SQL Injection Test - Login Form

<!DOCTYPE html>
<html><body>

<h1>SQL Injection Test Site</h1>
<h2>Login Form</h2>

<form action="" method="post">
Username: <input type="text" name="username">
Password: <input type="text" name="password">
<input type="submit"></form>

<?php
$db = mysql_connect($host, $user, $pass);
if(!$db){
    die('Could not connect: ' . mysql_error());
}else{
    mysql_select_db($database);
}

if(isset($_POST["username"]) && isset($_POST["password"])){
    $username = $_POST["username"];
    $password = $_POST["password"];
    $result = mysql_query("SELECT id FROM customer_data
                WHERE username = '$username'
                  AND password = '$password'");
    $result = mysql_fetch_assoc($result);
    //we would now process the login if details matched
    echo "Logged in: " . $result['username'];
}
?>

</body></html>