create table test1 ( part number, code number, quantity number, attr1 varchar2(100), attr2 varchar2(100), attr3 varchar2(100) );

insert into test1 values ( 1,  1, 3, 'a', 'a', 'a');
insert into test1 values ( 1,  2, 4, 'a', 'b', 'b');
insert into test1 values ( 1,  3, 5, 'b', 'b', 'c');
insert into test1 values ( 1,  4, 100, null, null, null);
insert into test1 values ( 2,  5, 0, 'a', 'b', 'c');
insert into test1 values ( 2,  6, 1, 'a', 'a', 'b');
insert into test1 values ( 2,  7, 2, 'b', 'b', 'a');
insert into test1 values ( 2,  8, null, 'a', 'b', 'c');
commit;

select part,
       max((select inn.attr
           from (select row_number() over(order by decode(test1.attr1, null, 0, 1) desc, sum(test1.quantity) desc) rn,
                        test1.attr1 attr
                 from test1
                 where test1.part = t.part
                 group by test1.attr1) inn
           where inn.rn = 1)) attr1,
       max((select inn.attr
           from (select row_number() over(order by decode(test1.attr2, null, 0, 1) desc, sum(test1.quantity) desc) rn,
                        test1.attr2 attr
                 from test1
                 where test1.part = t.part
                 group by test1.attr2) inn
           where inn.rn = 1)) attr2,
       max((select inn.attr
           from (select row_number() over(order by decode(test1.attr3, null, 0, 1) desc, sum(test1.quantity) desc) rn,
                        test1.attr3 attr
                 from test1
                 where test1.part = t.part
                 group by test1.attr3) inn
           where inn.rn = 1)) attr3
from test1 t
group by part ;

with inn as
 (select code,
         part,
         attr1,
         nvl2 ( attr1 , sum(test1.quantity) over(partition by part, attr1) , -1) q1,
         attr2,
         nvl2 ( attr1 , sum(test1.quantity) over(partition by part, attr2) , -1) q2,
         attr3,
         nvl2 ( attr1 , sum(test1.quantity) over(partition by part, attr3) , -1) q3
  from test1)
select part, max(attr1) keep ( dense_rank first order by q1 desc ) attr1,
max(attr2) keep ( dense_rank first order by q2 desc ) attr2,
max(attr3) keep ( dense_rank first order by q3 desc ) attr3
from inn
group by part;