mysql 自连接但是不连接本身

CREATE TABLE employees (
    id INT PRIMARY KEY,
    name VARCHAR(100),
    manager_id INT
);

SELECT 
    e1.name AS employee_name,
    e2.name AS manager_name
FROM 
    employees e1
JOIN 
    employees e2 ON e1.manager_id = e2.id
WHERE 
    e1.name = 'John Doe';

SELECT DISTINCT 
    e1.name AS employee_name,
    e2.name AS manager_name
FROM 
    employees e1
JOIN 
    employees e2 ON e1.manager_id = e2.id
WHERE 
    e1.name = 'John Doe';

SELECT 
    e1.name AS employee_name,
    (
        SELECT e2.name 
        FROM employees e2 
        WHERE e1.manager_id = e2.id
    ) AS manager_name
FROM 
    employees e1
WHERE 
    e1.name = 'John Doe';