代码MySQL中的错误的本地主机 - PHP

Question

我正在使用MySQL在PHP中尝试一个非常简单的代码。 注意：我使用localhost和xampp。

这是我遇到的很多错误之一，有人可以帮我解决我对PHP很新的代码并且似乎无法找到错误。

这是我的代码：

<form method="post">
<input type="email" name="email" id="email" />
<input type="password" name="pass" id="pass" />
<input type="submit" name="submit" id="submit" value="Sign up!" />

<?php

$error = "";
$dbhost = 'localhost';
$username = 'root';
$password = '';
$db = 'users';


if($_POST['submit']) {

    if(!$_POST['email']) $error.="Please enter an email";
        else if (!filter_var($_POST['email'], FILTER_VALIDATE_EMAIL)) $error.="<br />Please enter a valid email address";


    if(!$_POST['pass']) $error.="<br />Please enter a password";
        else{

            if (strlen($_POST['pass']<8)) $error.="<br />Please enter at least 8 characters";
            if (!preg_match('`[A-Z]`', $_POST['pass'])) $error.="<br />Please use at least one capital letter";

        }
    if($error) echo $error;

        else {
        $link = mysql_connect($dbhost,$username,$password, $db);
        $query = "SELECT * FROM `users` WHERE email ='".mysqli_real_escape_string($link, $_POST['email'])."'";

        $result = mysqli_query($link, $query);
        $results = mysqli_num_rows($result);

        if($results) echo "that email address is already registered";

        else {
                $query ="INSERT INTO `users` (`email, `password`) VALUES("'.mysqli_real_escape_string($link, $_POST['email']).'", md5(md5($_POST['email']).$_POST['password'])"')";
                mysqli_query($link, $query);
                echo "You've been signed up!";

        }

    }   
?>