PostgreSQL: advanced patterns when using CTE with ORDER BY and LIMIT in recursive queries
I'm migrating some code and I can't seem to get I've spent hours debugging this and I'm working with an scenario with a recursive Common Table Expression (CTE) in PostgreSQL 13.3 where the results are not ordered as I expected when I apply an `ORDER BY` clause along with a `LIMIT`. Here’s the scenario: I'm trying to retrieve the first 10 rows from a tree structure representing hierarchical data, but the ordering seems to be disregarded after the recursion. I have the following CTE: ```sql WITH RECURSIVE org_chart AS ( SELECT id, name, manager_id FROM employees WHERE manager_id IS NULL UNION ALL SELECT e.id, e.name, e.manager_id FROM employees e INNER JOIN org_chart o ON e.manager_id = o.id ) SELECT * FROM org_chart ORDER BY name LIMIT 10; ``` When I run this query, I expect to see the first 10 employees sorted by their names. However, it looks like the results are returning the full tree structure but only the first 10 entries based on the initial order before the `ORDER BY` clause. I’ve tried moving the `ORDER BY` into the inner CTE, as well as adjusting the `LIMIT`, but I still encounter the same scenario. Here’s the alternative query I tested: ```sql WITH RECURSIVE org_chart AS ( SELECT id, name, manager_id FROM employees WHERE manager_id IS NULL UNION ALL SELECT e.id, e.name, e.manager_id FROM employees e INNER JOIN org_chart o ON e.manager_id = o.id ORDER BY e.name ) SELECT * FROM org_chart LIMIT 10; ``` Unfortunately, this results in a syntax behavior. I have also consulted the PostgreSQL documentation regarding CTEs, but I couldn't find any specific mention of ordering in recursive queries. Does anyone know the correct way to enforce the ordering in this context? Any insights or best practices would be greatly appreciated! I'd love to hear your thoughts on this. Is this even possible? Has anyone dealt with something similar?