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 | ±-----------±---------±-------+
因为 Employee 表包含 Salary 和 DepartmentId 字段， 我们可以以此在部门内查询最高工资。 然后，我们可以把表 Employee 和 Department 连接， 再在这张临时表里用 IN 语句查询部门名字和工资的关系。 SELECT Department.name AS 'Department', Employee.name AS 'Employee', Salary FROM Employee JOIN Department ON Employee.DepartmentId = Department.Id WHERE (Employee.DepartmentId , Salary) IN ( SELECT DepartmentId, MAX(Salary) FROM Employee GROUP BY DepartmentId )链接：https://leetcode-cn.com/problems/department-highest-salary/solution/bu-men-gong-zi-zui-gao-de-yuan-gong-by-leetcode/
