Table: Views
+---------------+---------+ +| Column Name | Type | ++---------------+---------+ +| article_id | int | +| author_id | int | +| viewer_id | int | +| view_date | date | ++---------------+---------+ +There is no primary key (column with unique values) for this table, the table may have duplicate rows. +Each row of this table indicates that some viewer viewed an article (written by some author) on some date. +Note that equal author_id and viewer_id indicate the same person. ++ +
+ +
Write a solution to find all the authors that viewed at least one of their own articles.
+ +Return the result table sorted by id in ascending order.
The result format is in the following example.
+ ++
Example 1:
+ +Input: +Views table: ++------------+-----------+-----------+------------+ +| article_id | author_id | viewer_id | view_date | ++------------+-----------+-----------+------------+ +| 1 | 3 | 5 | 2019-08-01 | +| 1 | 3 | 6 | 2019-08-02 | +| 2 | 7 | 7 | 2019-08-01 | +| 2 | 7 | 6 | 2019-08-02 | +| 4 | 7 | 1 | 2019-07-22 | +| 3 | 4 | 4 | 2019-07-21 | +| 3 | 4 | 4 | 2019-07-21 | ++------------+-----------+-----------+------------+ +Output: ++------+ +| id | ++------+ +| 4 | +| 7 | ++------+ ++