Sql156 average completion rate of each video

/*
 Calculation 2021 In the year 、 Every video with playback record 、 The completion rate of broadcasting ( The result is three decimal places ), And sort them in descending order according to the completion rate 

 Ideas ： Find the smallest unit of processing , Write code from bottom to top , Add restrictions 
1、 Disassemble attributive , Find the core decoration ： Completion rate 
2、 Completion rate = Number of finished broadcasts / Total playback times 
——> Number of finished broadcasts ： End viewing time - Start playback time >= Number of users with video duration , Deemed as finished broadcasting 
            end_time-start_time>=duration
            ** The end of the broadcast is recorded as 1, The unfinished broadcast is 0, all 1 The sum is the completion times 
            sum(if(end_time-start_time>=duration,1,0))
——> Total playback times ： appear start_time For one play 
            count(start_time)

 Knowledge point ：if function ,sum function , Left connection ,round function ,year function 
1、left join on+ Conditions 
2、round(a,3) Keep three decimal places 
*/


select a.video_id,round(sum(if(end_time-start_time>=duration,1,0))
                        /count(start_time),3) avg_comp_play_rate
from tb_user_video_log a
left join tb_video_info b
on a.video_id=b.video_id
where year(start_time)=2021
group by a.video_id
order by avg_comp_play_rate desc