select min(字段) from table group by 分组
select *
from table
where (LINE_ID, timediff) in
(select LINE_ID, min(timediff) from table group by LINE_ID);
select LINE_ID,ORDER_NO,BR_NO,min(timediff) from table group by LINE_ID,ORDER_NO,BR_NO
不知道你这个问题是否已经解决, 如果还没有解决的话: