mysql and forms help

[Anon]

I'm working on a code that allows people to add comments to reviews posted on my website.

The comments are submitted via form, and the following information is entered into a mysql database

name
email
ip
comment
value

The value is pregenerated and corresponds to the ID of the review

What I'm scare of is someone who wishes my site "harm" will just press submit over and over and over

What I wish to do is only allow one comment per review from the IP, I believe this can be done by checking to see if An IP already exists in the databse with the same value, and if it does not allowing the user to submit, or simple deleting every entry after the first? how can I achieve this? I'm rather new, and can grasp the basics but this is beyond my abilities

thank you

[Anon]

Hm,
Read ip that last commented in sql base.
if($lastposted=$currectip){
echo"you allready commented";
}
else{
//comment
}

[Anon]

if($lastposted == $currectip){
sorry i made a mistake.