如何用简单的PHP在同一页面发帖？

我正在尝试仅使用 PHP 创建一个注册系统。这就是一个例子。但我想我做错了什么。我试图在 StackOverFlow 帖子中找到类似的解决方案，但没有得到任何确切的解决方案。如果有人能帮助我找到下面代码中的错误，那就太好了。

<?php
// POST HANDLER -->

if(isset($_POST['registerForm']))
{
    conFunc(); // Connection Function

    $userid = $_POST['userid'];
    $name = $_POST['name'];

    $getUserId = mysql_query("SELECT * FROM `user` WHERE `userid` = '".$userid."'");
    $id = mysql_fetch_array($getUserId);

    if($id)
    {
        echo "This User ID is Already Available on the System, Please Choose Something Else!";
    }
    else
    {

        $query = mysql_query("INSERT INTO `user` (`userid`, `name`");

        if($query)
        {
            echo "A New User is Registered Successfully:<br /><br />";
            echo "<b>User ID:</b> " . $userid . "<br />";
            echo "<b>User Name:</b> " . $name . "<br />";
        }
        else
        {
            echo "There is an Error while Saving: " . mysql_error();
            echo "<br />Please click on Create User from menu, and try again<br /><br />.";
        }

    }
    exit;
}
// POST HANDLER -->
?>

<!-- FORM GOES BELOW -->

<form action="<?php echo $_SERVER['PHP_SELF']?>" method="post" name="registerForm">

<table style="width: 100%">
    <tr>
        <td>User ID</td>
        <td><input name="userid" type="text" style="width: 300px" /><br /></td>
    </tr>
    <tr>
        <td>Name</td>
        <td><input name="name" type="text" style="width: 300px" /><br /></td>
    </tr>
    <tr>
        <td></td>
        <td><input style="width: 130px; height: 30px" type="submit" name="submit" value="Register Now" /><br /></td>
    </tr>
</table>

</form>

您必须检查提交按钮是否设置。

if(isset($_POST['registerForm']))

应该

if(isset($_POST['submit'])) {
    // your php code
} else {
    // your html code

}