I am in the process of introducing the concept of primary keys to my data structures. I do not use databases at all. I will make use of a separate file to pull the keys from. My question is this ...

When I build files containing things which require unique keys, such as something like EXPENSE CATEGORIES in an accounting system, I usually have a unique code associated with a description (i.e. AUTO - Automobile Expense, etc ...). This is so ingrained into my thinking that recently when I began using Primary Keys, I had a file in which I inserted both a Primary Key AND the unique code which is associated with the description.

This seems redundant but before I take the leap and get rid of the unique code I would like some sort of supportive statements from this forum confirming that this is in fact the way to go or alerting me to some pitfalls to this path. Any comments ?