LEFT JOIN order and limit
LEFT JOIN ps a ON a.account_id = fr.author
LEFT JOIN ps a ON a.PrimaryKey --- the Primary Key of ps = ( SELECT b.PrimaryKey FROM ps AS b WHERE b.account_id = fr.author ORDER BY b.level DESC LIMIT 1 )
Replace the LEFT JOIN clause with something like:
... LEFT JOIN (SELECT b.account_id, b.name FROM (SELECT c.account_id, MAX(c.level) AS level FROM ps AS c GROUP BY c.account_id) AS d JOIN ps AS b ON b.account_id = d.account_id AND b.level = d.level ) AS a ON (a.account_id = fr.author) ...
This will still return multiple rows if there were several rows in
ps with the same account ID and the same level and that level was the maximum level:
NAME | LEVEL Test1 | 1 Test2 | 120 Test3 | 2 Test4 | 1 Test5 | 120
If this situation can arise, then you have to decide what you want to do - and tune the query appropriately. For example, you might decide to use
MAX(b.name) with a GROUP BY clause to arbitrarily select the alphabetically later of the two names.