每日一题-6（部门工资前三高的所有员工）

题6：

编写一个 SQL 查询，找出每个部门获得前三高工资的所有员工

用窗口函数解决分组和排序的问题
（1）因为涉及到两个表，根据题目要求使用left join连接两表
（2）因为题目要求找出部门薪水前三高的所有员工，因此用dense_rank()函数统计了重复的字段，并且不跳过排序

SELECT Department,Employee,Salary 
from 
(
SELECT 
    b.Name as Department,
    a.Name as Employee,
    a.Salary as Salary,
    DENSE_RANK() over(partition by b.Name order by a.Salary desc) as rank_
from Employee a left join Department b on a.DepartmentId = b.Id
) as t
where rank_ <= 3;