select a.uid,b.exam_id,round(avg(b.score),0) as avg_score
from user_info a,exam_record b,examination_info c 
where a.uid=b.uid and b.exam_id=c.exam_id
and substr(c.tag,1,1) in('c','C')
and b.score>0 
and (a.nick_name rlike '^牛客[0-9]+号$' or a.nick_name rlike '^[0-9]+$')

group by 1,2 order by 1,3