How do you determine how far to normalize a database?

Question

When creating a database structure, what are good guidelines to follow or good ways to determine how far a database should be normalized? Should you create an un-normalized

Answer 1

I agree that you should normalise as much as possible and only denormalise if absolutely necessary for performance. And with materialised views or caching schemes this is often not necessary.

The thing to bare in mind is that by normalising your model you are giving the database more information on how to constrain your data so that you can remove the risk of update anomalies that can occur in incompletely normalised models.

If you denormalise then you either need to live with the fact that you may get update anomolies or you need to implement the constraint validation yourself in your application code. This takes away a lot of the benefit of using a DBMS which lets you define these constraints declaratively.

So assuming the same quality of code, denormalising may not actually give you better performance.

Another thing to mention is that hardware is cheap these days so throwing extra processing power at the problem is often more cost effective than accepting the potential costs of cleaning up corrupted data.