select max(t2.a) amax,t2.b from (
select t.a,t.b from 
t,(select b,max(a) amax from t where b=2 group by b) t1
where t.b=1 and t.a>t1.amax) t2
group by t2.b;

------解决方案--------------------
SQL code

with t1 as
(
     select 1 c1,2 c2 from dual
     union all
     select 3 c1,1 c2 from dual
     union all
     select 4 c1,2 c2 from dual
     union all
     select 6 c1,1 c2 from dual
)

select min(c1) c1
from t1
where c2 = 1 and c1 > (select max(c1) from t1 where c2 = 2)


     c1
------------------
1    6