Good article.. Thanks!..

Here is how I would have solve the problem.

UPDATE a

SET a.netInventoryQty=c.inventoryQty-b.cQty

--SELECT *

FROM demand a

INNER JOIN (

select a.demandID, sum(b.orderQty) as cQty

FROM demand a

INNER JOIN demand b ON b.demandID<=a.demandID AND b.itemID=a.itemID

GROUP BY a.demandID

) b on b.demandID=a.demandID

INNER JOIN Inventory c ON c.itemID=a.itemID

I'll have to check out if your method is faster.

Thanks again