部门中工资最高的员工

184. 部门工资最高的员工

难度中等271

SQL架构

Employee 表包含所有员工信息，每个员工有其对应的 Id, salary 和 department Id。

+----+-------+--------+--------------+
| Id | Name  | Salary | DepartmentId |
+----+-------+--------+--------------+
| 1  | Joe   | 70000  | 1            |
| 2  | Jim   | 90000  | 1            |
| 3  | Henry | 80000  | 2            |
| 4  | Sam   | 60000  | 2            |
| 5  | Max   | 90000  | 1            |
+----+-------+--------+--------------+

Department 表包含公司所有部门的信息。

+----+----------+
| Id | Name     |
+----+----------+
| 1  | IT       |
| 2  | Sales    |
+----+----------+

编写一个 SQL 查询，找出每个部门工资最高的员工。对于上述表，您的 SQL 查询应返回以下行（行的顺序无关紧要）。

+------------+----------+--------+
| Department | Employee | Salary |
+------------+----------+--------+
| IT         | Max      | 90000  |
| IT         | Jim      | 90000  |
| Sales      | Henry    | 80000  |
+------------+----------+--------+

解释：

Max 和 Jim 在 IT 部门的工资都是最高的，Henry 在销售部的工资最高。

 

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错误的代码：   用的 left  join         有可能会出现null的情况

select Department.Name Department,Employee.Name Employee , Salary
    left join Department as d on Employee.DepartmentId=Department.Id
        where d.DepartmentId,d.Salary    
            (select DepartmentId,max(Salary) from Employee group by DepartmentId)

正确的代码：用的 join

select d.Name Department,e.Name Employee , Salary
    from Employee e
        join Department as d on e.DepartmentId=d.Id
            where (e.DepartmentId,e.Salary) in   
                (select DepartmentId,max(Salary) from Employee group by DepartmentId)