The Employee table holds all employees including their managers. Every employee has an Id, and there is also a column for the manager Id.

    +----+-------+--------+-----------+
    | Id | Name  | Salary | ManagerId |
    +----+-------+--------+-----------+
    | 1  | Joe   | 70000  | 3         |
    | 2  | Henry | 80000  | 4         |
    | 3  | Sam   | 60000  | NULL      |
    | 4  | Max   | 90000  | NULL      |
    +----+-------+--------+-----------+
    Given the Employee table, write a SQL query that finds out employees who earn more than their managers. For the above table, Joe is the only employee who earns more than his manager.

    +----------+
    | Employee |
    +----------+
    | Joe      |
    +----------+

    自連接
        select e.name as 'Employee' 
            from Employee e,Employee m 
                where e.managerid=m.id 
                    and 
                       e.salary>m.salary;
    內連接
        select e.name as Employee 
            from employee e inner join employee m 
                on e.managerid=m.id and e.salary>m.salary;