In MySQL, I have a visitor_log table that looks like this...

------				-----	--------
id (UK)				No
member_viewed_id (P1)(FK)	No
visitor_id (P2)(FK)		No	0
ip				No
hostname			No
created_on (P3)			No
updated_on			Yes

Based on some previous advice, I was told that is it okay to store a NULL in the "visitor_id" field when someone is a non-registered Visitor.

In phpMyAdmin, I changed the "visitor_id" field to Null = "Yes" and left Default blank, but when I save the table phpMyAdmin is not accepting these changes?!

What is wrong?

And how do I make it so I can INSERT a NULL into the "visitor_id" field when logging a Non-Member Visitor?



P.S. Because I used to INSERT a "0" for Non-Member Visitors, my table has tons of records with visitor_id = 0. But that shouldn't matter if I am just trying to make the field Nullable?!