题解 | #0级用户高难度试卷的平均用时和平均得分#

select uid,
round(avg(if(score is not null,score,0)),0) as avg_score,
round(avg(if(submit_time is not null,timestampdiff(minute,start_time,submit_time),duration)),1) as avg_time_took
from exam_record left join user_info using(uid)
left join examination_info using(exam_id)
where level=0 and difficulty='hard'
group by uid