计算来自不同表的多个列php

<?php
// 连接数据库
$servername = "数据库服务器地址";
$username = "用户名";
$password = "密码";
$dbname = "数据库名";

$conn = new mysqli($servername, $username, $password, $dbname);
if ($conn->connect_error) {
    die("连接数据库失败: " . $conn->connect_error);
}

// 编写SQL查询语句
$sql = "SELECT table1.column1, table2.column2 FROM table1 JOIN table2 ON table1.id = table2.id";

// 执行查询
$result = $conn->query($sql);

// 计算列
$total = 0;
if ($result->num_rows > 0) {
    while ($row = $result->fetch_assoc()) {
        $total += $row["column1"] * $row["column2"];
    }
}

// 输出结果
echo "计算结果：" . $total;

// 关闭数据库连接
$conn->close();
?>