About SQL Practice

Why this exists

Setting up a database or a compiler just to practise is friction most learners don't need. This site removes that step: open a page and the sample tables, the Python interpreter or the JavaScript runtime are already there. Write code, run it, see the result — that's the whole loop. The site began as a SQL playground with five related sample tables (Employees, Departments, Customers, Products, Orders); that part is unchanged and still the deepest.

How it works

Everything that runs, runs inside your browser tab. Queries are parsed and executed by SQLite, a real SQL database engine compiled to WebAssembly and served from this site along with the pages. Python runs on CPython compiled to WebAssembly (Pyodide), also served from here; JavaScript and TypeScript run in an isolated background thread with no access to the page or the network. There is no backend server and no database that stores your code. The site publishes only languages with a working browser runner. Refresh a page and the sample data resets to its original state.

What you can do here

• Work through 42 guided exercises across four guided paths, from beginner to advanced, with your answer checked by actually running it against the sample database
• Run SELECT, JOIN, GROUP BY, subqueries, INSERT, UPDATE and DELETE freely against realistic sample data in the Playground
• Paste messy, unformatted SQL into the Formatter and get clean, consistently indented code back
• Browse the SQL tutorials to learn or refresh core SQL concepts
• Follow a learning path in SQL, Python or JavaScript: short lessons in order, with runnable examples, common mistakes and a program to write; TypeScript has a runnable playground
• Solve coding exercises that are checked by running your program against test cases
• Prepare for interviews with questions whose answers explain why

There are no accounts. Exercise progress is kept in your own browser, which means it stays private but also stays on this device. Completing a path unlocks a printable Certificate of Completion — a record of the practice you finished here, not an accredited qualification.

How we keep this accurate

A tutorial that teaches something wrong is worse than no tutorial. So this site holds itself to a mechanical standard rather than a hopeful one:

• Every runnable SQL example is executed before it is published. Each code block in the tutorials is run against the same sample database you use, by an automated script. If it errors or returns something misleading, it does not ship.
• Every exercise solution is verified the same way. All 42 reference solutions run against a freshly rebuilt copy of the database, and a browser-automation suite solves every exercise end-to-end the way a visitor would.
• Every program in every other language is executed too. Each lesson example, exercise solution, interview snippet and challenge solution is run with the real compiler or interpreter for its language before publishing, and the output shown on the page is what it printed. Each page names the toolchain used.
• Structured data must match the page. Anything the site tells search engines in schema markup is checked, string by string, against what actually renders for you.
• Accessibility is tested, not assumed. Every page is checked with axe-core against WCAG 2.1 AA before changes go live.
• Where our engine differs from big databases, we say so. Dialect differences are flagged in the text, and examples that need PostgreSQL or MySQL are labelled instead of pretended away.

The full editorial standard, including what the checks cover and what we will never do, is on the How we verify page. None of this makes the site infallible — it makes it correctable. If you catch a mistake anyway, tell us and it gets fixed.

Support the site

SQL Practice is free to use, and there is nothing to buy. It carries no advertising and sets no cookies — the whole site is static files and a database that runs inside your own browser, which keeps the running costs small enough to absorb. Page views and load times are counted cookielessly by our own host, as the Privacy Policy describes. Advertising may be added later to cover hosting; if that happens, the Privacy Policy will be updated to say so before any ad code goes live.