部门工资最高的员工（求组内最大值）

https://leetcode-cn.com/problems/department-highest-salary/

求组内最大值，可以不使用exist，in前面可以用的多个字段筛选。

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
	)
;