Select the newest value of a row in a group by

Question

On the following query I would like to select the value of the column new_cost which belongs to the row with the newest date in the column m.creation_date, instead of using max(new_cost)
select s.segment1, segment2, m.organization_id, sum(primary_quantity), max(new_cost)
from inv.mtl_material_transactions m, inv.mtl_system_items_b s
where s.segment2 = 1000435
and m.organization_id = 83
and s.organization_id = 136
and m.inventory_item_id = s.inventory_item_id
group by s.segment1, s.segment2, m.organization_id
order by s.segment1, s.segment2, m.organization_id for example, on the following table I would like to choose the new_cost of the row with the creation date 20/08/2010 14:37 (row 4)
SEGMENT1     SEGMENT2     ORGANIZATION_ID     PRIMARY_QUANTITY     NEW_COST     CREATION_DATE
1     1000435     83     0,66668     175.500     04/06/2010 16:41
1     1000435     83     1     189.106     22/06/2010 11:54
1     1000435 83     -0,58333     189.106     19/07/2010 11:55
1     1000435     83     1     198.459     20/08/2010 14:37
1     1000435     83     -0,5     189.106     11/08/2010 18:12

Answer 1

You should be able to use an analytic function... something similar to:
with data
as
     select 1 segment1, 1000435 segment2, 83 organization_id, 0.66668 primary_quantity, 175.500 new_cost, to_date('04/06/2010 16:41', 'DD/MM/YYYY HH24:MI:SS') creation_date
     from dual
     union all
     select 1 segment1, 1000435 segment2, 83 organization_id, 1 primary_quantity, 189.106 new_cost, to_date('22/06/2010 11:54', 'DD/MM/YYYY HH24:MI:SS') creation_date
     from dual
     union all
     select 1 segment1, 1000435 segment2, 83 organization_id, -0.58333 primary_quantity, 189.106 new_cost, to_date('19/07/2010 11:55', 'DD/MM/YYYY HH24:MI:SS') creation_date
     from dual
     union all
     select 1 segment1, 1000435 segment2, 83 organization_id, 1 primary_quantity, 198.459 new_cost, to_date('20/08/2010 14:37', 'DD/MM/YYYY HH24:MI:SS') creation_date
     from dual
     union all
     select 2 segment1, 1000435 segment2, 83 organization_id, -0.5 primary_quantity, 189.106 new_cost, to_date('11/08/2010 18:12', 'DD/MM/YYYY HH24:MI:SS') creation_date
     from dual
select segment1, segment2, organization_id, primary_quantity_sum, new_cost
from (
    select
          segment1,
          segment2,
          organization_id,
          sum(primary_quantity) over (
               partition by
                    segment1,
                    segment2,
                    organization_id
          ) primary_quantity_sum,
          new_cost,
          row_number() over (
               partition by
                    segment1,
                    segment2,
                    organization_id
               order by
                    creation_date desc
          ) rn
    from data
    where segment2 = 1000435
where rn = 1