Справочник Пользователя для Wiley Beginning ASP.NET 1.1 with Visual C# .NET 2003 978-0-7645-5708-8

This is the sort of thing you'd see in a spreadsheet, but there are a couple of big problems with this. For a
start, we have repeated information. John, for example, has his address shown three times. What 
happens if he moves house? You'd have to change the address everywhere it occurs. Dave has two
addresses, but notice they are slightly different. Which one is correct? Are neither correct?

To get around these problems, we use a process called Normalization.

Normalization

This is the process of separating repeated information into separate tables. There are whole books 
dedicated to database design, but we only need to look at the simplest case. A good beginner book on
database design is Database Design for Mere Mortals: A Hands On Guide to Relational Database Design, by
Michael J. Hernandez

What we need to do is split the previous table into three tables, one for each unique piece of information
– Customers, Orders, and OrderDetails. To link the three new tables together, we create ID columns
that uniquely identify each row. For example, we could create a column called CustomerID in the
Customers

table. To link the Customers table to the Orders table, we also add this CustomerID to the

Orders

table. Let's look at our tables now.

The Customers table is as follows:

The Orders table is as follows:

1

John

15 High Street 
Brumingham 
England UK 

2

Chris 

25 Easterly Way 
Cradiff  
Wales UK 

3

Dave

2 Middle Lane 
Oxborough 
England UK 

Dave

3 Middle 
Lane 
Oxborough
England  
UK

01/09/2003 

Thingamajig 

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Reading from Databases

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