在 PDO 中获取 SUM
下面是我的代码，由于某种原因，它没有给我 SUM.这总是返回 0.为什么它不起作用?
Below is my code and for some reason it's not giving me the SUM. This always returns 0. Why doesn't it work?
我使用 if ($totSubmits==''){ 来避免我的数据库中出现空白字段.
I've used if ($totSubmits==''){ to avoid blank fields in my database.
我也尝试删除 AS due_fees 并使用 $dueAmont = $result[0]，但没有运气.
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
哎呀，使用参数绑定！此外，fetchColumn() 对于单行来说非常简单/单列结果
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，始终运行您的 PHP 环境，并显示完整的错误信息.然后你就不会错过上面代码中的简单错误.在 php.ini
display_errors = On
error_reporting = E_ALL
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