求班级最大、最小、平均分，以及查过平局分人数

select z.*,m.sl from

(SELECT classno,max(grade),min(grade),avg(grade) FROM STSCORE group by classno) z

left join 

(select classno,count(*) as sl from 

(select a.*,b.pj from STSCORE a left join 

(SELECT classno,avg(grade) as pj  FROM STSCORE  group by classno) b on a.classno=b.classno) where grade>pj group by classno) m on z.classno=m.classno

和你上一个问题没区别啊 一个是按性别来，一个按科目来~