Beginning Microsoft SQL Server 2008 ... - S3 Tech Training

Chapter 8: Being Normal: Normalization and Other Basic Design Issues
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A first pass on this might have one entity: Orders.
As you become more experienced at normalization, your first pass at something like this is probably
going to yield you quite a few more entities right from the beginning. For now though, we’ll just take
this one and see how the normalization process shows us the others that we need.
Assuming you’ve got your concepts down of what you want your entities to be, the next place to go is to
figure out your beginning columns and, from there, a primary key. Remember that a primary key provides
a unique identifier for each row.
We can peruse our list of columns and come up with key candidates. Your list of key candidates should
include any column that can potentially be used to uniquely identify each row in your entity. There is,
otherwise, no hard and fast rule on what column has to be the primary key (this is one of many reasons
you’ll see such wide variation in how people design databases that are meant to contain the same basic
information). In some cases, you will not be able to find even one candidate key, and you will need to
make one up (remember Identity and rowguid() columns?).
We already created an Orders table in the previous chapter, but for example purposes let’s take a look at
a very common implementation of an Orders table in the old flat file design:
Orders
OrderNo
CustomerNo
CustomerName
CustomerAddress
CustomerCity
CustomerState
CustomerZip
OrderDate
ItemsOrdered
Total
Since this is an Orders table, and logically, an order number is meant to be one to an order, I’m going go
with OrderNo as my primary key.
OK, so now we have a basic entity. Nothing about this entity cares about the ordering of columns (tables
are, by convention, usually organized as having the primary key as the first column(s), but, technically
speaking, it doesn’t have to be that way). Nothing in the basic makeup of this table cares about the
ordering of the rows. The table, at least superficially, describes just one entity. In short, we’re ready to
begin our normalization process (actually, we sort of already have).