gistfile1.php

<?php
  $my_query = new WP_Query('category_name=portafolio&showposts=-1&meta_key=show-date');
  $new_order = array();
  while ($my_query->have_posts()) : $my_query->the_post();
    $new_order[strtotime(get('show-date'))] = get_the_id();
  endwhile;
        
  ksort($new_order); // ksort => ASC
  //krsort($new_order); // krsort => DESC
  foreach($new_order as $new){
    $my_query2 = new WP_Query(array('p' => $new));
    while ($my_query2->have_posts()) : $my_query2->the_post();
      the_title();
      echo get('show-date');
      echo "<br />";
    endwhile;
  }
?>