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Choose where to start

New to SQL?

SQL foundations

Four free lessons on tables, columns, filters and sorting.

Start SQL foundations

Already write SQL?

SQL performance

54 exercises on indexes, joins and query plans. The first module is free.

Start the free module

SQL guides

What the performance course covers

Plan on about 9 to 22 hours.

Practice rewriting SQL while preserving duplicates, NULLs and ordering. Compare plans, test your answer on edge cases, and try another case of the same concept.

1Reading queriesFree10 exercises
2How queries run10 exercises
3Indexes10 exercises
4Joins12 exercises
5Sorting and grouping12 exercises

Modules 2 to 5 cost $99 once, for lifetime access. Module 1 is free.

QueryPlan pairs SQL results with SQLite plans so you can check what a change does. Try the free lessons before buying the performance course.

See Modules 2 to 5

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Frequently asked questions

Can I start without SQL experience?

Yes. The free foundations path introduces tables, SELECT, filtering, and sorting in four guided lessons. The SQL performance course assumes you can already write basic queries.

Is QueryPlan video-based?

No. You learn by writing SQL, reading the query plan, and revising your query.

Why SQLite instead of PostgreSQL or MySQL?

SQLite can run real queries in your browser. You can practice identifying table scans, index searches, joins, and temporary sorts. PostgreSQL and MySQL use different plan terms and may choose different plans.

Who is this for?

Start with the free foundations path if you are new to SQL. If you know the basics, the performance course helps you understand indexes, joins, and execution plans.