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 |
+------------+----------+--------+
本题存在以下几个麻烦点：
1、按照部门分类查询工资最高的
2、可能存在多个人会有相同的最高工资
3、部门和员工不对应（这点值得吐槽）
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 //查询最高薪水
ON e1.Salary = e2.`Salary`
AND e1.DepartmentId = e2.`DepartmentId`
WHERE e2.id IS NOT NULL
