select CLASSNO  COURSE, count(*) as '人数' from (

select * from 表 a left join (

select   COURSE as 'COURSE_'  ,AVG(GRADE) as 'AVG_GRADE' from  表 group by COURSE )  b  on  a.COURSE = b.COURSE_  )  c 

 where GRADE < AVG_GRADE  group by CLASSNO ,COURSE 

比较蠢，但是应该能满足你说的，截图不全 默认你整个表都是一个年级。如果不是自己再调整SQL

弄个子查询，然后当判断条件就好了

类似这样

select * from a

where grade < (select avg(grade) fom a)

SELECT classno,course,COUNT(*) FROM aaa WHERE grade < (SELECT AVG(grade) FROM aaa) GROUP BY course,classno;