sortierung nach customer fields

$querystr = "
  SELECT * FROM $wpdb->posts
  LEFT JOIN $wpdb->postmeta ON($wpdb->posts.ID = $wpdb->postmeta.post_id)
  LEFT JOIN $wpdb->term_relationships ON($wpdb->posts.ID = $wpdb->term_relationships.object_id)
  LEFT JOIN $wpdb->term_taxonomy ON($wpdb->term_relationships.term_taxonomy_id = $wpdb->term_taxonomy.term_taxonomy_id)
  WHERE $wpdb->term_taxonomy.term_id = 13
  AND $wpdb->term_taxonomy.taxonomy = 'category'
  AND $wpdb->posts.post_status = 'publish'
  AND $wpdb->postmeta.meta_key = 'preis'
  ORDER BY $wpdb->postmeta.meta_value ASC
 ";