SELECT from subquery in Codeigniter Active Record
I managed to get the query to work by putting the from sub_query into the initial select statement :
$this->db->select("*, (select image_path from image where image_table = 'model' and image_table_id = model_id group by image_table_id limit 1) as ModelImg FROM (SELECT * FROM $view where offer_table = 'derivative' order by offer_order) x");