Sql server View with while statement - sql

Question

I`m learning to use SQL and this is my second question, hope it make sense! :)
My problem:
When I check a customer’s order, I need to know If it would be fully allocated (pre-shipped ) or not.
The DB hasn’t the progression of the allocated quantity, but only the allocated quantity for each order, and the total ordered to-be-allocated from the customers.
The orders will be allocated by: order priority, confirmation date, internal order number.
This is where I get so far:
SELECT dbo.MA_SaleOrdDetails.Item, dbo.MA_SaleOrdDetails.Description,
dbo.MA_SaleOrdDetails.Qty, dbo.MA_SaleOrdDetails.Allocated,
CASE WHEN dbo.MA_SaleOrdDetails.Allocated > dbo.MA_SaleOrdDetails.DeliveredQty
THEN dbo.MA_SaleOrdDetails.Qty - dbo.MA_SaleOrdDetails.DeliveredQty - dbo.MA_SaleOrdDetails.Allocated
ELSE dbo.MA_SaleOrdDetails.Qty - dbo.MA_SaleOrdDetails.DeliveredQty END AS TOALLOCATE,
dbo.MA_SaleOrd.InternalOrdNo, dbo.MA_SaleOrd.ConfirmedDeliveryDate,
dbo.MA_SaleOrd.Customer, dbo.MA_SaleOrd.Priority,
dbo.MA_SaleOrdDetails.SaleOrdId, dbo.MA_SaleOrdShipping.Carrier1,
dbo.MA_SaleOrdShipping.ShipToAddress,
dbo.MA_ItemsFiscalData.FinalOnHand AS InitialAvailability
FROM dbo.MA_SaleOrdDetails
INNER JOIN dbo.MA_SaleOrd
ON dbo.MA_SaleOrdDetails.SaleOrdId = dbo.MA_SaleOrd.SaleOrdId
INNER JOIN dbo.MA_SaleOrdShipping
ON dbo.MA_SaleOrd.SaleOrdId = dbo.MA_SaleOrdShipping.SaleOrdId
INNER JOIN dbo.MA_ItemsFiscalData
ON dbo.MA_ItemsFiscalData.Item = dbo.MA_SaleOrdDetails.Item
WHERE (dbo.MA_SaleOrdDetails.Delivered = '0')
AND (dbo.MA_SaleOrdDetails.Invoiced = '0')
AND (dbo.MA_SaleOrdDetails.Cancelled = '0')
AND (dbo.MA_ItemsFiscalData.FiscalYear = YEAR(GETDATE()))
ORDER BY dbo.MA_SaleOrdDetails.Item, dbo.MA_SaleOrd.Priority,
dbo.MA_SaleOrd.ConfirmedDeliveryDate, dbo.MA_SaleOrd.InternalOrdNo
Now I want to calculate at each row in a new column named “progression” the progression of the quantity that will be allocated.
The progression should be:
For the first listed item = InitialAvailability – TOALLOCATE
For every row with same item = previous TOALLOCATE – TOALLOCATE
And restart every item change
I’ve tried with a WHILE statement but I could not make it work.
Im all yours :)