oracle 上下行某字段相減

select a.active_time,b.active_time,(a.active_time - b.active_time),a.num,b.num from (select row_number() over (order by t.create_time desc) num,t.* from YB_WC_MONITOR t) a, (select row_number() over (order by t1.create_time desc) num,t1.* from YB_WC_MONITOR t1) b where a.num=b.num-1;