SQL Practice Problems with Online Checking

99 hands-on SQL exercises, from SELECT and WHERE to window functions, CTEs and table design. Use them to learn SQL from scratch, get comfortable with JOINs and GROUP BY, or prepare for a data analyst, developer or QA interview.

Every problem comes with a real-world scenario, the table schema and a sample of the expected output. The easiest way to solve them is the online trainer SQL Arena: write a query in your browser, press Submit, and your answer is checked right away against hidden data. Nothing to install — every problem runs on PostgreSQL, and many also on MySQL and ClickHouse.

• Statement — a short work scenario: what to find and how to present it.
• Tables — columns, types, primary (🔑) and foreign (→) keys.
• Expected columns and sample output — the fields the checker expects and the first rows of a correct result.
• "Solve online" link — the problem in the trainer, with an editor, a sandbox with data and automatic checking.

There are no ready-made solutions here on purpose: a problem you peeked at teaches nothing. The trainer compares your query with the reference on data you cannot see and tells you what is off: extra rows, wrong columns, wrong order.

1. Over-the-Counter Medications — easy
2. Customers from Berlin — easy
3. Platinum-Tier Members — easy
4. Long-Haul Flights — easy
5. Berlin Clubs — easy
6. Premium Subscriptions — easy
7. 5-Star Hotels — easy
8. Rock Artists — easy
9. Spacious Rooms — easy
10. Festivals in 2024 — easy
11. Endangered Species — easy
12. Savanna Residents — easy
13. Product Showcase: Rename the Columns — easy
14. Products Under 1000 Rubles — easy
15. Delivered Orders — easy
16. Customer card: projection with aliases — easy
17. Products from two warehouses — easy
18. Catalog Without Archive — easy
19. Warehouse shelf: SKU, weight and price under readable names — easy
20. Drop Unrated Reviews, Replace Empty Comments — easy

21. Monthly Sales Pulse — easy
22. Listening Hours by Month — easy
23. Store delivery scorecard — easy
24. A Customer's First Digital Footprint — easy
25. Duplicate Parcel Registrations — easy
26. Purchase Frequency in an Audio App — easy
27. Which Customers Need a Win-Back Campaign? — easy
28. From KYC Submission to Approval — easy
29. Most Read Books Lookup — easy
30. Kotomarket monthly orders report — medium
31. Top 3 categories by revenue — medium
32. Average Salary of Employees by Departments for 2023 — medium
33. Book Sales Split by Genre — medium
34. Analysis of courier performance by delivered packages — medium
35. Client Buying Behavior Study — medium
36. Sales Split by Product Category — medium
37. Box Office Revenue by Popular Genres — medium
38. Most prolific authors with high ratings — medium

39. Second-level shelves — easy
40. One-to-one, one-to-many — easy
41. Row fan-out after a JOIN — easy
42. Comparable apartment pairs — easy
43. Employees Shown with Their Departments — easy
44. Popular vehicles with multiple bookings — easy
45. Package delivery tracking by shipment codes — easy
46. Top players with high average score — medium
47. Analyzing Airline Route Profitability — medium
48. High-Volume and Profitable Products — medium
49. Most Active Authors by Published Articles Count — medium
50. Overloaded Hospital Departments — medium
51. Top hotel rooms by average rating and revenue — medium
52. Top companies by average applicant review rating — medium
53. Profitable room categories for the quarter — medium
54. Doctors with the highest patient complexity — medium
55. Analysis of insurance policy losses by region — medium
56. Top farmers' yield by crops — medium

57. Find the most expensive item — easy
58. Pull orders from Russian customers only — easy
59. Find orders bigger than average — easy
60. Customers who already ordered something — easy
61. Products that nobody bought — easy
62. Show every customer's order count — easy
63. Cheapest pick in every category — easy
64. Parcel scans after the watermark — easy
65. Documentary watchers — easy

66. Top Bank Clients by Transaction Amount — hard
67. Quarterly Performance of Sales Managers — hard
68. Top Couriers by Deliveries with Urgency Priority — hard
69. Employee Earnings Breakdown — hard
70. Monthly Top Tracks in Playlists — hard
71. Most-Played Artists Across Playlists — hard
72. Student Performance Ranking by Department with Grade Dynamics — hard
73. Revenue Month-on-Month Growth — hard

74. Gaps between plays — easy
75. Session-start flag in an online store — easy
76. Neobank Operating Balance — easy
77. Each Product's Share of Total Revenue via SUM() OVER () — medium
78. Staff Salaries: How Far From the Average — medium
79. Student Rating by Average Grade with Group Position — medium
80. Crop Variety Yield Rankings by Plot — medium
81. Genre Champions Among Library Readers — hard
82. Payout Trends Across Insurance Policies — hard
83. Gym Member Payment Momentum — hard
84. Fleet Revenue Growth by Month — hard
85. Monthly Box Office Peaks by Film — hard
86. Rising Stars of the Travel Agency — hard
87. Repeat Visit Intervals by Doctor — hard

88. Discount on Action games — easy
89. Seed a batch of test orders — easy
90. Spring cleaning — drop everything unpinned — easy
91. Save your first journal entry — easy
92. Pin every January note for the new year — easy
93. Add a test user — easy

94. Drop the Departments Table — easy
95. Add Email Column — easy
96. Drop Salary Column — easy
97. Rename Column name — easy
98. Normalization: split a flat book catalog into authors + books (PK/FK) — medium
99. Kotomarket: split an order into 3NF — medium

This repository holds 99 problems from the free part of the trainer. SQL Arena has more than 1,400: interview questions, a SQL course from scratch, courses on analytics, ClickHouse and Kafka, duels and a leaderboard.

Русская версия → sql-zadachi

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