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
with a as(select course_id, round(avg(timestampdiff(minute,in_datetime,out_datetime)),2) avg_Len from attend_tb group by 1 order by 2 desc) select b.course_name, a.avg_Len from a left join course_tb b on a.course_id=b.course_id
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