The script below can be used to find credit numbers that are duplicated for vendors
select Vendor_Code,
b.Credit_Number, Count(b.Credit_Number) as "Number of Credits with Duplicate Credit Number"
from AP_Vendor a, AP_Credit b
where a.Vendor_Id = b.Vendor_Id
Group by a.vendor_code, b.Credit_Number
having count(b.Credit_Number) >1
