これで:
$this->db->select('count(o.id)');
$this->db->from('orders o');
$this->db->join('order_status_history', 'o.id = order_status_history.order_id');
$this->db->where("(order_status_history.in_dts)::date ='" .$reportDay. "'");
$this->db->where('order_status_history.new_status ' , 6);
order_status_history.new_status が間隔 (2<=order_status_history.new_status<=6) である select count(id) が必要です。単一の整数はありません。このSQLでこれをどのように作成しますか?