mysql使用GROUP BY分组实现取前N条记录的方法

SELECT a.id,a.SName,a.ClsNo,a.Score FROM aa a LEFT JOIN aa b ON a.ClsNo=b.ClsNo AND a.Score<b.Score group by a.id,a.SName,a.ClsNo,a.Score having count(b.id)<2 ORDER BY a.ClsNo,a.Score descSELECT a.id,a.SName,a.ClsNo,a.Score FROM aa a LEFT