php – Mysql在case语句中使用DESC

在下面的sql命令中我想在WHEN 1那么i.id行之后使用DESC.我想如果sortable字段是1那么order by必须有这样的命令,

ORDER BY i.id DESC

MysqL：

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 = '{$portal_iD}'
         AND CASE WHEN post_type = 4
              THEN date(Now()) betweeN i.from_datetiR_585_11845@e AND i.to_datetiR_585_11845@e 
         ELSE post_type = 1
         END
  AND i.t_status = 1
  ORDER BY
     CASE (SELECT sortable FROM setTings)
        WHEN 1 THEN i.id 
        WHEN 2 THEN i.date_time
        WHEN 3 THEN i.order_display
     END                         
  LIMIT {$portalSetTings['display_post_count']};";

SELECT 
     sql_CALC_FOUND_ROWS i.*,tumbnail_image_height,CASE (s.sortablE)
        WHEN 1 THEN 100000000 - i.id 
        WHEN 2 THEN i.date_time
        WHEN 3 THEN i.order_display
     END  AS SortField
  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 = '{$portal_iD}'
         AND CASE WHEN post_type = 4
              THEN date(Now()) betweeN i.from_datetiR_585_11845@e AND i.to_datetiR_585_11845@e 
         ELSE post_type = 1
         END
  AND i.t_status = 1
  ORDER BY SortField                  
  LIMIT {$portalSetTings['display_post_count']};";