enhancing master data

Hello Everyone,

I need to enhance the ds 0customer_attr with fields GRUPP and KDGRP from KNKK table. what is the logic that i need to use to fill the fields with data by also ensuring that i don't get any duplicate records for the fields. (the keys for the table KNKK --> KUNNR and KKBER).

P.S: How do i ensure whether i am getting duplicate records or not ?

Thanks in advance.