Tengo un problema al convertir el código MySQL a una consulta de registro activo de Codeigniter.

SELECT sss.*, c.country_name, c.country_code 
  FROM ( SELECT gr.* 
           FROM (`be_goldrate` as `gr`) 
          WHERE `gr`.`country_id` != 0 
            AND `gr`.`rate_type` = 'calculated' 
           ORDER BY gr.date DESC ) as sss 
   LEFT JOIN `be_countries` as `c` 
     ON `c`.`country_id`=`sss`.`country_id`  
   GROUP BY `sss`.`country_id`

He intentado como se sugiereaquí pero sin éxito.