Creating Ageing report (>0), (0-30), (31-60) - sql-server

Question

I am trying to write an Ageing Report on SQL Server which shows the total amount of overdue invoices (later on I will have to deduct Credit Notes) that fall in the different columns depending on how many days the have been overdued. I.e (>0), (0-30), (31-60), (61-90), etc.
This is the part of the query I have written so far mostly looking at old post in this forum but it's giving me a lot of duplicates even for Accounts where there is not due balance.
Any idea what I am doing wrong?
SELECT O.cardcode AS [Account],
O.cardname AS [Name],
O.u_creditlimit AS [Credit Limit],
O.u_onhold AS [On Hold],
O.balance,
Isnull(CASE
WHEN Datediff(day, INV.docduedate, Getdate()) >= 0 AND Datediff(day, INV.docduedate, Getdate()) < 30
THEN (
SELECT Sum(doctotal)
FROM oinv
WHERE cardcode = INV.cardcode)
END, 0) AS [0 to 30 Days],
Isnull(CASE
WHEN Datediff(day, INV.docduedate, Getdate()) >= 31 AND Datediff(day, INV.docduedate, Getdate()) < 60
THEN (
SELECT Sum(doctotal)
FROM oinv
WHERE cardcode = INV.cardcode)
END, 0) AS [31 to 60 Days],
Isnull(CASE
WHEN Datediff(day, INV.docduedate, Getdate()) >= 61 AND Datediff(day, INV.docduedate, Getdate()) < 90
THEN (
SELECT Sum(doctotal)
FROM oinv
WHERE cardcode = INV.cardcode)
END, 0) AS [61 to 90 Days],
Isnull(CASE
WHEN Datediff(day, INV.docduedate, Getdate()) >= 91 AND Datediff(day, INV.docduedate, Getdate()) < 120
THEN (
SELECT Sum(doctotal)
FROM oinv
WHERE cardcode = INV.cardcode)
END, 0) AS [91 to 120 Days],
Isnull(CASE
WHEN Datediff(day, INV.docduedate, Getdate()) >= 121
THEN(
SELECT Sum(doctotal)
FROM oinv
WHERE cardcode = INV.cardcode)
END, 0) AS [121+ Days]
FROM ocrd O
INNER JOIN oinv INV
ON O.cardcode = INV.cardcode
WHERE territory = 3
AND INV.docstatus = 'O'
Thank you very much.

Answer 1

You can clean this up a bit
First. use a CROSS APPLY to calculate the Days-Past-Due once, and then a conditional aggregation for the final results
Example (Untested)
Select O.cardcode
,O.cardname
,[Credit Limit] = max(O.u_creditlimit)
,[On Hold] = max(O.u_onhold)
,[0 to 30 Days] = sum( case when DPD between 0 and 30 then doctotal else 0 end)
,[31 to 60 Days] = sum( case when DPD between 31 and 60 then doctotal else 0 end)
,[61 to 90 Days] = sum( case when DPD between 61 and 90 then doctotal else 0 end)
,[91 to 120 Days] = sum( case when DPD between 91 and 120 then doctotal else 0 end)
,[121+ Days ] = sum( case when DPD >=121 then doctotal else 0 end)
From ocrd O
Join oinv INV on O.cardcode = INV.cardcode
Cross Apply (values ( Datediff(day, INV.docduedate, Getdate()) ) ) P(DPD)
Where territory = 3
and INV.docstatus = 'O'
and DPD >= 0
Group By O.cardcode
,O.cardname
EDIT - CREDIT NOTES
Without sample data or structures here is my GUESS
Select O.cardcode
,O.cardname
,[Credit Limit] = max(O.u_creditlimit)
,[On Hold] = max(O.u_onhold)
,[0 to 30 Days] = sum( case when DPD between 0 and 30 then doctotal - isnull(creditnotes,0) else 0 end)
,[31 to 60 Days] = sum( case when DPD between 31 and 60 then doctotal - isnull(creditnotes,0) else 0 end)
,[61 to 90 Days] = sum( case when DPD between 61 and 90 then doctotal - isnull(creditnotes,0) else 0 end)
,[91 to 120 Days] = sum( case when DPD between 91 and 120 then doctotal - isnull(creditnotes,0) else 0 end)
,[121+ Days ] = sum( case when DPD >=121 then doctotal - isnull(creditnotes,0) else 0 end)
From ocrd O
Join oinv INV on O.cardcode = INV.cardcode
LEFT JOIN CREDITNOTESTable CN ON O.cardcode = CN.cardcode
Cross Apply (values ( Datediff(day, INV.docduedate, Getdate()) ) ) P(DPD)
Where territory = 3
and INV.docstatus = 'O'
and DPD >= 0
Group By O.cardcode
,O.cardname

Answer 2

when asking questions is a great idea to provide demo data, and a better one to provide it as an object we can easily re recreate:
DECLARE #table TABLE (RecordID INT IDENTITY, CardCode INT, CardName NVARCHAR(100), u_CreditLimit DECIMAL(10,2), u_onhold DECIMAL(10,2), balance DECIMAL(10,2))
INSERT INTO #table (CardCode, CardName, u_CreditLimit, u_onhold, balance) VALUES (1, 'John Smith', 10000, 0, 200),
(1, 'John Smith', 10000, 0, 400),
(1, 'John Smith', 10000, 0, 200)
This would allow someone to just run the TSQL to create and populate the object.
Now using that object we could write something like
SELECT RecordID, CardCode, CardName, U_CreditLimit, U_OnHold, Balance, COALESCE(LAG(Balance,1) OVER (PARTITION BY CardCode ORDER BY RecordID) - Balance,Balance) AS RunningTotal
FROM #table
This psudeo code, and may need some tweaking to get exactly what you're looking for.
A quick word on LAG and its pal LEAD. You specify a column and an offset in rows. LAG looks backwards, LEAD forwards. They both use over clauses just like any other windowed function.