题解 | #试卷发布当天作答人数和平均分#

select er.exam_id,
       count(distinct ui.uid) as uv,
       round(sum(score) / count(submit_time),1) as avg_score
from exam_record er
join user_info ui using(uid)
where ui.level>5 and
      exam_id in 
	  #筛选出当天有作答记录的试卷id
	  (select exam_id
                  from exam_record 
                  join examination_info using(exam_id)
                  where DATE_FORMAT(submit_time,'%Y%m%d') = DATE_FORMAT(release_time,'%Y%m%d') and tag="SQL")
group by er.exam_id
order by uv DESC,avg_score

不明白为什么这样可以通过,如果现在有一个人A,A是五级以上,但是A并没有在试卷发布当天做该试卷,而有B在试卷发布当天做了,那么这套试卷的id就会被查询出来,后续只需要在筛选做这个试卷的人的等级就可以了,那么A不是被误算进来了嘛?