NULL in MySQL (Performance & Storage)

Question

What exactly does null do performance and storage (space) wise in MySQL?

For example:

TINYINT: 1 Byte TINYINT w/NULL 1 byte + somehow stores NULL?

Answer 1

I would agree with Bill Karwin, although I would add these MySQL tips. Number 11 addresses this specifically:

First of all, ask yourself if there is any difference between having an empty string value vs. a NULL value (for INT fields: 0 vs. NULL). If there is no reason to have both, you do not need a NULL field. (Did you know that Oracle considers NULL and empty string as being the same?)

NULL columns require additional space and they can add complexity to your comparison statements. Just avoid them when you can. However, I understand some people might have very specific reasons to have NULL values, which is not always a bad thing.

On the other hand, I still utilize null on tables that don't have tons of rows, mostly because I like the logic of saying NOT NULL.

Update Revisiting this later, I would add that I personally don't like to use 0 instead of NULL in the database, and I don't recommend it. This can easily lead to a lot of false positives in your application if you are not careful.