1661.每台机器的进程

表: Activity

方法1：窗口函数

select machine_id,round(avg(sumtime),3)as processing_time
from 
(select *,end_timestamp-timestamp as sumtime
   from
   (select *,
        lead(timestamp,1) over (partition by machine_id,process_id
        order by activity_type asc) as end_timestamp
    from activity) as a
where end_timestamp is not null) as b 
group by machine_id; 

方法2：表连接