Sum only the selected rows - sql

Question

The below query gets customer statement:
SELECT t.S_Type,t.Number, t.Debit, t.Credit,t.CustID,b.Balance
FROM Statement as t
CROSS apply
(
SELECT Balance = SUM(Debit) - SUM(Credit)
FROM Statement as x
WHERE x.Number<= t.Number
) b
ORDER BY t.Number
Query result:
type # Debit credit cid balance
Sales Invoice 1 200.00 0.00 3 200.00
Sales Invoice 10 850.00 0.00 3 1050.00
Service Invoice 11 90.00 0.00 21 1140.00
Sales Invoice 12 20.00 0.00 3 1160.00
Sales Invoice 13 200.00 0.00 2 1360.00
Sales Invoice 14 20.00 0.00 9 1380.00
Sales Invoice 15 120.00 0.00 17 1500.00
Sales Invoice 16 100.00 0.00 19 1600.00
Sales Invoice 17 140.00 0.00 20 1740.00
Sales Invoice 18 4250.00 0.00 16 5990.00
Sales Invoice 19 2500.00 0.00 22 8490.00
Sales Invoice 2 100.00 0.00 7 8590.00
Sales Invoice 20 1225.00 0.00 2 9815.00
Sales Invoice 3 200.00 0.00 1 10015.00
Sales Invoice 4 520.00 0.00 2 10535.00
Sales Invoice 5 25.00 0.00 1 10560.00
Sales Invoice 6 160.00 0.00 2 10720.00
Sales Invoice 7 20.00 0.00 7 10740.00
Sales Invoice 9 850.00 0.00 2 11590.00
But I'd like to get the statement for customer with id 7. The query I use for this is:
SELECT t.S_Type,t.Number, t.Debit, t.Credit,t.CustID,b.Balance
FROM Statement as t
CROSS apply
(
SELECT Balance = SUM(Debit) - SUM(Credit)
FROM Statement as x
WHERE x.Number<= t.Number
) b
where t.CustID='7'
ORDER BY t.Number
This query's result is:
type # Debit credit cid balance
Sales Invoice 2 100.00 0.00 7 8590.00
Sales Invoice 7 20.00 0.00 7 10740.00
However, that result is wrong. I expect it to be:
balance
100.00
120.00
What's wrong with the query?

Answer 1

To fix your query you need to add the CustID to the correlated cross apply so that the sum only is calculated for the customer in the outer scope and not for all:
SELECT t.S_Type, t.Number, t.Debit, t.Credit, t.CustID, b.Balance
FROM Statement AS t
CROSS APPLY
(
SELECT Balance = SUM(Debit) - SUM(Credit)
FROM Statement AS x
WHERE x.Number <= t.Number AND t.CustID = x.CustID
) b
WHERE t.CustID='7'
ORDER BY t.Number
If you're using SQL Server 2012+ a better alternative that also should perform better would be to use sum() as a window function:
SELECT
S_Type, Number, Debit, Credit, CustId,
Balance = SUM(Debit - Credit) OVER (PARTITION BY CustId ORDER BY Number)
FROM Statement
WHERE CustID='7'
ORDER BY Number
Your original query (without the where clause) would be:
SELECT
S_Type, Number, Debit, Credit, CustID,
Balance = SUM(Debit - Credit) OVER (ORDER BY number)
FROM Statement
ORDER BY Number

Answer 2

In CROSS APPLY add following in the WHERE:
AND x.CustID = t.CustID
Finally I got what you need. To make this you need to filter by customer also. Otherwise the cumulative balance is made on whole set and after that you show only customer 7.
After the change you will have cumulative balance only for customer 7.
Proper SQL:
SELECT t.S_Type,t.Number, t.Debit, t.Credit,t.CustID,b.Balance
FROM Statement as t
CROSS apply
(
SELECT Balance = SUM(Debit) - SUM(Credit)
FROM Statement as x
WHERE x.Number<= t.Number and x.CustID = t.CustID
) b
where t.CustID='7'
ORDER BY t.Number