Employee 表包含所有員工信息，每個員工有其對應的 Id, salary 和 department Id。
編寫一個 SQL 查詢，找出每個部門工資最高的員工。例如，根據上述給定的表格，Max 在 IT 部門有最高工資，Henry 在 Sales 部門有最高工資。
| Id | Name | Salary | DepartmentId |
|---|---|---|---|
| 1 | Joe | 70000 | 1 |
| 2 | Henry | 80000 | 2 |
| 3 | Sam | 60000 | 2 |
| 4 | Max | 90000 | 1 |
Department 表包含公司所有部門的信息。
| Id | Name |
|---|---|
| 1 | IT |
| 2 | Sales |
| Department | Employee | Salary |
|---|---|---|
| IT | Max | 90000 |
| Sales | Henry | 80000 |
解答
- 子查詢獲取每個部門最高的工資。
- 再使用 WHERE IN 篩選。
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是無關緊要的，只是結果集順序問題。
原題
來源：力扣（LeetCode）
鏈接：https://leetcode-cn.com/problems/department-highest-salary
