How to Query up Monthly Closing Balance on a Table of Transactions

Question

Probably a simple question for an analytics wizard, but I'm not there yet...
Suppose I have a table of financial transactions named TX with TX_DATE and TX_AMOUNT columns and that some months may not have any transactions (i.e., there are gaps). I would like to know the best query for returning the closing monthly balance with no gaps. I suspect it will involve a trick I saw on asktom.oracle.com for generating the list of months between two dates, some outer join cleverness, the use of SUM(TX_AMOUNT) OVER (ORDER BY TX_DATE) or something to generate the running account balance, and some magic to pluck out the last balance amount for each month.
The trick I saw from askTom for generating a gap-less list of months looked like:
with date_range as
(select to_date('1/1/2007','mm/dd/yyyy') mindt, sysdate maxdt from dual)
select level, add_months(mindt,level-1) dt
from date_range
connect by level <= months_between(maxdt,mindt)+1
(assuming in this case the range of tx dates was Jan 1, 2007 through today).
Any assistance would be greatly appreciated.
Thanks,
Bill

Answer 1

Sorry for the lack of clarity - by closing monthly balance, I mean I want the balance of the account as of the end of each month. So, you have to keep a running balance across the transactions (including a data point for months with no transactions) and then grab the running balance out for the latest transaction in each month. I have all but that last bit (which may be answered by another recent thread that I am reading). Here is what I have so far:
with date_range as
(select min(transaction_date) mindt, sysdate maxdt
from fz_transaction
where account_id = 320001
all_months as
(select level, add_months(mindt,level-1) dt
from date_range
connect by level <= months_between(maxdt,mindt)+1
gapless_transactions as
(select id, transaction_date, amount
from fz_transaction
where account_id = 320001
union all
select 1 id, dt transaction_date, 0 amount
from all_months
running_balance as
(select id, transaction_date, sum(amount) over (order by transaction_date, id) balance
from gapless_transactions
order by transaction_date desc, id desc
select * from running_balance
-- Working on this last part to pull out the last entry in each month...
Note that the UNION ALL in the gapless_transactions part throws in a bogus (but harmless in this computation) $0 transaction each month so I have no gaps in any month.
Perhaps there is a more elegant strategy, but I think I'm almost there...