SELECT g.id,l.name,g.score
  FROM 
(SELECT id,language_id,score,
        DENSE_RANK() OVER(PARTITION BY language_id ORDER BY score DESC) AS rk
   FROM grade) g
  LEFT JOIN language l ON l.id = g.language_id
 WHERE g.rk <= 2
 ORDER BY l.name,g.score DESC,g.id

开个窗口函数 DENSE_RANK 1,1,1,2 排名