分组计算时要包含前一组的最后一条记录，怎么实现？

注意：这是mysql版本的写法，仅供参考；并且写的SQL比较复杂，性能应该比较差，可以自行进行下优化；

select date_format(time,'%Y-%m-%d')as time, sum(vol) from 
(
    -- 数据拼接：拼接分组后每组中最小时间和上一组的最大时间的vol值
    select i.time,  j.vol  from
    (
			 select time, max(time1)as time1 from
				(
						select e.time as time, f.time as time1 from test e,
						(
								-- 获取分组后的除最后一组之外的每组中最后一条数据
							 select c.time, d.vol from
								(
									 select a.time from
									 (select max(time) as time  from test group by date_format(time,'%Y-%m-%d') order by time) a ,
									 (select max(time) as time  from test group by date_format(time,'%Y-%m-%d') order by time desc  limit 1) b 
									 where a.time != b.time 
								)c, test d 
								where c.time = d.time
						) f
						where e.time > f.time  group by date_format(e.time,'%Y-%m-%d') ,date_format(f.time,'%Y-%m-%d') 
						
				) h group by time
    )i, test j where i.time1 = j.time

		union all

		-- 查询分组后每组的最大时间和每组求和后的vol值
		select max(time) as time, sum(vol) as vol  from test group by date_format(time,'%Y-%m-%d') order by time 
) g group by date_format(g.time,'%Y-%m-%d')