update.php

<?php
include 'config.php';
$id=$_GET['id'];
$result=$link->query("select * from stud where id=$id");
$row=$result->fetch_assoc();

//update when form is sublitted
if(isset($_POST['update'])){
	$name=$_POST['name'];
	$email=$_POST['email'];
	$address=$_POST['address'];
	$link->query("UPDATE stud SET name='$name',email='$email',address='$address' where id=$id");
	header ("location: show.php");
}
?> 

 <h2> update students</h2>
<form method="POST">
	Name:<input type="text" name="name" value="<?=row['name']?>" required><br>
	email:<input type="text" name="email" value="<?=row['email']?>" required><br>
	address:<input type="text" name="address" value="<?=row['address']?>"required> <br>
	<input type="submit" name="update" value="update">
</form>