Incorporando um valor de incremento neste sql

select id, perCent, 
       @curRank := if(parent = @prevParent, @curRank + 1, 1) AS rank,
       @prevParent := parent
from (
    select child.id, child.perCent, child.parent
    from likesd parent
    join likesd child
       on parent.id = child.parent
    where parent.type = 3
    order by parent.id, child.perCent desc) x
cross join (SELECT @curRank := 0, @prevParent := null) r