题解 | #试卷发布当天作答人数和平均分#

select
    er.exam_id,
    count(distinct er.uid) as uv,
    round(avg(score),1) as avg_score
from 
    exam_record er
inner join
    examination_info ei on er.exam_id = ei.exam_id
inner join
    user_info ui on er.uid = ui.uid
where 
    ui.level > 5 and ei.tag = 'SQL' 
    and date_format(ei.release_time,'%Y%m') = date_format(er.start_time,'%Y%m')
group by 
    1
order by 
    2 desc,3