How to Sum previos rows summatory to find a balance in SQL Server - sql

Question

I'm working on a service that needs to calculate how much a customer owes, according to a total invoice value and the partial payments that the customer has made.
So, in a tableA I have a row with the invoice total value:
[dbo].[TableA]
ID CustomerId InvoiceVal
1 12 1000
2 11 2000
3 10 5000
4 14 15000
5 12 100
6 16 8000
7 18 3200
In a TableB I have the record of each customer's partial payments they have made to each invoice:
[dbo].[TableB]
ID InvoiceId Payment
1 1 150
2 3 50
3 1 120
4 1 100
5 5 90
6 4 7500
So, as you can see, the customer 12 has an invoice for $1000 and has made 3 payment that sum $370
I need to be able to se the partial total owed in each row, this is the expected result:
No. InoviceId CustomerId Payment Owed
1 1 12 150 850
2 1 12 120 730
3 1 12 100 630
So far, this is my code:
DECLARE #invid int = '1'
DECLARE #invoicetotal numeric(18,2)
SET #invoicetotal =
(
SELECT
[dbo].[TableA].[InvoiceVal]
FROM [dbo].[TableA]
WHERE
([dbo].[TableA].[ID] = #invid)
)
SELECT
*,
SUM(#invoicetotal - [dbo].[TableB].[Payment]) OVER(ORDER BY [dbo].[TableB].[ID] ROWS BETWEEN UNBOUNDED PRECEDING AND 1 PRECEDING) AS [Owed]
FROM [dbo].[TableB]
WHERE
([dbo].[TableB].[InvoiceId] = #invid)
But this is what I get:
ID InvoiceId Payment Owed
1 1 150.00 NULL
3 1 120.00 850.00
4 1 100.00 1730.00
I need to sum the previous payment on each row.
Thanks!

Answer 1

Something like this would help
SELECT
ROW_NUMBER() OVER (ORDER BY TableB.ID ASC) NO,
CustomerId,
Payment,
InvoiceVal - SUM(Payment) OVER (PARTITION BY TableA.ID ORDER BY TableB.Id ASC) Owed
FROM TableA
INNER JOIN TableB
ON TableA.Id = TableB.InvoiceId
WHERE
CustomerId = 12
Working Fiddle

Answer 2

Your query will depend on what you are trying to make as your final output.
If you want just ONE CustomerID, go with:
SELECT a.ID AS InvoiceID, a.CustomerID, a.InvoiceVal AS StartInvoice
, b.ID AS bid, b.Payment
, a.InvoiceVal - ISNULL(SUM(b.Payment) OVER (PARTITION BY a.ID ORDER BY b.id),0) AS owed
FROM TableA a
LEFT OUTER JOIN TableB b ON a.ID = b.InvoiceID
WHERE a.CustomerID = 12
And if that CustomerID doesn't have any payments, you want to use a LEFT JOIN so that you don't eliminate an amount owed.
SELECT a.ID AS aid, a.CustomerID, a.InvoiceVal AS StartInvoice
, b.ID AS bid, b.Payment
, a.InvoiceVal - ISNULL(SUM(b.Payment) OVER (PARTITION BY a.ID ORDER BY b.id),0) AS owed
FROM TableA a
LEFT OUTER JOIN TableB b ON a.ID = b.InvoiceID
WHERE a.CustomerID = 11
I also added an ISNULL() around Payment to keep from nulling out your owed amount. It could also be added to the InvoiceVal to account for a CustomerID who hasn't been invoiced yet, if that was needed (or possible from other tables).
IF you want to get ALL CustomerIDs, you'll have to account for that in your partition.
SELECT s1.CustomerID, aid AS InvoiceID, s1.bid, s1.Payment
, (s1.StartInvoice - s1.runningPayment) AS Owed
FROM (
SELECT a.ID AS aid, a.CustomerID, a.InvoiceVal AS StartInvoice
, b.ID AS bid, b.Payment
, ISNULL(SUM(b.Payment) OVER (PARTITION BY a.CustomerID, a.ID ORDER BY b.id),0) AS runningPayment
FROM TableA a
LEFT OUTER JOIN TableB b ON a.ID = b.InvoiceID
) s1
ORDER BY s1.CustomerID, s1.aid, s1.bid
Fiddle demonstrates overpayment or paying total balance for 0 owed.