SQL reference by task and query stage

A task-oriented reference for clauses, predicates, joins, aggregation, windows, transactions, constraints, and basic plan reasoning.

This public page is designed to answer the learning question directly and then point to the interactive workspace only when practice is useful.

Browse syntax by query stage: projection, filtering, grouping, joining, set operations, windows, data changes, constraints, transactions, and plan reasoning.

Browse by task: choose rows, shape columns, combine tables, aggregate safely, compare periods, preserve null behavior, and debug cardinality.

Browse by skill family so reference pages connect back to lessons, glossary concepts, and original worked examples.

The links below are canonical public resources. They render as normal anchors and do not require the product runtime.

Public pages explain concepts and show verified examples. The `/app` workspace adds the editor, PGlite worker, hidden variants, drafts, review scheduling, and mastery evidence.