Really Really Weird Problem

Question

Hi All,
I have the following query:
SELECT *
FROM
fin_payment,
s1_name_and_address s1_name_and_address_b,
s1_currency
WHERE (fin_payment.internal_flag = 'N' or fin_payment.internal_flag is null )
AND fin_payment.bank_id = s1_name_and_address_b.name_and_address_id
AND fin_payment.currency_code = s1_currency.currency_code
AND (('P' = 'C' and fin_payment.check_reference is not null )
OR
('P' = 'P' and fin_payment.advice_nbr is not null )
AND fin_payment.financial_source = 'A/P'
AND fin_payment.payment_type = 'L'
AND ('P' is null or 'P' = 'A' );
It shouldn't return any rows because of that condition which is bold: ('P' is null or 'P' = 'A' ), because it's always false. The problem is if I remove that condition and paste it in the middle of where cluse like this:
SELECT
NULL,
NULL,
fin_payment.bank_id,
s1_name_and_address_b.full_name,
fin_payment.check_reference,
fin_payment.payment_date,
fin_payment.bank_amount,
fin_payment.currency_code,
s1_currency.description,
fin_payment.payment_nbr,
fin_payment.payment_type,
fin_payment.invoice_nbr,
fin_payment.ap_check_reference_nbr ,
fin_payment.reconciliation_status ,
fin_payment.replacement_payment_nbr ,
fin_payment.advice_nbr
FROM
fin_payment,
s1_name_and_address s1_name_and_address_b,
s1_currency
WHERE (fin_payment.internal_flag = 'N' or fin_payment.internal_flag is null )
AND fin_payment.bank_id = s1_name_and_address_b.name_and_address_id
AND fin_payment.currency_code = s1_currency.currency_code
AND (('P' = 'C' and fin_payment.check_reference is not null )
OR
('P' = 'P' and fin_payment.advice_nbr is not null )
AND ('P' is null or 'P' = 'A' )
AND fin_payment.financial_source = 'A/P'
AND fin_payment.payment_type = 'L'
it will return some rows which is wrong. I don't know how it generate those rows. Because if you remove that condition, I mean ('P' is null or 'P' = 'A' ), it doesn't retrieve any rows.
And another thing is, it just happen in Oracle 9.0.1 not in other versions like 8.0.5, 8.1.5,8.1.6...
any help is greatly appreciated,
Arash

Answer 1

No Justin. For making the query easier I wrote that condition (P is null or ....) like that. and s1_name_and_address is an alias.
I thought the data or tabel is corrupted, so I created a new table as
"create table test select * from fin_payment"
no for the same query, I get two diference result on table Test & fin_payment !?
I really don't have any idea !