需要显示各班级各科低于年级平均分的人数

需要显示各班级各科低于年级平均分的人数
我的不对
SELECT
CLASSNO,
COURSE,
COUNT ( SELECT GRADE FROM STSCORE WHERE GRADE < ( SELECT AVG( GRADE ) FROM STSCORE GROUP BY COURSE, CLASSNO ) )
FROM
STSCORE

select classno,course,avgg,count(*) num
from (
select a.classno,a.course,a.grade,a.studentno,t1.avgg 
from STSCORE a JOIN
(select avg(grade) avgg,classno,course from stsco GROUP BY classno,course) t1 
ON a.classno = t1.classno and a.course=t1.course
) t2
GROUP BY classno,course
HAVING grade<avgg

select
    classno,
    course,
    avgg,
    count( studentno ) as shuliang 
from
    (
    select
        a.classno,
        a.course,
        a.gradee,
        a.studentno,
        p.avgg 
    from
        stscore a
        join ( select avg( gradee ) as avgg, classno, course from stscore b group by course, classno ) p on a.classno = p.classno 
        and a.course = p.course 
    ) m 
group by
    course,
    gradee 
having
    gradee < avgg