Mysql 相邻两行记录某列的差值方法

select r1.company_id, r1.touch_time, r2.touch_time, r1.touch_time - r2.touch_time from (select (@rownum := @rownum + 1) as rownum,  info.company_id,  info.touch_time  from sys_touch_info info, (select @rownum := 0) r  where info.touch_time is not null  order by info.company_id) r1 left join (select (@index := @index + 1) as rownum,   info.company_id,   info.touch_time  from sys_touch_info info, (select @index := 0) r  where info.touch_time is not null  order by info.company_id) r2 on r1.company_id = r2.company_id and r1.rownum = r2.rownum - 1