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56 lines
2.1 KiB
HTML
56 lines
2.1 KiB
HTML
<p>活动记录表：<code>Activity</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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| user_id | int |
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| session_id | int |
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| activity_date | date |
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| activity_type | enum |
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+---------------+---------+
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该表是用户在社交网站的活动记录。
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该表没有主键，可能包含重复数据。
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activity_type 字段为以下四种值 ('open_session', 'end_session', 'scroll_down', 'send_message')。
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每个 session_id 只属于一个用户。
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</pre>
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<p> </p>
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<p>请写SQL查询出截至 <code>2019-07-27</code>（包含2019-07-27），近<strong> </strong><code>30</code> 天的每日活跃用户数（当天只要有一条活动记录，即为活跃用户）。</p>
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<p>以 <strong>任意顺序</strong> 返回结果表。</p>
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<p>查询结果示例如下。</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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Activity table:
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+---------+------------+---------------+---------------+
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| user_id | session_id | activity_date | activity_type |
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+---------+------------+---------------+---------------+
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| 1 | 1 | 2019-07-20 | open_session |
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| 1 | 1 | 2019-07-20 | scroll_down |
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| 1 | 1 | 2019-07-20 | end_session |
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| 2 | 4 | 2019-07-20 | open_session |
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| 2 | 4 | 2019-07-21 | send_message |
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| 2 | 4 | 2019-07-21 | end_session |
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| 3 | 2 | 2019-07-21 | open_session |
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| 3 | 2 | 2019-07-21 | send_message |
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| 3 | 2 | 2019-07-21 | end_session |
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| 4 | 3 | 2019-06-25 | open_session |
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| 4 | 3 | 2019-06-25 | end_session |
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+---------+------------+---------------+---------------+
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<strong>输出：</strong>
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+------------+--------------+
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| day | active_users |
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+------------+--------------+
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| 2019-07-20 | 2 |
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| 2019-07-21 | 2 |
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+------------+--------------+ <strong>
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解释：</strong>注意非活跃用户的记录不需要展示。</pre>
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