XP · multi-table joins, sql, aggregationmedium
43. Internship Offers by Status and DepartmentPractice · SQL · +20 XP · conditional aggregation, sql, internshipsmedium
44. Internship Performance by DepartmentPractice · SQL · +20 XP · multi-table joins, sql, aggregationmedium
45. Order Delivery Time CalculationPractice · SQL · +20 XP · date functions, sql, deliverymedium
46. Rank Sales by Consecutive DaysPractice · SQL · +20 XP · window functions, sql, rankingmedium
47. Rank Student Scores in Each SubjectPractice · SQL · +20 XP · window functions, sql, rankingmedium
48. Rank Students by Cumulative Score in Each CollegePractice · SQL · +20 XP · window functions, sql, rankingmedium
49. Student Course Ranking by SemesterPractice · SQL · +20 XP · window functions, sql, rankingmedium
50. Students with Above Average GPA in Their DepartmentPractice · SQL · +20 XP · subqueries, sql, aggregationmedium
51. Top 2 Interns by Monthly Stipend in Each DepartmentPractice · SQL · +20 XP · top n per group, sql, window functionsmedium
52. Top 3 Interns by Monthly Stipend in Each DepartmentPractice · SQL · +20 XP · top n per group, sql, window functionsmedium
53. Top 3 Most Frequent Items per CustomerPractice · SQL · +20 XP · top n per group, sql, window functionsmedium
54. Consecutive Delivery DelaysPractice · SQL · +30 XP · lag and lead, sql, window functionshard
55. Cricket Performance: Consecutive Matches Above AveragePractice · SQL · +30 XP · window functions, sql, streakshard
56. Cumulative Sales Over Time with LagPractice · SQL · +30 XP · running totals, sql, window functionshard
57. E-commerce Sessionization: Time Between PurchasesPractice · SQL · +30 XP · sessionization, sql, analyticshard
58. Find All Ancestors of a ProductPractice · SQL · +30 XP · recursive cte, sql, hierarchyhard
59. Median Customer Order Value by RegionPractice · SQL · +30 XP · percentiles and medians, sql, window functionshard
60. Median Order Value Per Customer GroupPractice · SQL · +30 XP · percentiles and medians, sql, window functionshard
61. Organizational Hierarchy with TenurePractice · SQL · +30 XP · recursive cte, sql, hierarchyhard
62. Running Total of Delivery Charges per CityPractice · SQL · +30 XP · running totals, sql, window functionshard
63. Sales Performance: Rank by Consecutive UpswingPractice · SQL · +30 XP · window functions, sql, rankinghard
64. Top Salaries per DepartmentPractice · SQL · +30 XP · window functions, ranking, sqlhard