I can't use GET and POST at the same time in PHP

Near the top of my page, I have this:

<?php $id = $_GET['id']; ?>

Then I have some form check conditionals that read from POST:

if (isset($_POST['completeSubmit'])) {
        //code
}

And finally, I have an HTML form which looks like this:

<form action="<?php echo $_SERVER['PHP_SELF']."?id=$id"; ?>" name="complete" method="post">
<input type="submit" id="textButton" name="completeSubmit" value="[mark as complete]">
</form>

The page is initially accessed by using GET with an id variable like this:

http://website.com/page.php?id=1

All subsequent form submissions (which get redirected to the same page) fail. I know you can't send both GET and POST in the same request, but seeing as my form is submitting to $_SERVER['PHP_SELF']."?id=$id" using POST shouldn't it work? This is my first time trying this so it is quite possible I've overlooked something trivial.

Explosion Pills

You can use get and post at the same time, but you shouldn't. If you want to continue to send the ID this is as simple as:

<form ...
   <input type="submit" ...
   <input type="hidden" name="id"
      value="<?php echo htmlspecialchars($_GET['id'], ENT_QUOTES); ?>" />
</form>

Of course you can not use GET and POST methods simultaneously.

However you can use a query string while sending a form using POST method, which being used to populate $_GET array.

To find a certain error you have to provide more info. At least 2 things: