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 |
+----------+
思路：考虑同一个table Employee的两个copy e1 和 e2。Where 里面可以用AND。在一个table中根据一些条件选出一部分内容，如果这个条件牵扯到table里的其他row，那么往往使用select from table的多个copy。
# Write your MySQL query statement below
select e1.Name as Employee
from Employee as e1, Employee as e2
where e1.Salary > e2.Salary and e1.ManagerId=e2.Id)