There was a small typo. The query will be:
SELECT * FROM
(
SELECT T0."DocNum", T0."DocTotal", T1."DocNum", T1."DocTotal" FROM OPOR T0, OPOR T1 WHERE T0."DocTotal" = T1."DocTotal"
)
WHERE T0."DocNum" <> T1."DocNum"
To consider the other fields you have to just add them in the where condition with "and" clause with the same condition.
Regards,
Amit