Multiple Key fields in the Z-table

Hi all,

In the Z table the fields are Serial No , Customer Code, Credit limit Additonal Credit limit,

in that my User requires :

Sno Customer Code Creditlimit Addtional

1 10001 2000 2100

2 10001 1000 1010

1 10010 2012 25400

2 10010 1451 1524

1 10002 2312 2500

1 10020 4152 4500

1 10025 1245 2456

Like above shown for each Customer they need to give serial No from 1. i have defined serial no as primary key in the beginning now am attempting to give Customer Code also as Primary Key,

its not working.

Could you please tell me how to handle this scenario.

Thanks ,

rajesh S.