Normalization and Query Performance

[Rizz84]

Hello Guys,
Basically I am doin a basic course in Database Design Management System in my BS I have read about normalization but had a problem in it. I want U guys to help me I need some technical specification regarding this topic.

My Query is:
"Database normalization is the process of organizing the fields and tables of a relational database to minimize redundancy and dependency. but as it removes anomalies form data it effect query performance and why does this happen???"

Take care:)

[ChrisPadgham]

one reason that it happens is that removing redundancy means that the redundant fields need to be recalculated each time they are required. take for example InvoiceTotal, the value is redundant because it is simply the sum of the InvoiceItem values. This means that instead of holding an Invoice Total in the database we sum the InvoiceItems each time we need to know the invoice total.

Thus we are doing many hits on the database instead of one.