在PDO中获取SUM [英] Getting the SUM in PDO

问题描述

下面是我的代码，由于某种原因，它没有给我SUM.总是返回0.为什么不起作用?

Below is my code and for some reason it's not giving me the SUM. This always returns 0. Why doesn't it work?

我已经使用if ($totSubmits==''){来避免数据库中的空白字段.

I've used if ($totSubmits==''){ to avoid blank fields in my database.

我还尝试了删除AS due_fees并使用$dueAmont = $result[0]，但是没有运气.

I also tried removing AS due_fees and using $dueAmont = $result[0], but no luck though.

$sql= "SELECT SUM(dueFees) AS due_fees FROM coursePayments WHERE studentId = $student"; 
$stmt = $c->prepare($sql);
$stmt->execute();
$result = $stmt->fetch(PDO::FETCH_NUM);
$dueAmont = $result['due_fees']; 
if ($dueAmont==""){
    $dueAmont = '0';
}
echo $student." due amount ".$dueAmont;

推荐答案

Gah，请使用参数绑定！另外，对于单行/单列结果， fetchColumn() 很好并且很容易

Gah, use parameter binding! Also, fetchColumn() is nice and easy for single row / single column results

$sql= "SELECT SUM(dueFees) FROM coursePayments WHERE studentId = ?"; 
$stmt = $c->prepare($sql);
$stmt->execute(array($student));
$dueAmont = (int) $stmt->fetchColumn();

附录

在开发时，请始终在完整显示错误的情况下运行PHP环境.这样您就不会错过上面的代码中的简单错误.在php.ini

display_errors = On
error_reporting = E_ALL

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