Microsoft SQL Server 2012 Bible

Normal Forms

Taking a detailed look at the normal forms moves this chapter into a more formal study of relational database design.

Contrary to popular opinion, the forms are not a progressive methodology, but they do represent a progressive level of compliance. Technically, you can't be in 2NF until 1NF has been met. Don't plan to design an entity and move it through a first normal form to a second normal form, and so on. Each normal form is simply a different type of data integrity fault to be avoided.

First Normal Form (1NF)

The first normalized form means the data is in an entity format, such that the following three conditions are met:

• Every unit of data is represented within scalar attributes. A scalar value is a value “capable of being represented by a point on a scale,” according to Merriam-Webster.

Every attribute must contain one unit of data, and each unit of data must fill one attribute. Designs that embed multiple pieces of information within an attribute violate the first normal form. Likewise, if multiple attributes must be combined in some way to determine a single unit of data, the attribute design is incomplete.

• All data must be represented in unique attributes. Each attribute must have a unique name and a unique purpose. An entity should have no repeating attributes. If the attributes repeat, or the entity is wide, the object is too broadly designed.

A design that repeats attributes, such as an order entity that includes item1, item2, and item3 attributes ...