Leetcode 181. Employees Earning More Than Their Managers (Database)

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)