[MySQL][LeetCode][Easy] 181. Employees Earning More Than Their Managers

心得：

題目要求找出有哪些人的薪水比主管高，找出名字並修改欄位名稱為Employee。

題目：

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      |
+----------+

答案：

1. Sub Select

   # Write your MySQL query statement below
   SELECT  a.Name AS Employee
   FROM    Employee AS a
   WHERE   a.Salary > (SELECT  z.Salary 
                       FROM    Employee AS z
                       WHERE   z.Id = a.ManagerId);

2. Join

   # Write your MySQL query statement below
   SELECT  a.Name AS Employee
   FROM    Employee AS a
   JOIN    Employee AS b
   ON      a.ManagerId = b.Id
   WHERE   a.Salary > b.Salary

3. From

   # Write your MySQL query statement below
   SELECT  a.Name AS Employee
   FROM    Employee AS a, Employee AS b
   WHERE   a.ManagerId = b.Id
   AND     a.Salary > b.Salary