mySQL - Should I denormalise?

Question

Overview (Sorry its vague - I think if I went into more detail it would just over complicate things)

I have three tables, table one contain

Answer 1

My advice is to follow this general rule: Normalise by default, then denormalise if and when you identify a performance problem which it will solve.

I find normalised data, and code dealing with it, easier and more logical to maintain. I don't think there is any problem using denormalisation to improve performance, but I would not speculatively apply any performance optimisation which results in a decrease in maintainability until you are sure they are necessary.