Is_Unique validation with custom db table

[eluser]wehappyfew[/eluser]
Hi
i've been educating myself on normalization and i must admit that it is right for my case.
Although my application is not going to be the next twitter, there would be just too many tables!

Though ,I have some questions...
1. should i have a separate id column for every table, like client_id,supplier_id or can I ,in some cases, use as an id ..lets say a column that has unique values like country_code -> DE.
in the countries table isn't it redundant to have both country_id and country_code?

2.the CRUD queries are going to be simpler that way? Or should i learn JOINS really well? I would prefer to be able to enjoy the benefits of CI's ActiveRecord class and harvest the flexibility of its queries.