每日一题-5（部门工资最高的员工）

题5：

根据下面两个表编写一个 SQL 查询，找出每个部门工资最高的员工。


方法一：窗口函数
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）用rank（）函数根据部门分组和薪水降序排序

select Department, Employee, Salary
from 
(
select 
    b.Name as Department, 
    a.Name as Employee, 
    a.Salary as Salary, 
    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_ = 1;

方法二：
（1）用左连接连接两表
（2）找出每个部门内最高的工资作为子查询从而确定查询的条件

SELECT
    b.name AS Department,
    a.name AS Employee,
    Salary
FROM
    Employee as a 
        left join
    Department as b ON a.DepartmentId = b.Id
WHERE
    (a.DepartmentId , Salary) IN
    (   SELECT
            DepartmentId, MAX(Salary)
        FROM
            Employee
        GROUP BY DepartmentId
	)
;