declare @Transaction table

(

ID int

, Store char(3)

, SKU int

, AvailableQty int

, ReceivingStore char(3)

, QtyDemand int

)

insert into @Transaction

select 1, 'ST1', 100, 20, 'ST2', 14union all

select 2, 'ST1', 100, 20, 'ST3', 25union all

select 3, 'ST1', 100, 20, 'ST4', 25

select ID, Store, SKU, AvailableQty, ReceivingStore, QtyDemand , case when bal < 1 then

case when QtyDemand + bal < 0 then 0 else QtyDemand + bal end

else AvailableQty - bal end as transfered

from

(

select *

, (AvailableQty - SUM(t.QtyDemand ) OVER (Partition by sku ORDER BY ID ROWS UNBOUNDED PRECEDING)) as bal

from @Transaction t

) A

hope it helps.