GROUP_CONCAT with limit

Question

I have table with player-s in many-to-many relation with skill-s

The goal is to list the players and their \"top 3 skills\" with a single q

Answer 1

You can simulate the partitioned row_number using user variables and then limit rows and apply group_concat:

select p.id,
    group_concat(s.title separator ', ') as skills
from player p
left join (
    select distinct ps.player_id,
        ps.skill_id,
        @rn := if(@player_id = player_id, @rn+1, if(@player_id := player_id, 1, 1)) as seqnum
    from player_skills ps
    cross join (select @rn := 0, @player_id := null) x
    where ps.value > 2
    order by player_id, value desc
    ) ps on p.id = ps.player_id and ps.seqnum <= 3
left join skill s on ps.skill_id = s.id
group by p.id;

Demo

This method doesn't require any table to read more than once.