Cumulative substract throught multiple rows - sql

Question

I would like to substract one row from multiple rows. I need to get remaining Quantity (differentiated by BusTransaction_ID and Artikl, and ordered by X_PDateMonth$DATE), which is result of this substract:
And expected results:
Result can be with or without "zero rows". I don't know, how to accomplish this result. And will be better use some "stored procedure" or something, because it will be use to a pretty large data set?
Thanks for all replies.

Answer 1

Here is a solution that works by doing the following:
Calculates the cumulative sums of the values in the first table.
Based on the cumulative sum, determines the value to subtract.
The query looks like this:
select t.bustransaction_id, t.artikl, t.xpldate,
(case when cumeq <= subt.quantity then 0
when cumeq - t.quantity <= subt.quantity
then cumeq - subt.quantity
else t.quantity
end) as newquantity
from (select t.*,
sum(quantity) over (partition by bustransaction_id, artikl order by xpldate) as cumeq
from start_table t
) t left join
subtract_table subt
on t.bustransaction_id = subt.bustransaction_id and
t.artikl = subt.artikl
order by t.bustransaction_id, t.artikl, t.xpldate;
Here is the SQL Fiddle (based on Brians).

Answer 2

This will give you the result with the 'zero rows' using analytic functions:
select x.*,
case
when subqty >= runner
then 0
when runner > subqty
and lag(runner, 1) over( partition by bustransaction_id, artikl
order by bustransaction_id, artikl, xpldate ) > subqty
then quantity
else runner - subqty
end as chk
from (select s.bustransaction_id,
s.artikl,
s.xpldate,
s.quantity,
sum(s.quantity) over( partition by s.bustransaction_id, s.artikl
order by s.bustransaction_id, s.artikl, s.xpldate ) as runner,
z.quantity as subqty
from start_table s
join subtract_table z
on s.bustransaction_id = z.bustransaction_id
and s.artikl = z.artikl) x
order by bustransaction_id, artikl, xpldate
Fiddle: http://sqlfiddle.com/#!6/20987/1/0
The CASE statement combined with the LAG function is what identifies the first "half-depleted" row, which is the biggest piece of your calculation.
In that fiddle I included my derived columns that were necessary to get what you wanted. If you don't want to show those columns you can just select those you need from the inline view, as shown here: http://sqlfiddle.com/#!6/20987/2/0