SQL query result issue - sql

Question

The query is used to get balance of certain client
SELECT t.[InvoiceID], t.S_Type as Type,
t.Date, t.Debit, t.Credit, b.Balance
FROM Statement as t CROSS apply
(SELECT Balance = SUM(Debit) - SUM(Credit)
FROM Statement as x
WHERE (x.date < t.date or
x.date = t.date
) AND
x.InvoiceID = t.InvoiceID
AND x.CustID = t.CustID
) b
WHERE t.CustID ='2' and date between '2015-01-01' and '2016-01-12'
order by InvoiceID, Type desc, Date
out out i get
InvoiceID Type Date Debit Credit Balance
4 Sales Invoice 2015-06-09 520.00 0.00 520.00
4 Receipt Voucher 2016-01-04 0.00 520.00 0.00
6 Sales Invoice 2015-06-09 160.00 0.00 160.00
6 Receipt Voucher 2016-01-04 0.00 160.00 0.00
9 Sales Invoice 2015-06-09 850.00 0.00 850.00
9 Receipt Voucher 2016-01-04 0.00 850.00 0.00
13 Sales Invoice 2015-06-09 200.00 0.00 200.00
20 Sales Invoice 2015-07-11 1225.00 0.00 1225.00
176 Sales Invoice 2015-12-14 900.00 0.00 900.00
the issue is with with sales invoices # 13 20 176 its supposed to sum the debit of invoice and show in balance
so right out put should be like this
InvoiceID Type Date Debit Credit Balance
4 Sales Invoice 2015-06-09 520.00 0.00 520.00
4 Receipt Voucher 2016-01-04 0.00 520.00 0.00
6 Sales Invoice 2015-06-09 160.00 0.00 160.00
6 Receipt Voucher 2016-01-04 0.00 160.00 0.00
9 Sales Invoice 2015-06-09 850.00 0.00 850.00
9 Receipt Voucher 2016-01-04 0.00 850.00 0.00
13 Sales Invoice 2015-06-09 200.00 0.00 200.00
20 Sales Invoice 2015-07-11 1225.00 0.00 1425.00
176 Sales Invoice 2015-12-14 900.00 0.00 2325.00

Answer 1

I think the logic is slightly off in the subquery.
SELECT t.[InvoiceID], t.S_Type as Type,
t.Date, t.Debit, t.Credit, b.Balance
FROM Statement as t CROSS apply
(SELECT Balance = SUM(Debit) - SUM(Credit)
FROM Statement as x
WHERE x.CustID = t.CustID AND
(x.date < t.date or
x.date = t.date AND x.InvoiceID <= t.InvoiceID
)
) b
WHERE t.CustID ='2' and
date between '2015-01-01' and '2016-01-12'
ORDER BY InvoiceID, Type desc, Date;
In other words, the prioritization for the cumulative sum should be date first and then when the dates are the same, use the invoice.
This means that all your values are really being miscalculated, because each invoice is starting over (with your original logic). However, the earlier invoices are fully paid, so you don't see the issue with them.
Note: in more recent versions of SQL Server, this is much easier (and more efficient) with the cumulative sum syntax:
sum(debit - credit) over (partition by custid order by date, invoiceid)
Or, if debit and credit could take on NULL values:
sum(coalesce(debit, 0) - coalesce(credit, 0)) over (partition by custid order by date, invoiceid)