Database Normalization - First Normal Form (1NF) (Page 2 of 6 )
First Normal Form (1NF)
First Normal Form states that each attribute in a relation has to be atomic and scalar. It also states that a table must have a primary key to identify any particular row. You cannot store a list of values in a single column and you cannot store a list of columns that emulate a fixed size list - also known as a repeating group. For example, suppose you were to create a table to hold contact information for business contacts:
CREATE TABLE Contacts (
first_name*,
last_name,
company,
phone1,
phone2,
phone3,
fax,|
email
);
* Data types ellided
This table contains a repeating group - phone1-3. More often than not, several of those columns will be empty, which is a waste. It is also nearly impossible to enforce any uniqueness for this group because a constraint cannot be declared such that any phone1 is unique across phone1, phone2 and phone3.
Consider another set of problems - what if you want to add a company, not a person, to your Contacts table? Or just a phone number and a first name? You would have to leave one or more of the candidate key columns (first_name, last_name, company), which would most certainly violate the only possible primary key constraint. What if you want to delete a fax number from your table? If you simply DELETE WHERE fax=X, you may be deleting people as well.
Next: Second Normal Form (2NF) >>
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