2022-03-27 20:56:26 +08:00
|
|
|
|
<p>表: <code>Employee</code></p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
|
|
|
|
+--------------+---------+
|
|
|
|
|
| 列名 | 类型 |
|
|
|
|
|
+--------------+---------+
|
|
|
|
|
| id | int |
|
|
|
|
|
| name | varchar |
|
|
|
|
|
| salary | int |
|
|
|
|
|
| departmentId | int |
|
|
|
|
|
+--------------+---------+
|
2023-12-09 18:42:21 +08:00
|
|
|
|
在 SQL 中,id是此表的主键。
|
|
|
|
|
departmentId 是 Department 表中 id 的外键(在 Pandas 中称为 join key)。
|
|
|
|
|
此表的每一行都表示员工的 id、姓名和工资。它还包含他们所在部门的 id。
|
2022-03-27 20:56:26 +08:00
|
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p> </p>
|
|
|
|
|
|
|
|
|
|
<p>表: <code>Department</code></p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
|
|
|
|
+-------------+---------+
|
|
|
|
|
| 列名 | 类型 |
|
|
|
|
|
+-------------+---------+
|
|
|
|
|
| id | int |
|
|
|
|
|
| name | varchar |
|
|
|
|
|
+-------------+---------+
|
2023-12-09 18:42:21 +08:00
|
|
|
|
在 SQL 中,id 是此表的主键列。
|
|
|
|
|
此表的每一行都表示一个部门的 id 及其名称。
|
2022-03-27 20:56:26 +08:00
|
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p> </p>
|
|
|
|
|
|
2023-12-09 18:42:21 +08:00
|
|
|
|
<p>查找出每个部门中薪资最高的员工。<br />
|
2022-03-27 20:56:26 +08:00
|
|
|
|
按 <strong>任意顺序</strong> 返回结果表。<br />
|
|
|
|
|
查询结果格式如下例所示。</p>
|
|
|
|
|
|
|
|
|
|
<p> </p>
|
|
|
|
|
|
|
|
|
|
<p><strong>示例 1:</strong></p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
|
|
|
|
<b>输入:</b>
|
|
|
|
|
Employee 表:
|
|
|
|
|
+----+-------+--------+--------------+
|
|
|
|
|
| id | name | salary | departmentId |
|
|
|
|
|
+----+-------+--------+--------------+
|
|
|
|
|
| 1 | Joe | 70000 | 1 |
|
|
|
|
|
| 2 | Jim | 90000 | 1 |
|
|
|
|
|
| 3 | Henry | 80000 | 2 |
|
|
|
|
|
| 4 | Sam | 60000 | 2 |
|
|
|
|
|
| 5 | Max | 90000 | 1 |
|
|
|
|
|
+----+-------+--------+--------------+
|
|
|
|
|
Department 表:
|
|
|
|
|
+----+-------+
|
|
|
|
|
| id | name |
|
|
|
|
|
+----+-------+
|
|
|
|
|
| 1 | IT |
|
|
|
|
|
| 2 | Sales |
|
|
|
|
|
+----+-------+
|
|
|
|
|
<b>输出:</b>
|
|
|
|
|
+------------+----------+--------+
|
|
|
|
|
| Department | Employee | Salary |
|
|
|
|
|
+------------+----------+--------+
|
|
|
|
|
| IT | Jim | 90000 |
|
|
|
|
|
| Sales | Henry | 80000 |
|
|
|
|
|
| IT | Max | 90000 |
|
|
|
|
|
+------------+----------+--------+
|
|
|
|
|
<strong>解释:</strong>Max 和 Jim 在 IT 部门的工资都是最高的,Henry 在销售部的工资最高。</pre>
|