PHP short unique ID generation using auto_increment?

Question

I would like to generate a short, unique ID without having to check for collisions.

I currently do something like this, but the ID I currently generate is random and che

Answer 1

An MD5 of an incrementing number should be fine, but I worry that if you're truncating your MD5 (which is normally 128 bits) down to 5-8 characters, you will almost certainly be damaging it's capability to act as a unique signature...