Lookup table

I have a table customer with two fields customerid and
customer name.
There is one more table sales with customerid and customer
name in it.
The relationship is one to many ( Customer to sales )

Now this is what I want to be working in table.
As soon as I enter a new record with the customer id in
sales table it should get the customer name from customer
table and fill up the customer name field of sales table.

I know this is not a correct design but is it possible?


Any suggestions will be highly appreciated.
Thanks,
San