mySQL help needed - Stopping multiple competition entries

[Empyrion]

Hi,

I'm trying to work out how to stop a user from entering a prize draw more than once. I've got this far:

<?
$user_id = $_COOKIE[user_id_login];
$userquery = mysql_query("SELECT * FROM prize_checkuser WHERE user='$user_id'");
$select_already = mysql_num_rows($userquery);

if($select_already){

echo("Your entry has been received, Thank You!</p>");

}else{

if($_POST['submit']){

//add user id to stop multiple voting
$user_id = $_COOKIE[user_id_login];
$addid = mysql_query("INSERT INTO prize_checkuser (user)". "VALUES ('$user_id')");


$hasvoted = 1;
}

$uri = $_SERVER['REQUEST_URI'];

//display the form!


if($hasvoted==1){

echo("Your vote has been successfully submitted, thanks! <a href=\"prizevote.php\">Click here to return</a><br/>");

}else{
?>

 

[Empyrion]

Sorry, that's gone right over my head. I'm rather new to mySQL!

The user has to be logged in, that's taken care of by a validateuser script.
I've got a data base that should store each user's id number (prize_checkuser) but nothing seems to be being sent to it. From what I understand (I inherited a good part of this code) a variable is created from the user's id number, which is then stored in a mySQL database once the user has entered. If a user tries to enter again, the mySQL database is supposed to check the user's id number to see if it's already stored there and, if it is, use $select_already to stop them voting again.

If that's what you were trying to say, I apologise, but can you pretty much spell it out for me!