Php $\在编辑页面中无法识别GET值

我有一个简单的CRUD，除了更新，所有的东西都已经在工作了，我似乎无法将$u GET值从我的href传递到我的update.php页面。知道我做错了什么吗

更新和删除href的

<td><a href="update.php?updateid=<?php echo $row['stud_id'];?>">Edit</a></td>
<td><a href="index.php?deleteid=<?php echo $row['stud_id'];?>">Delete</a></td>

update.php

<?php
    include 'db.php';


    if(isset($_GET['updateid'])){
        $id = $_GET['updateid'];
    }

    $select = "SELECT * FROM student WHERE stud_id='".$id."'";
    $user = selectStud($select);

    if(isset($_POST['up-submit'])){
        $upfname = $_POST['up-fname'];
        $upmname = $_POST['up-mname'];
        $uplname = $_POST['up-lname'];
        $upcourse = $_POST['up-course'];

        $query = "UPDATE student SET stud_fname='".$upfname."',stud_mname='".$upmname.
        "',stud_lname='".$uplname."',stud_course='".$upcourse."' WHERE stud_id='".$id."'";

        $update = updateStud($query);

        if($update){
            echo "<script>alert('Update Success!'); window.location('index.php');</script>";
        }else{
            echo "<script>alert('Update Failed :('); window.location('index.php');</script>";
        }
    }


?>

<form method="POST" action="update.php">
    <input type="text" name="up-fname" placeholder="First Name" autocomplete="off"><br />
    <input type="text" name="up-mname" placeholder="Middle Name" autocomplete="off"><br />
    <input type="text" name="up-lname" placeholder="Last Name" autocomplete="off"><br />
    <label for="course">Course: </label>
    <select name="up-course">
        <option name="up-course" value="BSIT">BSIT</option>
        <option name="up-course" value="BSHM">BSHM</option>
        <option name="up-course" value="BSED">BSED</option>
        <option name="up-course" value="BSMT">BSMT</option>
    </select><br />

    <input type="submit" name="up-submit" value="Save Changes">
</form>

---

由于在发送POST请求（表单）时无法访问GET参数（URL），因此需要将GET参数嵌入表单中

因此，请在表格中添加以下内容：

<input type="hidden" name="updateid" value="<?php echo $id; ?>>

嘿，有用吗？
<input type="hidden" name="updateid" value="<?php echo $id; ?>>

 if(isset($_POST['up-submit'])){
        $id = $_POST['updateid']; //add this.