Article Views I
Problem Statement - link #
SQL Schema
Create table If Not Exists Views (article_id int, author_id int, viewer_id int, view_date date)
Truncate table Views
insert into Views (article_id, author_id, viewer_id, view_date) values ('1', '3', '5', '2019-08-01')
insert into Views (article_id, author_id, viewer_id, view_date) values ('1', '3', '6', '2019-08-02')
insert into Views (article_id, author_id, viewer_id, view_date) values ('2', '7', '7', '2019-08-01')
insert into Views (article_id, author_id, viewer_id, view_date) values ('2', '7', '6', '2019-08-02')
insert into Views (article_id, author_id, viewer_id, view_date) values ('4', '7', '1', '2019-07-22')
insert into Views (article_id, author_id, viewer_id, view_date) values ('3', '4', '4', '2019-07-21')
insert into Views (article_id, author_id, viewer_id, view_date) values ('3', '4', '4', '2019-07-21')
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.
Your Task:
Write an SQL query 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 query result format is in the following example.
Example #
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 |
+------+
Solutions #
-- Write your T-SQL query statement below
select distinct author_id as id from views where author_id=viewer_id order by id
;