sql查询到codeigniter活动记录

how do i write this in codeigniter active records?

  MAX(conversations_messages.message_date) > conversations_members.conversation_last_view AS conversation_unread 

I tried this $this->db->select_max('conversations_messages.message_date' > 'conversations_messages.conversation_last_view', 'conversation_unread');

but it said The query you submitted is not valid. Filename: C:\wamp\www\system\database\DB_active_rec.php Line Number: 184

already solved it. these might help someone someday

  MAX(conversations_messages.message_date) > conversations_members.conversation_last_view AS conversation_unread 


 $this->db->select_max('conversations_messages.message_date > conversations_members.conversation_last_view', 'conversation_unread');