jQuery 验证器插件 - 检查 mysql 数据库中现有的用户名/电子邮件

我已经成功创建了一个表单，该表单将用户提交并添加到 mysql 数据库中，并且使用"jQuery Validator"插件进行表单验证适用于除检查用户名是否已存在于数据库之外的所有内容......

我刚刚花了大约 8 个小时阅读并试图找出一种使用"jQuery Validator"插件定义新方法的方法。我似乎不明白我将如何检查数据库中输入的用户名或电子邮件，并使用jQuery返回它是否已经存在。

我的代码：

<script src="../assets/js/main.js"></script>
<script src="../assets/js/ajax.js"></script>
<script src="http://ajax.aspnetcdn.com/ajax/jquery.validate/1.11.0/jquery.validate.min.js"></script>
<!-- FORM VALIDATION -->
<script type="text/javascript">

    jQuery.validator.addMethod("checkExists", 
function(value, element) {
    //No idea what to call here
}, 
"Username already exists."
);

        //<![CDATA[
        $(window).load(function(){
        $("form").validate({
        rules: {
            username: {minlength: 3, required: true, checkExists: true},
            email: {email: true, required: true},
            pass1: {minlength: 3, required: true},
            pass2: {minlength: 3, required: true, equalTo: "#pass1"},
            country: {required: true},
            tandc: {required: true},
        },
        messages: {
        username:   {required: "You need to enter a Username."},
        email:      {required: "You need to enter an Email Address."},
        pass1:      {required: "You need to enter a Password."},
        pass2:      {required: "You need to enter your password again.", equalTo: "Your passwords don't match."},
        country:    {required: "You need to tell us where you live."},
        tandc:      {required: "You need to read and agree to the Terms and Conditions to use CGE."}
        },

        showErrors: function(errorMap, errorList) {
        $.each(this.successList, function(index, value) {
        return $(value).popover("hide");
        });
        return $.each(errorList, function(index, value) {
        var _popover;
        console.log(value.message);
        _popover = $(value.element).popover({
        trigger: "manual",
        placement: "right",
        content: value.message,
        template: "<div class='"popover'"><div class='"arrow'"></div><div class='"popover-inner'"><div class='"popover-content'"><p></p></div></div></div>"
        });
        _popover.data("popover").options.content = value.message;
        return $(value.element).popover("show");
        });
        }
        });
        });//]]>
</script>

如果有人聪明人可以修改我的代码来告诉我应该如何做，这将是一个很大的帮助 - 我觉得我快要疯了！

提前感谢，迫不及待地想看到解决方案：-）

编辑 - 这是我当前的代码

似乎什么都没有发生，我觉得我更接近了：

当前代码：

注册.php

    $(window).load(function(){
            $("form").validate({
            rules: {
                username: {minlength: 3, required: true},
                email: {email: true, required: true, remote: {url: "./validation/checkUnameEmail.php", type : "post"}},
                pass1: {minlength: 3, required: true},
                pass2: {minlength: 3, required: true, equalTo: "#pass1"},
                country: {required: true},
                tandc: {required: true}
},

检查Uname电子邮件.php

<?php
    include_once(".../php_includes/db_conx.php");
    $email = urldecode($_POST['email']);
    $result = mysqli_query($db_conx, "SELECT * FROM users WHERE email = '$email' LIMIT 1;");
    $num = mysqli_num_rows($result);
    if($num == 0){
        echo "true";
    } else {
        echo "E-Mail-Adresse schon registriert.";
    }
    mysqli_close($db_conx);
?>

*db_conx.php*

<?php
$db_conx = mysqli_connect("localhost", "root", "root", "membership");
//Evlauate the connection
if (mysqli_connect_errno()){
    echo mysqli_connect_error();
    exit();
}
?>