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