SQL Joins vs Single Table : Performance Difference?

Question

I am trying to stick to the practice of keeping the database normalized, but that leads to the need to run multiple join queries. Is there a performance degradation if many quer

Answer 1

We leave query optimisation up to the database for the same reasons we leave code optimisation up to the compiler.

Most modern RDBMSes are pretty good in this respect these days.

Before you think that denormalisation is 'ok' in some cases, consider this: normally you are not interested in every attribute. Therefore loading unneeded data off the disk is inefficient (typically the least efficient component of the database). This can be much worse if you have a denormalised design, with lots of redundant data in a row. Even worse again if you have to then update all that redundant data. It can be much more efficient to load some narrow tables containing only the columns of interest and join them. Again, this depends on the database, so without profiling you have no clue.

If you are really worried about performance, you're probably talking scalability issues. In this case you might want to look at sharding, for which proper (normalised) schema design is important.