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

本題存在以下幾個麻煩點： 1、按照部門分類查詢工資最高的 2、可能存在多個人會有相同的最高工資 3、部門和員工不對應（這點值得吐槽）

SELECT
  d.Name AS Department,
  e2.Name AS Employee,
  e2.Salary AS Salary
FROM
  Department d
  LEFT JOIN employee e2
    ON e2.departmentId = d.id
  RIGHT JOIN
    (SELECT
      e.DepartmentId,
      MAX(e.`Salary`) AS salary
    FROM
      employee e
    GROUP BY e.`DepartmentId`) e1 //查詢最高薪水
    ON e1.Salary = e2.`Salary`
    AND e1.DepartmentId = e2.`DepartmentId`
WHERE e2.id IS NOT NULL