SQL · ERDs · Normalization
A new SQL challenge every day on realistic business data, ERD drills in Crow's Foot notation, and normalization step by step. Every answer is checked instantly, with feedback that tells you what to fix.
Free while in pilot. Runs in your browser, nothing to install.
SELECT country, COUNT(*) AS customers FROM customers GROUP BY country ORDER BY customers DESC, country;
| country | customers |
|---|---|
| United States | 12 |
| United Kingdom | 9 |
| Portugal | 8 |
| Canada | 7 |
| Kenya | 6 |
Showing 5 of 7 rows.
01 · Daily challenge
Twelve challenges from SELECT to window functions on a sample computer store. The checker spots the difference: wrong row count, right rows in the wrong order, columns swapped. Keep your streak going with a new challenge each day.
Browse the challenges →02 · ERD Lab
Read the Crow's Foot symbols, drill one skill at a time, then draw a full diagram. Feedback covers each entity, every cardinality and where the keys belong.
03 · Normalization
Watch real tables move from unnormalized form to Third Normal Form, with the problem columns highlighted at each step. Then open the finished schema and query it.
Read the worked example →For lecturers
Students practise the topics they struggle with most, at their own pace, with feedback you'd otherwise give by hand. A class dashboard for assigning work and tracking progress is in development with pilot lecturers.