php - how to get value which not in table 2 -

how table_1 id not in table_2
table type.
table_1

--------------------------------------------- |  id      |    user                        | --------------------------------------------- |   1      |    jack                        | --------------------------------------------- |   2      |    john                        | --------------------------------------------- 

table_2

------------------------------------------ |  web_id      |    website              | ------------------------------------------ |   2          |   facebook              | ------------------------------------------ |   3          |   google+               | ------------------------------------------ 

i want codeigniter query

$this->db->select("*");         $this->db->from("table_1");         $this->db->where_not_in('id', "table_2.web_id");         return $this->db->get(); 

try

 select id  table_1  id not in  (        select web_id table_2 1  ); 

using codeigniter active records query follows

  $this->db->select('*');   $this->db->where('id not in (select web_id table_2 1)', null, false);   $query = $this->db->get('table_1');