题解 | #牛客直播各科目平均观看时长#
牛客直播各科目平均观看时长
https://www.nowcoder.com/practice/e9e7dc4c8623467793f6999cbfee9360
select course_name, round(AVG(duration), 2) as avg_Len
from (
select b.course_name, a.course_id, TIMESTAMPDIFF(MINUTE, a.in_datetime, a.out_datetime) as duration
from attend_tb as a
left join course_tb as b
on a.course_id = b.course_id
) as c
group by course_name
order by avg_Len desc;
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