您只是从db返回结果数组，而不是实际地将最终数量添加到各个行中。你必须这样做：

public function stmt() {
    $this->db->select('customer_id, customer_ref, i_points, group_points, created_on');
    $run_q = $this->db->get('employees');
    if ($run_q->num_rows() > 0) {
        $rows = $run_q->result_array();
        foreach ($rows as $k => $get) {
            $totalpoints = $get['i_points'] + $get['group_points'];
            $percent = 17;
            $amountbycustomer = $totalpoints * 26 * $percent;
            $amountbypref = $this->final($get['customer_id'], $percent);
            $finalamount = $amountbycustomer + $amountbypref;
            $rows[$k]['finalamount'] = $finalamount;
        }
        return $rows;
    }
    return false;
}

或使用参考传递（注意： &get ):

$rows = $run_q->result_array();
    foreach ($run_q->result_array() as &$get) {
        $totalpoints = $get['i_points'] + $get['group_points'];

        $percent = 17;

        $amountbycustomer = $totalpoints * 26 * $percent;

        $amountbypref = $this->final($get['customer_id'], $percent);

        $finalamount = $amountbycustomer + $amountbypref;

        $get['finalamount'] = $finalamount;
    }
    return $rows;