mysql中的level

CREATE TABLE employees (
    id INT PRIMARY KEY,
    name VARCHAR(255),
    manager_id INT
);

WITH RECURSIVE org_tree AS (
    SELECT id, name, manager_id, 1 AS level
    FROM employees
    WHERE manager_id IS NULL
    UNION ALL
    SELECT e.id, e.name, e.manager_id, ot.level + 1
    FROM employees e
    JOIN org_tree ot ON e.manager_id = ot.id
)
SELECT * FROM org_tree;

WITH RECURSIVE org_tree AS (
    SELECT id, name, manager_id, 1 AS level
    FROM employees
    WHERE manager_id IS NULL
    UNION ALL
    SELECT e.id, e.name, e.manager_id, ot.level + 1
    FROM employees e
    JOIN org_tree ot ON e.manager_id = ot.id
    WHERE NOT EXISTS (
        SELECT 1
        FROM org_tree ot2
        WHERE ot2.id = e.id
    )
)
SELECT * FROM org_tree;