Is it really better to use normalized tables?

Question

I heard my team leader say that in some past projects they had to do away with normalization to make the queries faster.

I think it may have something to do with table unions.

Is having more lean tables really less efficient than having few fat tables?

Answer 1

It depends ... joining tables is inherently slower than having one big table that is 'pre-joined' ie de-normalised. However, by denormalising you're going to create data duplication and your tables are going to be larger. Normalisation is seen as a good thing, because it creates databases that can answer 'any' question, if it is properly done you can build a select to get to your data. This is not the case in some other forms of DB, and those are now (mostly) historic irrelevancies, the normalised/relation DB won that battle.

Back to your question, using de-normalisation to make things go faster is a well accepted technique. It's normally best to run your DB for a while so you know what to de-normalise and what to leave alone, and it's also common to leave the data in its 'correct' normalised form and pull data into a set of de-normalised reporting tables on a regular basis. If that process is done as part of the report run itself then the data is always up to date too.

As an example of over-normalisation I've seen DBs in the past where the days of the week, and months of the year were pulled out into separate tables - dates themselves were normalised - you can go too far.