Codeigniter - select where id not in (another query result)

I'm working into a hotel booking system, currently I'm trying to select available rooms (not reserved). Rooms DB Structure: ID ROOM NAME CAPACITY HOTEL RESERVATIONS DB STRUCTURE: ID CHECK_IN CHECK_OUT ROOMS ... This is my current code: function searchFreeRooms($data){ $check_in = $data['fields']['check_in']; $check_out = $data['fields']['check_out']; $this->db->select("*"); $this->db->from('core_hotel_rooms'); $this->db->where("id NOT IN (select rooms,total_guests from res_hotel where check_in <= '$check_in' AND check_out >= '$check_in' OR check_in <= '$check_out' AND check_out >= '$check_out' OR check_in >= '$check_in' AND check_out <= '$check_out' ) "); $query = $this->db->get(); return $query->result(); } A user can book many rooms in one time, and reserved room id's are stored in column "ROOMS" seperated with commas ex: 2, 3, 5 In my front, room that exist in this column should not be displayed but I'm having trouble because only first id(room) before comma is selected, example: 2,3,5 > only 2 is selected and 3,5 still are displayed in my front. Problem is here: $this->db->where("id NOT IN (select rooms,total_guests from res_hotel where check_in <= '$check_in' AND check_out >= '$check_in' OR check_in <= '$check_out' AND check_out >= '$check_out' OR check_in >= '$check_in' AND check_out <= '$check_out' ) "); I tried this: $this->db->where("id NOT IN (1, 2) "); and it works perfectly but not upper method with second query. Sorry for my english... Many thanks to all those who can help!