Lifo SQL Query

Hai,

I want to generate the simple LIFO based SQL query for my Purchase table:

      The sample data would be in Purchase table like that:

      Order No.   Date                 Item Code         Quantity       Purchase Price
      1               02-Aug-2012          A                          97000        14.50
      2               03-Aug-2012          B                          12800        99.80
      3               04-Aug-2012          B                          27500        95.80
      4               05-Aug-2012          A                          45000        14.60
      5               05-Aug-2012          A                          55000        13.80
      6               06-Aug-2012          B                          45000        97.00
      7               07-Aug-2012          A                          11400        10.50
      8               08-Aug-2012          B                          11600        95.60
      9               09-Aug-2012          A                          12000        12.60


I want to get the purchase cost of 60000 Lots of Item A using LIFO based method, it means that lastest purchases on the basis of date will be calculated for cost so the aspected result will be:
      
      Purchase cost of 60000 lots of item A will be 799980/-

            Following is the record wise breakup of getting result of 799980/-
            09-Aug-2012      105      12000          14.60      
            07-Aug-2012      105      11400          10.50
            05-Aug-2012      105      36600          13.80


Following is the SQL script for generating Purchase table and Inserting data in it:

      create table purchase (order_number number(5), order_date date,
        item_code varchar2(10), Quantity number(10), Price number(8,2));

      insert into purchase values  ('1','02-Aug-2012','A',97000,14.50);
      insert into purchase values  ('2','03-Aug-2012','B',12800,99.80);
      insert into purchase values ('3','04-Aug-2012','B',27500,95.80);
      insert into purchase values ('4','05-Aug-2012','A',45000,14.60);
      insert into purchase values ('5','05-Aug-2012','A',55000,13.80);
      insert into purchase values ('6','06-Aug-2012','B',45000,97.00);
      insert into purchase values ('7','07-Aug-2012','A',11400,10.50);
      insert into purchase values ('8','08-Aug-2012','B',11600,95.60);
      insert into purchase values ('9','09-Aug-2012','A',12000,12.60);

Looking forward for prompt and positive feedback in this regard.

Thank you...