php - 如何让 SUM 可见？

Question

我是 php 和 mysql 的新手，也是这个网站的新手。所以我希望我能做好每一件事。

我正在尝试获取列中某些值的总和。但我在网站上没有看到任何结果。我已经尝试了一个星期，现在搜索了很多信息和主题，但到目前为止还没有任何结果。所以我想请你帮个忙，希望有人能看到我做错了什么。

这就是我现在拥有的。

<?php
$con=mysqli_connect("localhost","user","1234","dbname");
if (mysqli_connect_errno())
{
echo "Failed to connect to MySQL: " . mysqli_connect_error();
}
$res = mysqli_query($con,"SELECT SUM(Bedrag) FROM `Uitdraai` WHERE Datum BETWEEN '2018-01-01' AND '2018-03-01'");
if (FALSE === $res) die("Select sum failed: ".mysqli_error);
$row = mysqli_fetch_row($res);
$sum = $row[0];

mysqli_close($con);
?>

我已经在接下来的页面上尝试了几乎所有选项，但到目前为止还没有运气。我只是得到了我的常规网页，没有答案。

Get sum of MySQL column in PHP

Single Result From SUM With MySQLi

我将非常感激!

Answer 1

SELECT SUM(Bedrag) AS value_sum  FROM `Uitdraai` WHERE Datum BETWEEN '2018-01-01' AND '2018-03-01;

在 PHP 代码中，尝试以下操作:

$con=mysqli_connect("localhost","my_user","my_password","my_db");
// Check connection
if (mysqli_connect_errno())
  {
  echo "Failed to connect to MySQL: " . mysqli_connect_error();
  }
$result = mysqli_query($con,'SELECT SUM(Bedrag) AS value_sum  FROM `Uitdraai` WHERE Datum BETWEEN '2018-01-01' AND '2018-03-01'); 
$row = mysqli_fetch_assoc($result); 
$sum = $row['value_sum'];
echo $sum;

使用 PDO(mysql_query 已弃用)

$stmt = $handler->prepare("SELECT SUM(Bedrag) AS value_sum  FROM `Uitdraai` WHERE Datum BETWEEN '2018-01-01' AND '2018-03-01");
$stmt->execute();

$row = $handler->fetchAll(PDO::FETCH_OBJ);
$sum = $row->value_sum;
echo $sum;