-my $credit_sub = "SELECT SUM(amount) AS credit_amount, billpkgnum
- FROM cust_credit_bill_pkg $credit_where GROUP BY billpkgnum";
+my $credit_sub = "SELECT SUM(cust_credit_bill_pkg.amount) AS credit_amount, billpkgnum
+ FROM cust_credit_bill_pkg
+ JOIN cust_credit_bill USING (creditbillnum)
+ $credit_where
+ GROUP BY billpkgnum";