title: Mysql use DESC in case statement
body: <p>in below sql command i want to use <code>DESC</code> after <code>WHEN 1 THEN i.id</code> line. i want to if <code>sortable</code> field is <code>1</code> then order by must be have like this command,</p>
  
  <pre><code>ORDER BY i.id DESC
  </code></pre>
  
  <p><strong>Mysql :</strong> </p>
  
  <pre><code>  SELECT 
       SQL_CALC_FOUND_ROWS i.* , 
       c.title AS category_name, 
       u.name, 
       u.family, 
       i.thumb_image,
       CONCAT( u.name, ' ', u.family ) AS author,
       tumbnail_image_width,
       tumbnail_image_height
    FROM   contents i
    JOIN   categories c ON c.id = i.category
    JOIN   users u ON u.id = i.posted_by
    JOIN   settings s ON s.portal = i.portal
    WHERE 
           i.portal = '{$portal_id}'
           AND CASE WHEN post_type = 4
                THEN date(NOW()) BETWEEN i.from_dateTime AND i.to_dateTime 
           ELSE post_type = 1
           END
    AND i.t_status = 1
    ORDER BY
       CASE (SELECT sortable FROM settings)
          WHEN 1 THEN i.id 
          WHEN 2 THEN i.date_time
          WHEN 3 THEN i.order_display
       END                         
    LIMIT {$portalSettings['display_post_count']};";   
  </code></pre>