Employee 表包含所有员工信息，每个员工有其对应的 Id, salary 和 department Id。
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。
| 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 |
| Department | Employee | Salary |
|---|---|---|
| IT | Max | 90000 |
| Sales | Henry | 80000 |
解答
- 子查询获取每个部门最高的工资。
- 再使用 WHERE IN 筛选。
1SELECT
2 d.Name as Department,
3 e.Name as Employee,
4 e.Salary as Salary
5FROM
6 Employee e
7LEFT JOIN
8 Department d
9 ON e.DepartmentId = d.Id
10WHERE (e.DepartmentId, e.Salary) IN (
11 SELECT
12 DepartmentId,
13 MAX(Salary)
14 FROM
15 Employee
16 GROUP BY
17 DepartmentId
18) AND d.Id IS NOT NULL
19ORDER BY e.Id
ORDER BY e.Id是无关紧要的，只是结果集顺序问题。
原题
来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/department-highest-salary
