题解 | #试卷发布当天作答人数和平均分#

select c.exam_id,
count(distinct c.uid) uv,
round(sum(score)/count(score),1) avg_score
from 
user_info a,examination_info b,exam_record c
where
a.uid=c.uid
and
b.exam_id=c.exam_id
and
c.uid in(
    select uid from user_info
    where level>5
)
and
date(c.start_time)=date(b.release_time)
group by exam_id
order by uv desc,avg_score asc