MySQL - Limit Field To 5 Maximum Occurrences - mysql

Question

Background:
I run a platform which allows users to follow creators and view their content.
The following query successfully displays 50 posts ordered by popularity. There is also some other logic to not show posts the user has already saved/removed, but that is not relevant for this question.
Problem:
If one creator is particularly popular (high popularity), the top 50 posts returned will nearly all be by that creator.
This skews the results as ideally the 50 posts returned will not be in favor of one particular author.
Question:
How can I limit it so the author (which uses the field posted_by) is returned no more than 5 times. It could be less, but definitely no more than 5 times should one particular author be returned.
It should still be finally ordered by popularity DESC
SELECT *
FROM `source_posts`
WHERE `posted_by` IN (SELECT `username`
FROM `source_accounts`
WHERE `id` IN (SELECT `sourceid`
FROM `user_source_accounts`
WHERE `profileid` = '100'))
AND `id` NOT IN (SELECT `postid`
FROM `user_posts_removed`
WHERE `profileid` = '100')
AND `live` = '1'
AND `added` >= Date_sub(Now(), INTERVAL 1 month)
AND `popularity` > 1
ORDER BY `popularity` DESC
LIMIT 50
Thank you.
Edit:
I am using MySQL version 5.7.24, so unfortunately the row_number() function will not work in this instance.

Answer 1

In MySQL 8+, you would simply use row_number():
select sp.*
from (select sp.*,
row_number() over (partition by posted_by order by popularity desc) as seqnum
from source_posts sp
) sp
where seqnum <= 5
order by popularity desc
limit 50;
I'm not sure what the rest of your query is doing, because it is not described in your question. You can, of course, add additional filtering criteria or joins.
EDIT:
In earlier versions, you can use variables:
select sp.*
from (select sp.*,
(#rn := if(#p = posted_by, #rn + 1,
if(#p := posted_by, 1, 1)
)
) as rn
from (select sp.*
from source_posts sp
order by posted_by, popularity desc
) sp cross join
(select #p := '', #rn := 0) params
) sp
where rn <= 5
order by popularity desc
limit 50;

Answer 2

Could try the row number function. Using that, it would assign each employee a distinct "id." So if one employee had 50 records, only those with a row_number (named as "rank") less than or equal to 5 would be returned.
Select *
from(
SELECT `source_posts.*`, row_number() over (partition by `username` order by `popularity` desc) as rank
FROM `source_posts`
WHERE `posted_by` IN (SELECT `username`
FROM `source_accounts`
WHERE `id` IN (SELECT `sourceid`
FROM `user_source_accounts`
WHERE `profileid` = '100'))
AND `id` NOT IN (SELECT `postid`
FROM `user_posts_removed`
WHERE `profileid` = '100')
AND `live` = '1'
AND `added` >= Date_sub(Now(), INTERVAL 1 month)
AND `popularity` > 1
ORDER BY `popularity` DESC
LIMIT 50 `enter code here`)
where rank <= 5