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(score),0) as avg_score,
       round(avg(time_took),1) as  avg_time_took
from (
    select t1.uid,
           coalesce(timestampdiff(minute,start_time,submit_time),duration) as time_took,
           coalesce(score,0) as score
    from user_info t1
    join exam_record t2 on t1.uid = t2.uid
    join examination_info t3 on t2.exam_id = t3.exam_id
    where level = 0 and difficulty = 'hard'
    ) t
group by uid