EASY

Author: evanmathew

1148. Article Views I.sql

@@ -1,3 +1,57 @@
-select DISTINCT author_id AS id from Views 
-where viewer_id = author_id
-order by author_id asc
+-- Problem:
+
+/*
+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    |
++------+
+*/
+
+-------------------------------------------------------------------------------
+
+-- Solution:
+
+SELECT DISTINCT author_id AS id FROM Views 
+WHERE viewer_id = author_id
+ORDER BY author_id ASC