将timestampdiff与查询构建器codeigniter一起使用

Question

I want to get a time difference from data using the TIMESTAMPDIFF function, but this time i want to use a pure query builder in codeigniter

$this->db->select("TIMESTAMPDIFF(DAY, (".$this->db->select('payment_date')."), (".$this->db->select('download_date').")))",FALSE);
$query = $this->db->get('transaksi');
return $query;

I've tried the code above, but it shows an error like this :

Severity: 4096 Message: Object of class CI_DB_mysqli_driver could not be converted to string

and like this :

You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near '), ())) FROM transaksi ' at line 1

SELECT payment_date, download_date, TIMESTAMPDIFF(DAY, (), ())) FROM transaksi

is there any solution to get the data?

Answer 1

Sub Query not necessary there.

$this->db->select("payment_date, download_date, TIMESTAMPDIFF(DAY, payment_date, download_date)",FALSE);
$query = $this->db->get('transaksi');
return $query->result();

Answer 2

Solution:

 $this->db->select("payment_date, download_date, TIMESTAMPDIFF(DAY, payment_date, download_date)",FALSE);
    $query = $this->db->get('transaksi');
    return $query->result();