Php 我的表名为；费用“；及；订单“；我想分别计算总数，然后从费用中减去订单总数

通过此查询获得的订单表总计：

<?php $res = mysqli_query($conn,'SELECT sum(totalprice) FROM orders');
if (FALSE === $res) die("Select sum failed: ".mysqli_error);
$row = mysqli_fetch_row($res);
$sum = $row[0];
echo $sum;?>

<?php $res = mysqli_query($conn,'SELECT sum(amount) FROM expenses');
if (FALSE === $res) die("Select sum failed: ".mysqli_error);
$row = mysqli_fetch_row($res);
$sum = $row[0];
echo $sum;?>

通过此查询获得的费用表总计：

<?php $res = mysqli_query($conn,'SELECT sum(totalprice) FROM orders');
if (FALSE === $res) die("Select sum failed: ".mysqli_error);
$row = mysqli_fetch_row($res);
$sum = $row[0];
echo $sum;?>

<?php $res = mysqli_query($conn,'SELECT sum(amount) FROM expenses');
if (FALSE === $res) die("Select sum failed: ".mysqli_error);
$row = mysqli_fetch_row($res);
$sum = $row[0];
echo $sum;?>

现在我想从订单和费用表中减去总数。

---

示例订单总额-费用总额

如果您提到的sript工作正常，您可以执行以下操作：

$resOrder = mysqli_query($conn,'SELECT sum(totalprice) FROM orders');
if (FALSE === $resOrder) die("Select sum failed: ".mysqli_error);
$row = mysqli_fetch_row($resOrder);
$total = $row[0];
echo $orderTotal;

$resExp = mysqli_query($conn,'SELECT sum(amount) FROM expenses');
if (FALSE === $resExp) die("Select sum failed: ".mysqli_error);
$row = mysqli_fetch_row($resExp);
$expensesTotal = $row[0];
echo $expensesTotal ;

现在，要获得结果，只需执行以下操作：

echo $result = $expensesTotal - $orderTotal; 

---

如果您有任何问题，请告诉我。

您离我们太近了。您只需要为总值指定不同的变量名

<?php 
    $orderRes = mysqli_query($conn,'SELECT sum(totalprice) as orders_total FROM orders');   //Aliases are a beautiful thing to use. In this case I am giving the sum of orders an alias - orders_total
    $row = mysqli_fetch_assoc($orderRes);
    $ordersTotal = $row['orders_total'];

    $res = mysqli_query($conn,'SELECT sum(amount) as expenses_total FROM expenses');
    $row = mysqli_fetch_assoc($res);
    $expensesTotal = $row['expenses_total']

    $diff = $ordersTotal - $expensesTotal;    //Simply substract expensesTotal from ordersTotal
    echo $diff; ?>

您遇到了什么麻烦？您只需要使用不同的变量名，并将它们放在同一个脚本中。是的，它可以工作，唯一的问题是变量“$total”的名称是echo作为“$orderTotal”，谢谢您的帮助