About Wrong Join

Wrong Join is a SQL tutor that teaches by asking. It places you with a short diagnostic, keeps a map of eight skills, and questions you until you can do each one unaided.

How it works

The conversation comes from GLM, a large language model made by Z.ai. It can be wrong, so it isn't left in charge of your record. A separate program counts evidence and sets your levels, and query exercises are marked by running your SQL and comparing the result with a correct one.

Your queries run in your own browser on a copy of a practice database for a fictional bike shop. Nothing you run touches a server.

Credit

The teaching method is adapted from the socratic-tutor skill published by Jane Street under the MIT license, © 2026 Jane Street Group, LLC. Jane Street has no connection with this site. In-browser SQL is provided by sql.js.