👀 Views: 0 💬 Answers: 1 📅 Created: 2025-06-15

mysql cte recursive hierarchical-data sql

I'm working on a project and hit a roadblock. I'm facing an issue with a recursive Common Table Expression (CTE) in MySQL 8.0 where it's returning incorrect results for hierarchical data. I have a table called `employees` that represents an organizational structure with fields `id`, `name`, and `manager_id`. The CTE is supposed to return a list of employees along with their respective hierarchy levels. However, when I run my query, it seems to be skipping some employees and showing incorrect hierarchy levels. Here's the relevant portion of my query: ```sql WITH RECURSIVE employee_hierarchy AS ( SELECT id, name, manager_id, 0 AS level FROM employees WHERE manager_id IS NULL 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; ``` Initially, I expected the output to list all employees with their correct levels, but I noticed that some employees who report to managers are missing from the result set. I also tried adjusting the base case of the CTE to select employees directly reporting to a specific manager, but that didn't change the outcome. Additionally, I checked for circular references in the `employees` table, but there don't appear to be any. I also tried using `DISTINCT` to eliminate duplicates, but that didn't resolve the issue. The output for some employees shows their levels incorrectly as `NULL` or skips them altogether. Has anyone encountered something similar or have insights on how to properly construct a recursive CTE for hierarchical data in MySQL 8.0? What might be causing the CTE to behave this way? For context: I'm using Sql on macOS.