Help with query to determine if a record value has changed.

Question

Our auditors want to know which items had their costs updated in March 2006. I'm querying the cst_standard_cost table to find records that were updated in March. This part seems to be working although it pulls back multiple rows for the same item if more than one update was done in that month. I'm still not sure how I'm going to handle that problem.
----cst_standard_costs-----
alter session set NLS_DATE_FORMAT = 'MM/DD/YYYY';
drop table suss.cost_update_0306b;
create table suss.cost_update_0306b
as
select csc.inventory_item_id, mtl.segment1||','||mtl.segment2 "item", csc.organization_id,csc.standard_cost,csc.creation_date "creation_date"
from cst_standard_costs csc, mtl_system_items_b mtl
where csc.inventory_item_id = mtl.inventory_item_id
and mtl.organization_id = '82'
and csc.organization_id not in ('0','81')
and csc.creation_date like '03/%/2006%'
order by csc.inventory_item_idHere, I'm trying to find if the update that was done in March actually changed the item's cost. But the sql is not exactly right. The results being returned are any cost update where the item's cost is different than it was in March. I'd like to pull back the item's cost from the most recent cost update previous to the March update and see if it differs from the March cost.
select csc.inventory_item_id,mtl.segment1||','||mtl.segment2, csc.organization_id,csc.standard_cost, csc.creation_date
from cst_standard_costs csc, mtl_system_items_b mtl, suss.cost_update_0306b scu
where csc.inventory_item_id = mtl.inventory_item_id
and mtl.organization_id = '82'
and scu.inventory_item_id = csc.inventory_item_id
and csc.organization_id not in ('0','81')
and csc.creation_date < scu."creation_date"
and csc.standard_cost <>scu.standard_cost
order by csc.inventory_item_id ascHere's a simple example
item id.....cost.........update_date
24..........45.00........03/01/2006
24..........45.00........02/01/2006
24..........30.00........02/22/2006
40..........45.00........03/01/2006
40..........30.00........02/01/2006
40..........28.00........02/22/2006
The results of the sql should be to return item id 40 because the costs changed in March but not item id 24 because the costs did not change in March

Answer 1

Something like this:
SQL> DESC COSTS;
Name                                      Null?    Type
ITEM_ID                                            NUMBER
COST                                               NUMBER(4,2)
UPDATE_DATE                                        DATE
SQL> SELECT * FROM COSTS;
   ITEM_ID       COST UPDATE_DAT
        24         40 03/01/2006
        24         45 02/01/2006
        40         45 03/01/2006
        40         30 02/01/2006
SQL> SELECT b.item_id, b.cost, b.update_date
  2  FROM costs a, costs b
  3  WHERE a.item_id = b.item_id
  4   AND a.cost <> b.cost
  5   AND a.update_date = ADD_MONTHS(b.update_date, -1)
  6  /
   ITEM_ID       COST UPDATE_DAT
        24         40 03/01/2006
        40         45 03/01/2006It is maybe not efficient query but works :)
Another solution:
  1  SELECT a.item_id, a.cost, a.update_date
  2  FROM costs a
  3  WHERE a.cost <> (SELECT cost
  4               FROM costs
  5               WHERE a.item_id = item_id
  6                AND ADD_MONTHS(a.update_date, -1) = update_date
  7*            )
SQL> /
   ITEM_ID       COST UPDATE_DAT
        24         40 03/01/2006
        40         45 03/01/2006Peter D.