SQL

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

题解：先查询每个部门的最高工资

SELECT DepartmentId, MAX(Salary) FROM Employee
GROUP BY DepartmentId 

由于可能存在工资相同的不同雇员，使用IN语句取出满足工资等于最高工资的雇员

SELECT d.Name AS Department, e.Name AS Employee, e.Salary FROM Employee e JOIN Department d  
ON e.DepartmentId = d.Id
WHERE 
(d.Id,e.Salary) IN 
(SELECT DepartmentId, MAX(Salary) FROM Employee
GROUP BY DepartmentId )

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/department-highest-salary
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