sql找到比manager 工资高的 employee(复制表)

181. Employees Earning More Than Their Managers
要求:找到比manager 工资高的 employee

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

解题:
1.复制表,分别为t1,t2

2.找出两表中id 与 managerid相同,并且雇员工资更高的名字
3. 将name 改为 Employee

select  t1.name  as ‘Employee‘  from

  Employee as t1,

  (select * from Employee) as t2 

  where

    t1.managerid = t2.id

  and

    t1.salary > t2.salary

 

此处需要注意的是:manager 应该是id的直系manager,起初我的思路是找到 ManagerId  is null 的数据,放到 表 t2中,然后继续按照步骤比较两个表中数据,但这就会出现雇员1 可能有 manager1,但是同时manager1 也会有manager2 作为他的manager,这就会导致我表t2中的manager数据有遗漏。导致结果错误。

错误写法:

select  t1.name  as ‘Employee‘  from

  Employee as t1,

  (select * from Employee where managerid is null) as t2 

  where

    t1.managerid = t2.id

  and

    t1.salary > t2.salary

sql找到比manager 工资高的 employee(复制表)

上一篇:mysql 安装默认密码


下一篇:MongoDB介绍