题解 | #0级用户高难度试卷的平均用时和平均得分#

这道题也简单的，贴个代码

主要的坑：就是如果用户没做完试卷【即submit_time为null】，就要用这个试卷的duration代替

select 
    re.uid,
    round(avg(IFNULL(re.score,0)),0) 	avg_score,
    round(avg(ifnull(timestampdiff(minute, start_time, submit_time), info.duration)),1)  	avg_time_took
from 
    exam_record re
left join
    user_info uinfo
using(uid)
left join
    examination_info info
using(exam_id)
where uinfo.level = 0 and 
    difficulty = 'hard'
GROUP BY  uid