181. Employees Earning More Than Their Managers
2017-08-29 10:16
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题目:
Employee表中有所有雇员及其它们的管理者。每一个员工都有他自己的
Id,同时还有一列数据记录了他们管理者的
Id。
表
Employee
Id | Name | Salary | ManagerId |
---|---|---|---|
1 | Joe | 70000 | 3 |
2 | Henry | 80000 | 4 |
3 | Sam | 60000 | NULL |
4 | Max | 90000 | NULL |
salary比他对应的管理者的薪水高的雇员姓名。
例如:
Joe的薪水是70000他的管理者
Id是3,即为
Sam(薪水60000,小与其雇员的70000薪水)因此,输出
Joe。
Employee |
---|
Joe |
解析:
题目中涉及表内的连接(Id和
ManagerId)与比较(
Salary之间的比较 )。因此,首先要想到创造一个表的自连接。由表
Employee连接到自身,然后做不同的命名。这样就和两张表连接和检索的情况很类似了。
select e1 name as Employee from employee as e1 join employee as e2 where e2.id=e1.managerId and e1.salary>e2.salary
注意连接的方向,一定得是
managerId连接
Id,因为有些
Id是没有
managerId
这里注意,第一行一定要写
as Employee因为题目中最后输出的表头是
Employee。
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