select t1.group_id, t2.val
from (select t1.group_id,
             max(t1.t2_id1) keep (dense_rank first order by t1.group_id) as t2_id1,
             max(t1.t2_id2) keep (dense_rank first order by t1.group_id) as t2_id2
      from t1
      group by t1.group_id) t1,
     
       t2
where t1.t2_id1 = t2.id1
   and t1.t2_id2 = t2.id2