PHP Friend add system doesn't work properly

hope you can help me out here, i have tryed all day figuring this one out.

I have a friend system and some users, they can add each other and that works perfectly, but the problem is they can add each other more then once..

heres my script that checks if they already are friends..

but it doesnt work :(

<?
// connect Databasen
include('connect.php');
//hvis get bruger ikke er tom
if (!empty($_GET["bruger"])) {
//tjeker om venner er anøsgt i forvejen
$bruger = $_SESSION['username'];
开发者_StackOverflow$ven = $_GET["bruger"];
$tjek = mysql_query("SELECT * FROM venner WHERE username='$bruger' AND ven='$ven'");
if ($tjek) {
//indsæt
mysql_query("INSERT INTO venner VALUES('','$bruger','$ven','','nej')");
echo "venskab er ansøgt";
exit;
}
else {
echo "Du har allerede ansøgt";
}
}
?>

The easiest solution is to create a unique index on venner:

CREATE UNIQUE INDEX akVenner (username, ven) ON venner;

You should use:

if (mysql_num_rows($tjek) == 0) {
    INSERT SOMETHING
} else {
    DOING SOMETHING
}

Don't forget using escaping input data for avoiding sql-injection.

You need to find the relationship of the two forms, regardless of who created it:

$tjek = mysql_query("SELECT * FROM venner 
    WHERE (username='$bruger' AND ven='$ven') OR 
    (username='$ven' AND ven='$bruger')");

if (mysql_num_rows($tjek)==0) {