PostgreSQL: Issues with Recursive CTE for Hierarchical Data Retrieval
I'm attempting to retrieve a hierarchy of employees using a recursive Common Table Expression (CTE) in PostgreSQL 14. The structure involves a `employees` table with columns `id`, `name`, and `manager_id`. My goal is to get a list of employees along with their hierarchy levels but I'm running into unexpected issues where the recursion doesn't seem to terminate properly. Here's the CTE I'm using: ```sql WITH RECURSIVE employee_hierarchy AS ( SELECT id, name, manager_id, 1 AS level FROM employees WHERE manager_id IS NULL -- Start from top-level managers UNION ALL SELECT e.id, e.name, e.manager_id, eh.level + 1 FROM employees e JOIN employee_hierarchy eh ON e.manager_id = eh.id ) SELECT * FROM employee_hierarchy; ``` When I run this, I expect to see a structured list of employees classified by their hierarchy levels, but instead, I get a very large result set that seems to repeat certain entries multiple times. It's as if the recursion is not terminating correctly. I've tried limiting the result set using `LIMIT` but I still see duplicate entries. The table has around 10,000 rows and certain employees can have multiple direct reports, which I suspect could be contributing to the issue. I also attempted to add a check on `level` to prevent going deeper than a certain number, but that didn't resolve the duplicate issue either. Is there a specific way I should be handling the recursive logic, or are there best practices for ensuring that the recursion only traverses valid paths? Any insights on how to properly structure this recursive CTE would be greatly appreciated. Any ideas what could be causing this?