4. Find Customer Referee

Problem

https://leetcode.com/problems/article-views-i/description/?envType=study-plan-v2&envId=top-sql-50

Solution

select distinct author_id as id
from Views
where viewer_id = author_id
order by author_id

Find all authors who viewd their own article at least once, where input has at least one pair of same viewer_id and author_id