Sequential CTEs.

You can list several CTEs separated by commas under one WITH: WITH a AS (...), b AS (...) SELECT .... Each later CTE may read the earlier ones by name, so the query becomes a chain of small steps: summarize → filter → join.

Rule: a comma between CTEs, but NOT before the main SELECT. Definition order matters — a CTE can only use ones defined before it.

A small step is easy to check: temporarily replace the main SELECT with SELECT * FROM step and look at the intermediate result.

Common mistakes: a comma before the main SELECT; repeating WITH for the second CTE; referring to a CTE defined further down; too many columns in intermediate steps.

Small example:

WITH a AS (SELECT customer_id, COUNT(*) AS n FROM orders GROUP BY customer_id), b AS (SELECT customer_id FROM a WHERE n >= 2) SELECT COUNT(*) AS repeat_customers FROM b;