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50 lines
1.5 KiB
HTML
50 lines
1.5 KiB
HTML
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<p>Table: <code>Views</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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| article_id | int |
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| author_id | int |
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| viewer_id | int |
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| view_date | date |
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+---------------+---------+
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There is no primary key for this table, it may have duplicate rows.
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Each row of this table indicates that some viewer viewed an article (written by some author) on some date.
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Note that equal author_id and viewer_id indicate the same person.
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</pre>
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<p> </p>
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<p>Write an SQL query to find all the authors that viewed at least one of their own articles.</p>
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<p>Return the result table sorted by <code>id</code> in ascending order.</p>
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<p>The query result format is in the following example.</p>
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<p> </p>
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<p><strong>Example 1:</strong></p>
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<pre>
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<strong>Input:</strong>
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Views table:
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+------------+-----------+-----------+------------+
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| article_id | author_id | viewer_id | view_date |
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+------------+-----------+-----------+------------+
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| 1 | 3 | 5 | 2019-08-01 |
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| 1 | 3 | 6 | 2019-08-02 |
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| 2 | 7 | 7 | 2019-08-01 |
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| 2 | 7 | 6 | 2019-08-02 |
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| 4 | 7 | 1 | 2019-07-22 |
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| 3 | 4 | 4 | 2019-07-21 |
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| 3 | 4 | 4 | 2019-07-21 |
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+------------+-----------+-----------+------------+
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<strong>Output:</strong>
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+------+
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| id |
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+------+
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| 4 |
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| 7 |
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+------+
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</pre>
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