MySQL 8.0: implementing Recursive Common Table Expressions in Complex Queries
I'm updating my dependencies and I'm experiencing unexpected results when using Recursive Common Table Expressions (CTEs) in MySQL 8.0. I have a table of employees with a self-referential relationship to represent a hierarchy. My goal is to retrieve all employees under a specific manager, but the results are inconsistent. Here’s the structure of my `employees` table: ```sql CREATE TABLE employees ( id INT PRIMARY KEY, name VARCHAR(100), manager_id INT, FOREIGN KEY(manager_id) REFERENCES employees(id) ); ``` I populated it with some test data: ```sql INSERT INTO employees (id, name, manager_id) VALUES (1, 'Alice', NULL), (2, 'Bob', 1), (3, 'Charlie', 1), (4, 'David', 2), (5, 'Eve', 2); ``` I wrote a CTE to fetch all employees under Alice (id = 1): ```sql WITH RECURSIVE employee_hierarchy 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 employee_hierarchy eh ON e.manager_id = eh.id ) SELECT * FROM employee_hierarchy; ``` However, the output only shows Bob and Charlie without David and Eve, who should also be included since they are both under Bob. I double-checked the data and the logic, and everything seems correct. I also tried adding a condition to check for `manager_id = 1` in the second part of the CTE, but it didn’t help. I'm getting the following behavior message occasionally when testing different variations: `behavior Code: 1242. Subquery returns more than 1 row`. I suspect this might be related to how MySQL handles recursive queries or my usage of joins. Has anyone encountered similar issues with recursive CTEs in MySQL 8.0? What could be the reason for these unexpected results, and how can I correctly retrieve all employees under a specific manager? This is happening in both development and production on Linux. Hoping someone can shed some light on this.