Sort on presence of Custom Field, field value, then date

<?php

   // Sort posts in order on presence of a custom field,
   // value of custom field, then date
   $meta_key = 'auteur';  // The meta_key

   // NOTE: The functions and add_filter() calls should go in functions.php
   function mam_posts_fields ($fields) {
      global $mam_global_fields;
      // Make sure there is a leading comma
      if ($mam_global_fields) $fields .= (preg_match('/^(\s+)?,/',$mam_global_fields)) ? $mam_global_fields : ", $mam_global_fields";
      return $fields;
   }
   function mam_posts_join ($join) {
      global $mam_global_join;
      if ($mam_global_join) $join .= " $mam_global_join";
      return $join;
   }
   function mam_posts_where ($where) {
      global $mam_global_where;
      if ($mam_global_where) $where .= " $mam_global_where";
      return $where;
   }
   function mam_posts_orderby ($orderby) {
      global $mam_global_orderby;
      if ($mam_global_orderby) $orderby = $mam_global_orderby;
      return $orderby;
   }
   add_filter('posts_fields','mam_posts_fields');
   add_filter('posts_join','mam_posts_join');
   add_filter('posts_where','mam_posts_where');
   add_filter('posts_orderby','mam_posts_orderby');

   global $wpdb,$wp_query;

   $mam_global_fields = ', IF(ISNULL(pm.meta_id),9,1) as sort_key, pm.meta_value';
   $mam_global_join = " LEFT JOIN $wpdb->postmeta pm ON ($wpdb->posts.ID = pm.post_id AND pm.meta_key = '$meta_key')";
   $mam_global_orderby = "sort_key, pm.meta_value, $wpdb->posts.post_date DESC";
   query_posts('posts_per_page=-1&ignore_sticky_posts=1');
   print_r("REQUEST:$wp_query->request<br />");
   if (have_posts()) {
      while (have_posts()) {
         the_post();
              echo "<p>"; the_title(); echo ' '; the_time('Y-m-d');  echo " $post->sort_key, $post->meta_value</p>";
      }
   }

?>