I am somewhat new to VBA

I am try to achieve what essential Access table can do.
I have an inventory table, Excel table inserted such as below(it's a table, not a listing)
Column A = Product Code
Column B = Description
Column C,D,E,etc = other characteristic/attributes
My ultimate goal is to avoid same product code being used more than once with different attribute or the same attribute.
perhaps a msgbox when a duplicate entry occurred or disallow the current entry with a msgbox stating duplicate entry detected.
Any help would be appreciated.