Tweaking a SUM query

Question

Hello experts,
I'm working on Oracle 10g. My query needs to sample out accounts for whom, payment has been processed ( using "tracking_id" ).
Current Table structure with sample data:
Table BM -- around 7 million records
account_no | balance_due
12345 | 200
12345 | 100
12346 | 0
12346 | 99.0
Table BALANCE - 6.75 million records
account_no | tracking_id
12345 | 72422000
12345 | 72422010
12346 | 72422009
12346 | 72422020
I use the following Query to sample out the accounts for which payment has been processed along with their balances. The data is structured, such that, at any given time, the actual balance of the customer is the sum of all values in the " balance_due " field
create table paid29 as
select a1.account_no, sum(a2.balance_due) postpaid_balance
from BM a1, BALANCE a2
where a1.tracking_id between 72421000 and 72422050 and
a1.account_no = a2.account_no
group by a1.account_no; My query seems to work perfectly when the account_no's are distinct for a given payment cycle. However when there is more than one payment for a particular account ( there will be 2 tracking_id in this case for the same account) , my query seem's to be summing up the "balance_due" twice, instead of just summing up once before performing an insert. resulting in mis-match during reconciliation.
Any help to get around this problem will be very helpful. I've tried my best to be clear with my requirements. Please let me know if anymore info is required to help me fix the query.
Current Result:
Table paid29
account_no | balance_due
12345 | 600.0
12346 | 198.0
Expected Result:
Table paid29
account_no | balance_due
12345 | 300.0
12346 | 99.0
Regards,
novice.

Answer 1

You are running into Cartesian product.
Try something like:
SQL> With BALANCE as
  2  (
  3  SELECT 12345 account_no , 200 balance_due FROM Dual
  4  UNION ALL
  5  SELECT 12345 , 100 FROM Dual
  6  UNION ALL
  7  SELECT 12346 , 0 FROM Dual
  8  UNION ALL
  9  SELECT 12346 , 99.0 FROM Dual
10  ),
11  BM as
12  (
13  SELECT 12345 account_no, 72422000 tracking_id FROM Dual
14  UNION ALL
15  SELECT 12345 , 72422010 FROM Dual
16  UNION ALL
17  SELECT 12346 , 72422009 FROM Dual
18  UNION ALL
19  SELECT 12346 , 72422020 FROM Dual
20  )
21  -- end of test data
22  SELECT   a1.account_no, SUM (a2.balance_due) postpaid_balance
23      FROM (SELECT DISTINCT account_no
24                       FROM bm
25                      WHERE tracking_id BETWEEN 72421000 AND 72422050) a1,
26           balance a2
27     WHERE a1.account_no = a2.account_no
28  GROUP BY a1.account_no;
ACCOUNT_NO POSTPAID_BALANCE
     12346               99
     12345              300
2 rows selected.
SQL> Hope this helps.
Regards,
Jo