查询Student表中男女同学分别小于60的成绩最高的学号(一个结果集)
*如有相同成绩则优先取学号靠前的
select a.sex,max(a.no),max(b.score) from student a join (select sex,max(score) score from student where score<60 group by sex) b on a.sex=b.sex where a.score=b.score group by a.sex