wordpress - Handling URLs correctly with PHP

i have the following case within my plugin for wordpress: I have a details page of a database entry which can be accessed like this:

http://localhost:8888/studio/wp-admin/admin.php?page=myplugin-details&id=42
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The next would be to add sorting options to this page and i solved it with this code:

The url would be:

http://localhost:8888/studio/wp-admin/admin.php?page=myplugin-details&id=42&orderby=answer&order=asc



<?php
      if (!empty($_GET['orderby'])) {
        $pos = strpos($_SERVER["REQUEST_URI"], 'orderby');
        $url = substr($_SERVER["REQUEST_URI"], 0, $pos-1); 
        if ($_GET['order'] == 'desc') {
          echo '<th >';
          echo '<a href="'.$url.'&orderby=answer&amp;order=asc">';
        } else {
          echo '<th >';
          echo '<a href="'.$url.'&orderby=answer&amp;order=desc">';
        }
      } else {
        echo '<th >';
        echo '<a href="'.$_SERVER["REQUEST_URI"].'&orderby=answer&amp;order=asc">';
      }
      ?>
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This works fine, but do i have to do that URL/REQUEST_URI stuff or is there a solution which is much simpler?

Thanks!