SELECT
    a.id_concessionaria,
    a.avscore,
    @rank := @rank + 1 AS ranking
FROM
    (
        SELECT
            id_concessionaria,
            Avg(rating) AS AvScore
        FROM
            dealer_ratings
        GROUP BY
            id_concessionaria
    ) a
ORDER BY
    a.avscore DESC

12286   5.0000  1
11393   5.0000  2
11784   5.0000  3
11816   5.0000  4
12291   4.3333  5 --------------------- Essa aqui
12634   4.0000  6
19021   3.0000  7
10194   2.0000  8