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(TIMESTAMPDIFF(MINUTE, in_datetime, out_datetime)), 2 ) AS avg_len FROM attend_tb JOIN course_tb USING(course_id) GROUP BY course_name ORDER BY avg_len DESC