Practice SQL with a real database, right in the browser.
Every query you write runs against SQLite compiled to WebAssembly — on your machine, not a server. 36 questions, from first SELECTs to window functions, with instant pass/fail feedback.
The loop
Open a question. Write SQL. Get graded.
No sign-up, no backend, no waiting. Your answer is checked against hidden fixtures with edge cases — duplicates, NULLs, and ties — so passing actually means something.
- 01
Read the prompt and schema
The left panel shows the question, the schema explorer, and sample rows you can click through.
- 02
Write and run SQL in a full editor
Monaco with syntax highlighting and Ctrl/⌘+Enter to run. Results render instantly from the local engine.
- 03
Submit for pass/fail validation
Your query runs against every hidden fixture. Pass all of them and the question is marked complete — in this browser.
Your data never leaves your device
SQL runs in a Web Worker via SQLite WASM. Drafts, progress, bookmarks, and notes live only in this browser's IndexedDB. There is no backend, no analytics, no authentication.
The catalogue
36 questions, 16 to start easy.
Ordered from easy to hard so the curve stays gentle. Filter by difficulty, topic, or a keyword to focus a session.
View the full catalogue- 01easy
Active Users Per Day
Report the number of distinct active users for each date of activity.
- 02easy
Article Views I
Find the authors who viewed their own articles at least once.
- 03easy
Average Process Time Per Machine
Compute each machine's average time to complete a process.
- 04easy
Big Countries
Find countries with a large area or population.
- 05easy
Classes With At Least 5 Students
Find classes with five or more students enrolled.
- 06easy
Customers Without Orders
List customers who have never placed an order using an anti-join.
- 07easy
Duplicate Emails
List the email addresses that appear more than once in the person table.
- 08easy
Employee Bonus
Report every employee's name and bonus, including those with none.
- 09easy
Employees Earning More Than Their Manager
Find employees whose salary is greater than their direct manager's salary.
- 10easy
Find Customer Referee
Find customers who are not referred by customer id 2.
24 topics covered — from basic SELECTs to window functions and NULL handling.