dequery: Deconstruct your SQL, step by step

dequery shows how a SQL query really runs. Each clause becomes a step in execution order (FROM, JOIN, WHERE, GROUP BY, HAVING, SELECT, ORDER BY, LIMIT), with the rows it received, the rows it kept, and why the others were dropped.

• Learn SQL execution order with 36 short lessons, from joins and NULL to window functions and recursive CTEs.
• Debug queries that run but return the wrong numbers, and follow one row to the step where it disappears.
• Catch common mistakes: a JOIN that multiplies rows before a SUM, a WHERE that turns a LEFT JOIN into an INNER JOIN, NOT IN against a NULL, LIMIT without ORDER BY.
• Use your own CSV, JSON or Parquet files. It runs in the browser on DuckDB, so your data stays on your machine.