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1. join ① inner join：两张表进行连接查询时，只保留两张表中完全匹配的结果集 ② left join：在两张表进行连接查询时，只返回左表所有行，而右表中没有匹配的记录则会NULL ③ right join：只返回右表所有行，而左表中没有匹配的记录则会NULL ④ full join：返回坐标和右表中所有没有匹配的行 2. 集中排序窗口函数的区别 ① row_number()：相同值排名不同，序号连...

select date(in_time) as dt, round(sum(timestampdiff(second,in_time, out_time))/count(distinct uid),1) as avg_viiew_len_sec from tb_user_log where date_format(in_time, "%Y-%m") = "2021-11" and artical_id!=0 group by dt order by avg

题目来源：牛客网sql大厂面试真题 01某音短视频 问题1 select t1.video_id, round(sum(if(t1.end_time-t1.start_time >= t2.duration, 1,0))/count(t1.start_time),3) as avg_comp_play_rate from (select * from tb_user_video_log where year(start_time) = 2021)t1 le.