PostgreSQL: Issues with recursive CTEs returning unexpected results on large datasets
I'm working with PostgreSQL 13 and trying to implement a recursive Common Table Expression (CTE) to fetch hierarchical data from a table... The table structure is as follows: ```sql CREATE TABLE employees ( id SERIAL PRIMARY KEY, name VARCHAR(100), manager_id INT REFERENCES employees(id) ); ``` I want to retrieve all employees that report to a given manager, including their subordinates at all levels. My initial CTE looks like this: ```sql WITH RECURSIVE subordinates AS ( SELECT id, name, manager_id FROM employees WHERE manager_id = $1 UNION ALL SELECT e.id, e.name, e.manager_id FROM employees e INNER JOIN subordinates s ON e.manager_id = s.id ) SELECT * FROM subordinates; ``` I run this query and replace `$1` with the manager's ID. However, on larger datasets, I notice that it returns duplicate entries for some employees. I've also checked that the data does not have any duplicates in the `employees` table. I've tried using the `DISTINCT` keyword in my final SELECT statement, but that didn't help much. The duplicates seem to appear primarily when an employee has multiple managers (which is not the intended design but data inconsistencies occur). To troubleshoot, I added logging to count the number of records in each step of the recursion, and I saw that the CTE was processing rows more than once, which led me to believe the join condition might be the culprit. Does anyone have suggestions on how I can modify my CTE to handle this scenario more effectively? Should I consider using different join types or restructuring the query? Any help would be appreciated!