The Normal Forms: In a Nutshell
In this series, I have tried to explain in non-mathematical terms what the first three Normal Forms mean and how they determine database design.
This is not the most useful method of learning normalization. In fact, many expert developers never learn the formal definition of the normal forms. If you haven't already, I suggest you read the following series:
However, I think it is useful to know what the Normal Forms are. Sometimes when you get stuck in a design, you can go back to the definitions to get yourself out of trouble.
So, in summary:
First Normal Form (1NF) says that each record must be unique, that is, it has a primary key. There are some additional restrictions on how such uniqueness is maintained such as not allowing positional referencing and no repeated columns.
Second Normal Form (2NF) says that each field in the record must depend on the whole primary key, not just a part of it.
Third Normal Form (3NF) says that no field must depend on any other field except the primary key.
William Kent, author of A Simple Guide to Five Normal Forms in Relational Database Theory, once abbreviated the first three normal forms like this:
"The Key, the whole Key, and nothing but the Key, so help me Codd."