Fraudulent Upvotes

'''
We’re given three tables representing a forum of users and their comments on posts.

We want to figure out if users are creating multiple accounts to upvote their own comments.

What kind of metrics could we use to figure this out?

Write a query that could display the percentage of users on our forum that would be acting fraudulently in this manner. 
'''


SELECT 
a.voter_id

 from(
select cv.user_id as voter_id, 
c.user_id as commenter_id,
c.id as comment_id
from comment_votes cv inner join comments c on 
cv.comment_id=c.id
where is_upvote='True')a

where a.voter_id in (

    select comment_votes.user_id
    from comment_votes left join comments on 
    comment_votes.user_id = comments.user_id
    where comments.id is null and is_upvote='True'
)
group by a.voter_id

having count(distinct commenter_id) = 1 and count(distinct comment_id)>3