create table tbjob
(id int, userid varchar(5), jontime datetime)

insert into tbjob
select 1, '0001', '2012-1-1 00:12:02' union all
select 2, '0001', '2012-1-1 10:12:12' union all
select 3, '0002', '2012-1-1 11:12:12' union all
select 4, '0002', '2012-1-2 12:12:12' union all
select 5, '0003', '2012-3-4 01:12:12'


with t as
(select row_number() over(partition by userid order by jontime desc) rn,
   id,userid,jontime from tbjob
)
select id,userid,jontime
from t
where rn=1
order by jontime desc

id          userid jontime
----------- ------ -----------------------
5           0003   2012-03-04 01:12:12.000
4           0002   2012-01-02 12:12:12.000
2           0001   2012-01-01 10:12:12.000

(3 row(s) affected)