NULL and 0

[eluser]dimaomni[/eluser]
Hello everybody!

I have some input_form().From they I receive array which can include key with digits and empty values.

This values I use for INSERT query, and when value has NULL - this involve sql error.
So I start to use array_filter(), and everything had been good before I needed use "0".

I've tried use this condition, however it like tautology and don't work ).

Code:

if ($mark>=0 && $mark<=12 && $mark != NULL)

What do you tell ?