Try following code. IIF should give you correct cust_id and NVL'll convert .Null. into 0

SELECT ;
	IIF( ISNULL(tCredit.cust_id1), tDebit.cust_id1, tCredit.cust_id1) AS cust_id1, ;
	IIF( ISNULL(tCredit.cust_id1), tDebit.cust_id2, tCredit.cust_id2) AS cust_id2, ;
	NVL(tDebit.amt, 0) AS Debitamt, NVL(tCredit.amt,0) AS Creditamt ;
	FROM tCredit ;
	FULL OUTER JOIN tDebit ON tCredit.cust_id1 = tDebit.cust_id1 ;
				AND tCredit.cust_id2 = tDebit.cust_id2 ;
	INTO CURSOR CredIDebit						

>I have two tables: tCredit and tDebit. Each has three fields: cust_id1, cust_id2, amt. Want to produce a table that has cust_id1, cust_id2, credit_amt, debit_amt.
>
>There are cust_id1/cust_id2 records in tCredit that are not tDebit and visa versa. So they would have 0 in the non-matching amount field.
>
>I tried a FULL OUTER JOIN but could not get the cust_id1/cust_id2 to have a value for both the tCredit and tDebit non-matches.
>
>Thanks
>
>Brenda