Only get rows until qty total is met - sql

Question

I have an order table (product, qty_required) and a stock/bin location table (product, bin_location, qty_free) which is a one->many (a product may be stored in multiple bins).
Please, please (pretty please!) Does anybody know how to:
When producing a picking report, I only want to return the first x bins for each product ordered THAT SATISFIES the qty_required on the order.
For example
An order requires product 'ABC', QTY 10
Product 'ABC' is in the following locations (this is listed using FIFO rules so oldest first):
LOC1, 3 free
LOC2, 4 free
LOC3, 6 free
LOC4, 18 free
LOC5, 2 free
so. on the report, I'd ONLY want to see the first 3 locations, as the total of those (13) satisfies the order quantity of 10...
Ie:
LOC1, 3
LOC2, 4
LOC3, 6

Answer 1

Use sum(qty_free) over(partition by product order by placement_date desc, bin_location) to calculate running sum and filter rows by your threshold in outer query (select from select). Added location in order by to exclude sum of all locations where placement was in the same day.
with s as (
select st.*,
sum(qty_free) over(partition by product order by placement_date asc, bin_location) as rsum
from stock st
)
select
o.product,
s.bin_location,
s.qty_free,
o.qty_requested
from orders o
left join s
on o.product = s.product
and s.rsum <= o.qty_requested
UPD: Since that turned out that your SQL Server version is so old that there's no analytic function in it, here's another less performant way to do this (maybe need some fixes, didn't tested on real data).
And fiddle with some setup.
with ord_key as (
select stock.*,
/*Generate order key for FIFO*/
row_number() over(order by
placement_date desc,
bin_location asc
) as sort_order_key
from stock
)
, rsum as (
/*Calculate sum of all the items before current*/
select
b.product,
b.bin_location,
b.placement_date,
b.qty_free,
coalesce(sum(sub.item_sum), 0) as rsum
from ord_key as b
left join (
/*Group by partition key and orderby key*/
select
product,
sort_order_key,
sum(qty_free) as item_sum
from ord_key
group by
product,
sort_order_key
) as sub
on b.product = sub.product
and b.sort_order_key > sub.sort_order_key
group by
b.product,
b.bin_location,
b.placement_date,
b.qty_free
)
, calc_quantities as (
select
o.product,
s.placement_date,
s.bin_location,
s.qty_free,
s.rsum,
o.qty_requested,
case
when o.qty_requested > s.rsum + s.qty_free
then s.qty_free
else s.rsum + s.qty_free - o.qty_requested
end as qty_to_retrieve
from orders o
left join rsum s
on o.product = s.product
and s.rsum < o.qty_requested
)
select
s.*,
qty_free - qty_to_retrieve as stock_left
from calc_quantities s
order by
product,
placement_date desc,
bin_location desc