_1148.sql

--1148. Article Views I
--
--Table: Views
--
--+---------------+---------+
--| Column Name   | Type    |
--+---------------+---------+
--| article_id    | int     |
--| author_id     | int     |
--| viewer_id     | int     |
--| view_date     | date    |
--+---------------+---------+
--There is no primary key for this table, it 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 an SQL query to find all the authors that viewed at least one of their own articles, sorted in ascending order by their id.
--
--The query result format is in the following example:
--
--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 |
--+------------+-----------+-----------+------------+
--
--Result table:
--+------+
--| id   |
--+------+
--| 4    |
--| 7    |
--+------+

--# Write your MySQL query statement below
select distinct(author_id) as id from Views where author_id = viewer_id order by id asc;