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Denormalization and basic guidelines for database design

Don Burleson EXPERT RESPONSE FROM: Don Burleson

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QUESTION POSED ON: 12 July 2004
What are the basic guidelines one should keep in mind while designing a database? Is denormalization always good?

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EXPERT RESPONSE

I used to teach database design in graduate school, and your question is excellent! The main purpose of high normalization was the reduction of disk space, back when it mattered in the 1970s.

Today, I always introduce redundancy into the model whenever it can eliminate an SQL join, but not always. I make my decision based on two criteria:

1 – The size of the redundant item

2 – The volatility of the item (e.g. how often do I need to duplicate updates)

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