Issue with Running Total Still - sql-server

Question

I still have an issue with working out the best way to calculate a running balance.
I am going to be using this code in a Rent Statement that I am going to produce in SSRS, but the problem I am having is that I can't seem to work out how to achieve a running balance.
SELECT rt.TransactionId,
rt.TransactionDate,
rt.PostingDate,
rt.AccountId,
rt.TotalValue,
rab.ClosingBalance,
ROW_NUMBER()OVER(PARTITION BY rt.AccountId ORDER BY rt.PostingDate desc) AS row,
CASE WHEN ROW_NUMBER()OVER(PARTITION BY rt.AccountId ORDER BY rt.PostingDate desc) = 1
THEN ISNULL(rab.ClosingBalance,0)
ELSE 0 end
FROM RentTransactions rt
--all accounts for the specific agreement
INNER JOIN (select raa.AccountId
from RentAgreementEpisode rae
inner join RentAgreementAccount raa on raa.AgreementEpisodeId = rae.AgreementEpisodeId
where rae.AgreementId=1981
) ij on ij.AccountId = rt.AccountId
LEFT JOIN RentBalance rab on rab.AccountId = rt.AccountId AND rt.PostingDate BETWEEN rab.BalanceFromDate AND isnull(rab.BalanceToDate,dateadd(day, datediff(day, 0, GETDATE()), 0))
What this gives me are the below results- I have included the results below -
So my code is sorting my transactions in the order I want and also is row numbering them in the correct order as well.
Where the Row Number is 1 - I need it to pull back the balance on that account at that point in time, which is what I am doing....BUT I am then unsure how I then get my code to start subtracting the proceeding row - so in this case The current figure of 1118.58 would need the Total Value in Row 2 = 91.65 subtracted from it - so the running balance for row 2 would be 1026.93 and so on...
Any help would be greatly appreciated.

Answer 1

Assuming you have all the transactions being returned in your query you can calculate a running total using the over clause, you just need to start at the beginning of your dataset rather than working backwards from your current balance:
declare #t table(d date,v decimal(10,2));
insert into #t values ('20170101',10),('20170102',20),('20170103',30),('20170104',40),('20170105',50),('20170106',60),('20170107',70),('20170108',80),('20170109',90);
select *
,sum(v) over (order by d
rows between unbounded preceding
and current row
) as RunningTotal
from #t
order by d desc
Output:
+------------+-------+--------------+
| d | v | RunningTotal |
+------------+-------+--------------+
| 2017-01-09 | 90.00 | 450.00 |
| 2017-01-08 | 80.00 | 360.00 |
| 2017-01-07 | 70.00 | 280.00 |
| 2017-01-06 | 60.00 | 210.00 |
| 2017-01-05 | 50.00 | 150.00 |
| 2017-01-04 | 40.00 | 100.00 |
| 2017-01-03 | 30.00 | 60.00 |
| 2017-01-02 | 20.00 | 30.00 |
| 2017-01-01 | 10.00 | 10.00 |
+------------+-------+--------------+