php+html+mysql，注册验证手机号是否被注册的时候老是报代码错误，但是我也没写错呀登录页面是可以的

注册成功代码是可以运行的，就是注册验证手机号是否被注册的时候老是报代码错误
这是前端代码：

<body>
<div class="bg">
    <img src="bg_img.jpg" style="width:100%;height:100%;">
    <div class="Forms">
        <div class="Forms_box">
            <div class="Forms_head">
                <a class="a1">快速注册</a>
                <a class="a2 active">快速登录</a>
            </div>
            <div class="submit ">
                <form action="signup.php" method="POST" class="Form1" id="Form1" onsubmit="return check()">
                    <span>账号&nbsp;:&nbsp;</span><input class="input1" type="username" name="signup_userName" onblur="signupusername()" required placeholder="请输入手机号">
                    <p class="text1">手机号码有误</p><p class="text2"></p>
                    <span>密码&nbsp;:&nbsp;</span><input class="input2" type="password" name="signup_passWord" onblur="signuppassword()" required placeholder="请输入密码">
                    <p class="text">密码必须由6-12位数字加字母组成</p>
                    <p class="yz">
                        <span>验证码&nbsp;:</span>
                        <input type ="text" id="text" class="yz_text" required placeholder="请输入验证码">    
                                    <input type="button" id="code" onclick="Code()" title='点击更换验证码' >
                    </p>
                    <input class="sub1" type="submit" value="立即注册">
                </form>
            </div>
            <div class="submit action">
                <form action="login.php" method="POST">
                    <span>账号&nbsp;:&nbsp;</span><input class="input3" type="text" name="login_userName" required placeholder="请输入手机号" >
                    <span>密码&nbsp;:&nbsp;</span><input class="input4" type="password" name="login_passWord" required placeholder="请输入密码">
                    <input class="sub2" type="submit" value="立即登录">
                </form>
            </div>
        </div>
    </div>
</div>
<script src="js/jquery-2.1.1.min.js"></script>
<script src="form.js" charset="utf-8"></script>
</body>

这是php代码，正在这里就是错误：

<?php
$con = mysqli_connect('localhost', 'root', 'root','bdm256727651_db');
if(!$con )
{
    die('连接失败: ' . mysqli_error($con));
}
$signup_userName=$_POST["signup_userName"];

mysqli_select_db($con,'bdm256727651_db');

$username = "select userName FROM forms where userName = '{$signup_userName}' ";
$result = mysqli_query($con,$username );
$rows=mysqli_num_rows($result);

$con->set_charset('UTF-8');

if($rows){
    echo "手机号已注册";
    exit;
}else{
    echo " ";
    exit;
}
mysqli_close($con)
?>

还有一个也是php注册成功代码：

<?php
$con = mysqli_connect('localhost', 'root', 'root','bdm256727651_db');
if(!$con )
{
    die('连接失败: ' . mysqli_error($con));
}

$signup_userName=$_POST["signup_userName"];
$signup_passWord=$_POST["signup_passWord"];

$con->set_charset('UTF-8');
mysqli_select_db($con,'bdm256727651_db');
$sql=" INSERT INTO forms (userName, passWord)
VALUES('{$signup_userName}','{$signup_passWord}') ";
mysqli_query($con,$sql);
echo "<script>window.location.href='signup.html';</script>";    


mysqli_close($con)
?>