使用SQL检查数据库中是否存在用户

我试图检查一个名为members的表，看看是否存在一个用户的电子邮件和密码。我能够连接到数据库，但由于某种原因，它跳所有这些if语句和回声'You have been logged in!'，即使我把错误的电子邮件或密码?下面是html和php:

<form action="/login-user" method="POST">
    Email: <input type="text" name="login_email"><br>
    Password: <input type="password" name="login_password"><br>
    <button type="submit">Login</button>
</form>

<?php
    session_start();
    /*error_reporting(0);*/
    require 'users/functions/user-functions.php';
    require 'users/connect-database.php';
    if (empty($_POST) === false) {
        $email = mysqli_real_escape_string($connection, $_POST['login_email']);
        $password = stripslashes(mysqli_real_escape_string($connection, $_POST['login_password']));
        $encrypted_password = md5($password);
        if (empty($email)) {
            echo 'You need to enter an email<br>';
        } else if (empty($password)) {
            echo 'You need to enter a password<br>';
        } else if(user_exists($connection, $email, $encrypted_password) === false) {
            echo 'You don''t seem to be registered?';
        } else if (user_active($connection, $email, $encrypted_password) === false) {
            echo 'You haven''t activated your account!';
        } else {
            $login = login($connection, $email, $encrypted_password);
            if ($login === false) {
                echo 'That email/password combination is incorrect';
            } else {
                $_SESSION['user_id'] = $login;
                $_SESSION['logged_in'] = true;
                echo 'You have been logged in!';
            }
        }
    /*print_r($errors);*/
} else {
    echo 'inputs were empty<br>';
}
require 'users/disconnect-database.php';
?>

'user-functions.php'文件内容:

<?php
    function sanitize($connection, $data) {
        return mysqli_real_escape_string($connection, $data);
    }
    function logged_in() {
        return $_SESSION['logged_in'];
    }
    function user_exists($connection, $email, $password) {
        $query = mysqli_num_rows(mysqli_query($connection, "SELECT * FROM members WHERE email = '$email' AND password = '$password'"));
        return ($query > 0) ? true : false;
    }
    function user_active($connection, $email, $password) {
        $query = mysqli_query($connection, "SELECT user_id FROM members WHERE email = '$email' AND password = '$password' AND `active` = 1");
        return ($query !== false) ? true : false;
    }
    function return_user_id($connection, $email, $password) {
        return mysqli_query($connection, "SELECT user_id FROM members WHERE email = '$email' AND password = '$password'");
}
    function login($connection, $email, $password) {
        /*$user_id = mysql_result(mysqli_query($connection, "SELECT user_id FROM members WHERE email = '$email' AND password = '$password'"), 0, 'user_id');*/
        /*$password = md5($password);*/
        $query = mysqli_query($connection, "SELECT user_id FROM members WHERE email = '$email' AND password = '$password'");
        /*return (mysqli_query($connection, $query) or die (false));*/
        if ($query === false) {
            return false;
        } else {
            return $query;
        }
    /*return ($query !== false) ? true : false;*/
    }
    function log_out() {
        unset($_SESSION['logged_in']);
        session_unset();         
        session_destroy();
    }
?>

如果答案是使用mysql_result或mysqli_result，请详细解释，因为即使阅读了手册和W3Schools以及其他地方，我仍然不明白这些功能是如何工作的。

谢谢你的回答，顺便说一下，我 have 读了所有关于这个东西的帖子，但我没有找到任何答案。谢谢。