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[LeetCode] 184.Department Highest Salary 系里最高薪水
The Employee table holds all employees. Every employee has an Id, a salary, and there is also a column for the department Id.
+----+-------+--------+--------------+
| Id | Name | Salary | DepartmentId |
+----+-------+--------+--------------+
| 1 | Joe | 70000 | 1 |
| 2 | Henry | 80000 | 2 |
| 3 | Sam | 60000 | 2 |
| 4 | Max | 90000 | 1 |
+----+-------+--------+--------------+
The Department table holds all departments of the company.
+----+----------+
| Id | Name |
+----+----------+
| 1 | IT |
| 2 | Sales |
+----+----------+
Write a SQL query to find employees who have the highest salary in each of the departments. For the above tables, Max has the highest salary in the IT department and Henry has the highest salary in the Sales department.
+------------+----------+--------+
| Department | Employee | Salary |
+------------+----------+--------+
| IT | Max | 90000 |
| Sales | Henry | 80000 |
+------------+----------+--------+
这道题让给了我们两张表，Employee表和Department表，让我们找系里面薪水最高的人的，实际上这题是Second Highest Salary和Combine Two Tables的结合题，我们既需要联合两表，又要找到最高薪水，那么我们首先让两个表内交起来，然后将结果表需要的列都标明，然后就是要找最高的薪水，我们用Max关键字来实现，参见代码如下：
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数据库系统概念 第6版
本书主要讲述了数据模型、基于对象的数据库和XML、数据存储和查询、事务管理、体系结构等方面的内容。
