Here is database design:


What I want is:

If a visitor visits the page, check whether he's ip exists in the database

If he's ip exists and the member_name field is empty
echo "Your a Guest";

If he's ip exists and the member_name is filled with any text
echo "Your a member";

else
echo "your not logged in";

Use Cookies.

are you using an IP as a unique identifier?

Remember IP's don't necessarily identify the user's machine

IP is not static for many users. Using cookies is a better solution.