select er.exam_id,
count(distinct er.uid) as uv,

round(avg(score),1) avg_score

from examination_info ei
join exam_record er on ei.exam_id = er.exam_id
join user_info ui on er.uid = ui.uid 

where tag='SQL'
and level >5
and date_format(start_time,'%Y%m%d')=date_format(release_time,'%Y%m%d')


group by er.exam_id
order by uv desc,avg_score