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leetcode-cn/problem (Chinese)/项目员工 I [project-employees-i].html

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+<p>项目表&nbsp;<code>Project</code>：&nbsp;</p>
+
+<pre>
++-------------+---------+
+| Column Name | Type    |
++-------------+---------+
+| project_id  | int     |
+| employee_id | int     |
++-------------+---------+
+主键为 (project_id, employee_id)。
+employee_id 是员工表 <code>Employee 表的外键。</code>
+</pre>
+
+<p>员工表&nbsp;<code>Employee</code>：</p>
+
+<pre>
++------------------+---------+
+| Column Name      | Type    |
++------------------+---------+
+| employee_id      | int     |
+| name             | varchar |
+| experience_years | int     |
++------------------+---------+
+主键是 employee_id。
+</pre>
+
+<p>&nbsp;</p>
+
+<p>请写一个 SQL&nbsp;语句，查询每一个项目中员工的&nbsp;<strong>平均&nbsp;</strong>工作年限，<strong>精确到小数点后两位</strong>。</p>
+
+<p>查询结果的格式如下：</p>
+
+<pre>
+Project 表：
++-------------+-------------+
+| project_id  | employee_id |
++-------------+-------------+
+| 1           | 1           |
+| 1           | 2           |
+| 1           | 3           |
+| 2           | 1           |
+| 2           | 4           |
++-------------+-------------+
+
+Employee 表：
++-------------+--------+------------------+
+| employee_id | name   | experience_years |
++-------------+--------+------------------+
+| 1           | Khaled | 3                |
+| 2           | Ali    | 2                |
+| 3           | John   | 1                |
+| 4           | Doe    | 2                |
++-------------+--------+------------------+
+
+Result 表：
++-------------+---------------+
+| project_id  | average_years |
++-------------+---------------+
+| 1           | 2.00          |
+| 2           | 2.50          |
++-------------+---------------+
+第一个项目中，员工的平均工作年限是 (3 + 2 + 1) / 3 = 2.00；第二个项目中，员工的平均工作年限是 (3 + 2) / 2 = 2.50
+</pre>