<?php
include 'mysql-connect.php';
$username = $_POST['username'];
$password = $_POST['password'];
$firstname = $_POST['firstname'];
$lastname = $_POST['lastname'];
$age = $_POST['age'];
$ip = $_SERVER['REMOTE_ADDR'];

$result = mysql_num_rows(mysql_query("SELECT * FROM TABLENAME WHERE username='$username'"));
if($result == 1)
        {
        echo "<h1>ERROR!</h1>The username you have chosen already exists!";
        }
else
        {
        mysql_query("INSERT INTO TABLENAME (username, password, firstname, lastname, age, ip)
VALUES ('$username', '$password', '$firstname', '$lastname', '$age', '$ip')");

        echo "
<p>Congratulations! You have successfully registered! </p>
 <p>Click <a href=\"main_login.php\">here</a> to login.</p>";
?>