SQL Question - Need a query
I have a SQL question (Using Oracle Release 9.2)
In our application we have item_cost_history table which stores cost of an item on a particular date.
Item_Cost_History: Item_Id, Item_Cost, Cost_Date.
Item_Cost is downloaded everyday and we maintain an archive of item_cost by cost_date so as to fetch the cost as of a particular date.
The query (Q1) used to get cost is
where item_id = given_item_id
and cost_date = given_date;
This query is present throughout the code.
Since the cost of an item does not change very frequntly, we are storing the same repeated cost over and over again with different dates. As a result the table size is huge because we keep atleast 30 day archive for 500,000 items.
To reduce the amount of data we are storing, we have decided to change our approach in storing item_cost and record changes to item_cost only We are going to create a new table Item_Cost_Archive and record only cost changes and create a view Item_Cost_History so that the schema change is transparent to the application.
Item_Cost_Archive : Item_Id, Item_Cost, Last_Cost_Modify_Date.
Item1 3.00 17-JAN-2004
Item1 3.20 31-JAN-2004
Item1 3.15 17-FEB-2004
Is there a way to create a view (Item_Cost_History) so that Q1 can be executed as it is and fetch results.
2 Solutions but still you need to edit the query
1] Solution without View, direct on the new table
from Item_Cost_History_New a
where item_id = &given_item_id
and Last_Cost_Modify_Date =(select max(Last_Cost_Modify_Date)
from Item_Cost_History_New b
where Last_Cost_Modify_Date <= &given_date
and a.item_id = b.item_id);
2] Solution with View and Minor change to your query
View Definition :
Select a.item_id, a.item_cost, a.Last_Cost_Modify_Date as "startDate" ,min(b.Last_Cost_Modify_Date) AS "EndDate"
from Item_Cost_History_New a, Item_Cost_History_New b
where a.Last_cost_modify_date < b.last_cost_modify_date
and a.item_id = b.item_id
group by a.item_id,a.item_cost, a.Last_Cost_Modify_Date
select a.item_id, a.item_cost, a.last_cost_modify_date as "StartDate", to_date('31-Dec-2100') as "MaxDate"
from Item_cost_History_New a, (Select item_id, max(Last_Cost_Modify_Date) as Max_Last_Cost_Modify_Date
From Item_Cost_History_New b
Group by Item_id) b
where a.item_id = b.Item_id
and a.Last_Cost_Modify_Date = b.Max_Last_Cost_Modify_Date
If the table is :
ITEM_ID ITEM_COST LAST_COST_M
--------------- --------------- -----------
10 100 01-JAN-2001
10 102 10-FEB-2002
10 103 10-MAR-2002
20 201 10-JAN-2010
20 202 30-JAN-2011
30 401 01-FEB-2004
Then The view will be
ITEM_ID ITEM_COST startDate EndDate
--------------- --------------- ----------- -----------
10 100 01-JAN-2001 10-FEB-2002
10 102 10-FEB-2002 10-MAR-2002
10 103 10-MAR-2002 31-DEC-2100
20 201 10-JAN-2010 30-JAN-2011
20 202 30-JAN-2011 31-DEC-2100
30 401 01-FEB-2004 31-DEC-2100
The query to find the item Cost:
where item_id = given_item_id
and startDate <= given_date
and EndDate > given_date;
-- As far as my knowledge goes Oracle offers a way to create a View which will return different records according to session environment variables (or context value). Combining that feature with the above view definition you can get the exact answer to your problem. If you get how to do it then please paste the result in the forum and also mail me.