Calculate Profit Based on First-In, First-Out Pricing

Question

Say I have purchase and sales data for some SKUs:

po_id | sku | purchase_date    | price | qty
----------------------------------------------
    1 | 123 | 2013-         


        

Answer 1

Good question. The approach that I'm taking is to calculate the total sales. Then calculate cumulative purchases, and combine them with special logic to get the right arithmetic for the combination:

select s.sku,
       (MarginPos - SUM(case when s.totalqty < p.cumeqty - p.qty then p.price * p.qty
                             when s.totalqty between p.cumeqty - p.qty and p.qty
                             then s.price * (s.totalqty - (p.cumeqty - p.qty))
                             else 0
                        end)
       ) as Margin
from (select s.sku, SUM(price*qty) as MarginPos, SUM(qty) as totalqty
      from sales s
     ) s left outer join
     (select p.*,
             (select SUM(p.qty) from purchase p2 where p2.sku = p.sku and p2.sale_id <= p.sale_id
             ) as cumeqty
      from purchase s
     )
     on s.sku = p.sku
group by s.sku, MarginPos

Note: I haven't tested this query so it might have syntax errors.