SQL 184. 部门工资最高的员工

题目：

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 | Henry | 80000 | 2 |
| 3 | Sam | 60000 | 2 |
| 4 | Max | 90000 | 1 |
±—±------±-------±-------------+
Department 表包含公司所有部门的信息。

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

Create table If Not Exists Employee (Idint, Name varchar(255), Salary int, DepartmentId int);
Create table If Not Exists Department (Idint, Name varchar(255));
Truncate table Employee;
insert into Employee (Id, Name, Salary,DepartmentId) values ('1', 'Joe', '70000', '1');
insert into Employee (Id, Name, Salary,DepartmentId) values ('2', 'Henry', '80000', '2');
insert into Employee (Id, Name, Salary,DepartmentId) values ('3', 'Sam', '60000', '2');
insert into Employee (Id, Name, Salary,DepartmentId) values ('4', 'Max', '90000', '1');
Truncate table Department;
insert into Department (Id, Name) values('1', 'IT');
insert into Department (Id, Name) values('2', 'Sales');

答案1

参考：https://blog.csdn.net/wal1314520/article/details/80108191

不是很能理解为啥e2.DepartmentId =e1.Department就可以了

select d.Name Department ,e1.Name Employee,e1.Salary Salary 
from Employee e1
inner join Department d on e1.DepartmentId= d.Id
where e1.Salary in (select Max(e2.Salary) from Employee e2 where e2.DepartmentId =e1.DepartmentId)

答案2

select d.Name as Department,e1.Name as Employee,e1.Salary as Salary
from Employee e1 , Department d
where e1.DepartmentId=d.Id  and (e1.Salary,e1.DepartmentId) 
in (select max(Salary),DepartmentId from Employee group by DepartmentId)