SUM 函数在 SQL 查询中产生错误

Question

我正在尝试通过 php 脚本获取有关 SQL 表的信息，但是，每当我添加 SUM 函数时，我都会收到以下错误“注意：尝试获取非对象的属性 'num_rows'”

我不知道发生了什么，但如果有人能解释/指出我如何解决这个问题的正确方向，我将不胜感激

这是“损坏的”代码

<?php
require("connect.php");
$inNo = $_POST["inNo"];
$sql = "SELECT invoice.invoice_no, invoice.date, invoice.cust_id, invoice.emp_id, invoice_line.prod_id, 
               invoice_line.qty, product.cost_price, (product.cost_price * invoice_line.qty) AS `multi`, 
               customer.first_name AS `customer_fname`, customer.last_name AS `customer_lname`, 
               employee.first_name AS `emp_fname`, employee.last_name AS `emp_lname`, 
               product.name AS `proname` 
        FROM invoice INNER JOIN invoice_line ON invoice.invoice_no = invoice_line.invoice_no 
                     INNER JOIN product ON invoice_line.prod_id = product.id 
                     INNER JOIN customer ON invoice.cust_id = customer.id 
                     INNER JOIN employee ON invoice.emp_id = employee.id, SUM(multi) AS `invoicetotal` 
        WHERE cust_id = '" . $inNo . "'";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    //open table
    echo '<table class="table table-striped" id="outTable">';
    echo "<tr><th>Product</th><th>Qty</th><th>Price</th><th>Total cost</th></tr>";
    // output data of each row
    $ctr = 0;
    while($row = $result->fetch_assoc()) {
        if ($ctr == 0)
        {
            echo "<h1>Invoice Number: " . $row["invoice_no"]. "</h1>";
            echo "<p>Customer: " . $row["customer_fname"]. " " . $row["customer_lname"]."</p>";
            echo "<p>Employee: " . $row["emp_fname"]. " " . $row["emp_lname"]. "</p>";
            echo "<p>Date: " . $row["date"]. "</p>";
        }
        echo "
        <tr>
        <td>" . $row["proname"]. "</td>
        <td>" . $row["qty"]. "</td>
        <td>" . $row["cost_price"]. "</td>
        <td>" . $row["multi"]. "</td>
        </tr>";
        $ctr++;
    }
} else {
    echo "0 results";
}
$conn->close();
?>

Answer 1

您需要在 FROM 上方的 SELECT 部分中插入 SUM()：

SELECT 
 invoice.invoice_no, 
 invoice.date, 
 invoice.cust_id, 
 invoice.emp_id, 
 invoice_line.prod_id, 
 invoice_line.qty, 
 product.cost_price, 
 (product.cost_price * invoice_line.qty) AS `multi`, 
 customer.first_name AS `customer_fname`, 
 customer.last_name AS `customer_lname`, 
 employee.first_name AS `emp_fname`, 
 employee.last_name AS `emp_lname`, 
 product.name AS `proname`,
 SUM(multi) AS `invoicetotal` 
FROM invoice 
INNER JOIN invoice_line 
  ON invoice.invoice_no = invoice_line.invoice_no 
INNER JOIN product 
  ON invoice_line.prod_id = product.id 
INNER JOIN customer 
  ON invoice.cust_id = customer.id 
INNER JOIN employee 
  ON invoice.emp_id = employee.id` WHERE cust_id = 99

顺便说一句，格式化代码是明智的 - SQL 代码也是 - 很好。