create table ss_main(车号 varchar(10),行驶日期 datetime,序号 int)
insert into ss_main select '1234','2011-12-14',1
insert into ss_main select '1234','2011-12-14',3
insert into ss_main select '1234','2011-12-15',1
insert into ss_main select '1234','2011-12-15',2
insert into ss_main select '1234','2011-12-15',3
insert into ss_main select '1235','2011-12-16',7
insert into ss_main select '1235','2011-12-16',8
insert into ss_main select '1235','2011-12-15',15
go
select * from SS_Main a 
where not exists(select 1 from ss_main where 车号=a.车号 and (行驶日期>a.行驶日期 or 行驶日期=a.行驶日期 and 序号>a.序号))
/*
车号         行驶日期                    序号
---------- ----------------------- -----------
1234       2011-12-15 00:00:00.000 3
1235       2011-12-16 00:00:00.000 8

(2 行受影响)

*/
go

------解决方案--------------------
SQL code
--2005+
select
 distinct b.*
from
  tb a
cross apply
  (select top 1 * from tb where  车号=a.车号 order by 行驶日期 desc)b

--TB是指你查出的结果集

------解决方案--------------------
SQL code
SELECT 
调度单号,车号,行驶日期 ,序号 ,行驶线路
FROM (Select 调度单号,车号,行驶日期 ,序号 ,行驶线路,ROW_NUMBER()OVER(PARTITION BY 车号 ORDER BY 行驶日期 DESC) AS row1,ROW_NUMBER()OVER(PARTITION BY 车号 ORDER 

BY 行驶日期 DESC) AS row2 from 表SS_Main
)t
WHERE row1=1