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
http://www.nowcoder.com/practice/e9e7dc4c8623467793f6999cbfee9360
两表连接，再聚合计算平均值
select course_name, round(avg(timestampdiff(minute, in_datetime,out_datetime)),2) avg_Len
from
course_tb
join
attend_tb
using (course_id)
group by course_name
order by avg_Len desc
投递正浩创新EcoFlow等公司10个岗位