UPDATE 表A 
set z=b.id 
from (select a.* from x as a where a.time in (select max(time)from x where type =x.type)) b
where a.type = b.type

------解决方案--------------------
SQL code
create table x(id int,type int,time datetime,filepath int)
create table a(z int,type int,time datetime,filepath int)
insert x
select 1, 1, '2011-01-01 14:00:00',1 union all
select 2, 1, '2011-01-01 17:00:00',2 union all
select 3, 1, '2011-01-01 12:00:00',3
insert a
select 0,1,null,null
go
update a set a.z=b.id,a.time=b.time,a.filepath=b.filepath  from a
join x b on a.type=b.type
where b.time=(select max(time) from x where a.type=type)
go
select * from a
go
drop table x,a