select b.course_id,course_name,round(count(distinct case when timestampdiff(minute,in_datetime,out_datetime)>=10 then a.user_id else null end)*100/count(distinct case when if_sign=1 then b.user_id else null end),2) as 'attend_rate(%)' from attend_tb a left join behavior_tb b on a.user_id=b.user_id and a.course_id=b.course_id left join course_tb c on b.course_id=c.course_id group by b.course_id,course_name order by b.course_id 我这个为什么不对呢？嘤嘤嘤