MySQL NULL + disk space

[TruckStuff]

Earlier today I started investigating a simple question: does mySQL use any disk space to store NULL values? After RingTFM and Goggling, it seems that mySQL actually users MORE disk space for NULL values. 😕 If this is the case, it seems that it would actually be more efficient (from a storage space perspective) to NEVER use Null. This doesn't make a lot of sense to me because NULL is supposed to be "nothing".

I've read that columns with 'NOT NULL ' specified saves 1 bit per column, but it still doesn't jive as to how "nothing" is actually "something". 😕 Can anyone elaborate on this? TIA.

[pete_bisby]

I've always been lead to believe that NULL is not nothing, NULL is NULL. It is a searchable value and is distinctly different from nothing, which can be interpreted as a zero-length string or a zero.

I would have thought, though, that MySQL would have to allocate physical disk space for a NULLable attribute, for the possibility of a potential value. So, for a VARCHAR(255) attribute that is NULLable, it would still have to make room for 255 characters of data.