Employee 表包含所有員工資訊，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資訊。

+----+----------+
| 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  |

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

剛開始不知道咋想的，想著兩個表先聯一下，然後對id group by，好像想亂了，吃飯回來發現其實兩個表聯一下，只要ID相等，然後找最大的薪水就行了，語句如下：

select b.Name as Department ,a.Name as Employee ,a.Salary as Salary from Employee a,Department b where a.DepartmentId=b.Id
and a.Salary=(select max(Salary) from Employee where DepartmentId=b.Id)