First thing, when you get a blank page, check your error log. Or if you're lazy, add this at the begining of your file to get error messages.
<?php
error_reporting(-1);
ini_set('display_errors', 'On');
?>
It's hard to say, but just looking at your code quickly, I see a problem with your mixup of $_GET
and $_POST
. From what I gather, since your SELECT
works, you send data in $_GET
, and your UPDATE
block is only executed if you have $_POST
data.
Change your html <form method="get">
for <form method="post">
And change your select
block to check if( !empty($_POST['id'])) {