sql 184. 部門工資最高的員工

Employee 表包含所有員工信息，每個員工有其對應的 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 表包含公司所有部門的信息。

+----+----------+
| Id | Name |
+----+----------+
| 1 | IT |
| 2 | Sales |
+----+----------+
編寫一個 SQL 查詢，找出每個部門工資最高的員工。例如，根據上述給定的表格，Max 在 IT 部門有最高工資，Henry 在 Sales 部門有最高工資。

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

 

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

此次學到的用法為把查詢到的結果當做另一次查詢的條件

另一個答案為

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

由此答案可得出select后的結果可給別的select當源，但個數必須匹配