从 Codeigniter 中的 Active record 获取 SUM 和 group 字段的结果

Question

我需要在 Codeigniter 中构建此查询，但我不知道如何获得 SUM 的结果：

SELECT 
    description, SUM(amount)
FROM
    PAYMENT
WHERE
    (date_payment between '2014-02-01 00:00:00' AND '2014-02-28 23:59:59')
GROUP BY description;

我试图得到这样的结果：

$qwer = $this->db->query("
    SELECT description, SUM(amount)
    FROM PAYMENT
    WHERE (date_payment between '$min_date' AND '$max_date')
    GROUP BY description;");

$i = 0;
foreach ($qwer->result() as $payment) {
    $det_payment[$i] = array(
        'description'=>$payment->description,
        'amount'=>$payment->amount
    );
    $i++;
}

当然 "$payment->amount" 是错误的，但是如果我为 SUM 使用别名，则该模型不起作用。

编辑：现在我可以在描述或总和之间进行选择，但我不能同时使用 select 和 select_sum

$this->db->select('description');
//$this->db->select_sum('amount', 'amount');
$this->db->where('date_payment >=', $min_fecha);
$this->db->where('date_payment <=', $max_fecha);
$this->db->group_by("description");
$qwer = $this->db->get('PAYMENT');

Answer 1

将 FALSE 设置为第二个参数，'select' 允许编写自定义句子。

$this->db->select('description, SUM(amount) AS amount', FALSE);
$this->db->where('date_payment >=', $min_date);
$this->db->where('date_payment <=', $max_date);
$this->db->group_by("description");
$qwer = $this->db->get('PAYMENT');

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