with t1 as
(
     select 1 id,'xh001' xh,'张三' name from dual
     union all
     select 2 id,'xh002' xh,'李四' name from dual
),
t2 as
(
     select 1 id,'xh001' xh,date'2012-09-21' time,'192.168.100.100' ip from dual
     union all
     select 2 id,'xh001' xh,date'2012-09-23' time,'192.168.100.101' ip from dual
     union all
     select 3 id,'xh001' xh,date'2012-09-28' time,'192.168.100.102' ip from dual
     union all
     select 4 id,'xh002' xh,date'2012-09-22' time,'192.168.100.103' ip from dual
     union all
     select 5 id,'xh002' xh,date'2012-09-28' time,'192.168.100.104' ip from dual
     union all
     select 6 id,'xh002' xh,date'2012-09-24' time,'192.168.100.105' ip from dual
)

select c.xh,c.name,d.time,d.ip
from t1 c,
     (
      select a.*
      from t2 a,(select xh,max(time) time from t2 group by xh) b
      where a.xh = b.xh and a.time = b.time
      ) d
where c.xh = d.xh


     xh    name    time            ip
---------------------------
1    xh001    张三    2012/9/28    192.168.100.102
2    xh002    李四    2012/9/28    192.168.100.104