Query builder subquery added multiple quotes if select more than 1 column

Hi,

I use Postgress with Codeigniter V.3.1.10

I try to add subquery like this:

Code:

$this->db->select("pendaftaran_id, pendaftaran_tanggal");
$this->db->join("t_pendaftaran", "t_pendaftaran.pendaftaran_id = t_trx.pendaftaran_id");
$this->db->from("(SELECT trx_no, pendaftaran_id FROM t_transaksi GROUP BY trx_no, pendaftaran_id) as t_trx");
$q = $this->db->get();
return $q->result_array();

and the result is 

Code:

SELECT "pendaftaran_id", "pendaftaran_tanggal" FROM (SELECT trx_no, "pendaftaran_id FROM t_transaksi GROUP BY" "trx_no", pendaftaran_id) as t_trx
JOIN "t_pendaftaran" ON "t_pendaftaran"."pendaftaran_id" = "t_trx"."pendaftaran_id"