Q200510-01: 求部门工资最高的员工

问题: 求部门工资最高的员工

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    |

编写一个 SQL 查询，找出每个部门工资最高的员工。例如，根据上述给定的表格，Max 在 IT 部门有最高工资，Henry 在 Sales 部门有最高工资。

+------------+----------+--------+

| Department | Employee | Salary |

+------------+----------+--------+

| IT         | Max      | 90000  |

| Sales      | Henry    | 80000  |

+------------+----------+--------+

解答:

mysql> select d.name as department,b.name as employee,b.salary from (select e.* from employee e inner join
    -> (select max(salary) as max_salary,departmentid from employee group by departmentid) a
    -> on e.salary=a.max_salary and e.departmentid=a.departmentid) b left join department d
    -> on b.departmentid=d.id ;
+------------+----------+--------+
| department | employee | salary |
+------------+----------+--------+
| Sales      | Henry    |  80000 |
| IT         | Max      |  90000 |
+------------+----------+--------+
2 rows in set (0.00 sec)

过程:

create table employee(
    id int,
    name varchar(20) not null,
    salary int,
    departmentid int not null,
    primary key(id))

insert into employee(id,name,salary,departmentid) values ('','Joe','','');
insert into employee(id,name,salary,departmentid) values ('','Henry','','');
insert into employee(id,name,salary,departmentid) values ('','Sam','','');
insert into employee(id,name,salary,departmentid) values ('','Max','','');

create table department(
    id int,
    name varchar(20) not null,
    primary key(id))

insert into department(id,name) values('','IT');
insert into department(id,name) values('','Sales');

select max(salary) as max_salary,departmentid from employee group by departmentid

select e.* from employee e inner join
(select max(salary) as max_salary,departmentid from employee group by departmentid) a
on e.salary=a.max_salary and e.departmentid=a.departmentid

select b.id,b.name,b.salary,d.name from (select e.* from employee e inner join
(select max(salary) as max_salary,departmentid from employee group by departmentid) a
on e.salary=a.max_salary and e.departmentid=a.departmentid) b left join department d
on b.departmentid=d.id 

select d.name as department,b.name as employee,b.salary from (select e.* from employee e inner join
(select max(salary) as max_salary,departmentid from employee group by departmentid) a
on e.salary=a.max_salary and e.departmentid=a.departmentid) b left join department d
on b.departmentid=d.id 

--2020年5月10日 17点22分--

1.       部门工资最高的员工

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    |

编写一个 SQL 查询，找出每个部门工资最高的员工。例如，根据上述给定的表格，Max 在 IT 部门有最高工资，Henry 在 Sales 部门有最高工资。

+------------+----------+--------+

| Department | Employee | Salary |

+------------+----------+--------+

| IT         | Max      | 90000  |

| Sales      | Henry    | 80000  |

+------------+----------+--------+