When to use NULL in MySQL tables

Question

I appreciate the semantic meaning of a NULL value in a database table, different from both false and the empty string \'\'. However, I have often read about performance pro

Answer 1

As @ForYourOwnGood said - Null should be used for "unknown" information. For example: If you have a lot of fields that customer should fill-in on registration and some of them are optional. For some reason you might want to reserve an ID for that particular customer and since you don't know if the optional fields are a real choice by the customer to be left empty you should set them as NULL i.e. "unknown" when you first save the row. If the customer submits the form, passes all your validation and then you save the information, then you know for fact that the optional field is left empty by intention.

This is just a good case of using NULL.