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74 lines
2.2 KiB
HTML
74 lines
2.2 KiB
HTML
<p>项目表 <code>Project</code>： </p>
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<pre>
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+-------------+---------+
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| Column Name | Type |
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+-------------+---------+
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| project_id | int |
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| employee_id | int |
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+-------------+---------+
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主键为 (project_id, employee_id)。
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employee_id 是员工表 <code>Employee 表的外键。</code>
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这张表的每一行表示 employee_id 的员工正在 project_id 的项目上工作。
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</pre>
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<p> </p>
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<p>员工表 <code>Employee</code>：</p>
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<pre>
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+------------------+---------+
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| Column Name | Type |
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+------------------+---------+
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| employee_id | int |
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| name | varchar |
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| experience_years | int |
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+------------------+---------+
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主键是 employee_id。数据保证 experience_years 非空。
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这张表的每一行包含一个员工的信息。</pre>
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<p> </p>
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<p>请写一个 SQL 语句，查询每一个项目中员工的 <strong>平均 </strong>工作年限，<strong>精确到小数点后两位</strong>。</p>
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<p>以 <strong>任意</strong> 顺序返回结果表。</p>
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<p>查询结果的格式如下。</p>
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<p> </p>
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<p><strong>示例 1:</strong></p>
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<pre>
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<strong>输入：</strong>
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Project 表：
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+-------------+-------------+
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| project_id | employee_id |
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+-------------+-------------+
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| 1 | 1 |
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| 1 | 2 |
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| 1 | 3 |
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| 2 | 1 |
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| 2 | 4 |
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+-------------+-------------+
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Employee 表：
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+-------------+--------+------------------+
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| employee_id | name | experience_years |
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+-------------+--------+------------------+
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| 1 | Khaled | 3 |
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| 2 | Ali | 2 |
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| 3 | John | 1 |
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| 4 | Doe | 2 |
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+-------------+--------+------------------+
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<strong>输出：</strong>
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+-------------+---------------+
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| project_id | average_years |
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+-------------+---------------+
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| 1 | 2.00 |
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| 2 | 2.50 |
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+-------------+---------------+
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<strong>解释：</strong>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
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</pre>
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