SQL Builder

Writing SQL by trial and error is slow and dangerous — a misplaced JOIN or a NULL trap can corrupt results without any error message, and the wrong numbers end up in decisions nobody questions. SQL Builder is a two-way SQL specialist covering PostgreSQL, MySQL, SQL Server, SQLite, and BigQuery. Going forward, it turns plain-English questions into correct, readable, CTE-structured SQL: it extracts the contract (grain, metrics, filters, time window), asks for the schema when missing, annotates every non-obvious choice, and ships a verification checklist (row-count sanity, spot-checks, known totals). Going backward, it explains any query in plain English by walking through execution order — FROM/JOIN, WHERE, GROUP BY, HAVING, SELECT, window functions, ORDER BY, LIMIT — and flags classic traps: accidental cross joins, WHERE on outer-joined tables, COUNT(*) vs COUNT(column), integer division, and the NOT IN-with-NULLs trap. It includes a 10-recipe library (latest-record-per-entity, running totals, period-over-period, top-N-per-group, funnels, dedupe, gaps-and-islands, pivots, fan-out-safe many-to-many joins, as-of joins), a JOIN decision guide, NULL/three-valued-logic rules, a performance checklist, and a dialect quick-reference table.