<?php

$Host = Insert Host Name [DB]
$User = Insert User Name [DB]
$Pass = Insert Pass Name [DB]

mysql_connect("$Host", "$User", "$Pass") or die(mysql_error());
mysql_select_db("Logon")

$User = GET_POST('Username');
$Pass = GET_POST('Password');
$Referal = GET_POST('Referal');

$query = mysql_query(SELECT `recruitedfriend` FROM `accounts` WHERE `recruitedfriend` = $referal);
if($query == NULL ){
  echo "The referal already has one friend registered under his name!";
} else {
  mysql_query(INSERT INTO `accounts` WHERE `username, password, recruitedfriend` VALUES $User, $Pass, $Referal)
}

?>