Sample Model

function select_all_data() {
    $this->db->select('x.field, v.field, w.field');
    $this->db->from('table1 x');
    $this->db->join('table2 v', 'v.field_id = x.field_id');
    $this->db->join('table3 w', 'x.foreign_id = v.foreign_id');
    $this->db->order_by('x.field_id', 'asc');

    return $this->db->get();
}