如何使用PHP和MySQL设置购物车总价？

<?php
// 连接数据库
$servername = "localhost";
$username = "root";
$password = "password";
$dbname = "cart";

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

// 查询购物车中的产品数据
$sql = "SELECT * FROM products";
$result = $conn->query($sql);

$totalPrice = 0;

if ($result->num_rows > 0) {
    // 遍历购物车中的产品数据
    while($row = $result->fetch_assoc()) {
        $productId = $row["id"];
        $productName = $row["name"];
        $productPrice = $row["price"];
        $productQuantity = $row["quantity"];

        // 计算每个产品的总价并累加到总价变量中
        $productTotalPrice = $productPrice * $productQuantity;
        $totalPrice += $productTotalPrice;

        // 在页面上显示产品信息
        echo "产品ID: " . $productId . "<br>";
        echo "产品名称: " . $productName . "<br>";
        echo "产品价格: " . $productPrice . "<br>";
        echo "产品数量: " . $productQuantity . "<br>";
        echo "产品总价: " . $productTotalPrice . "<br><br>";
    }
} else {
    echo "购物车为空";
}

// 显示购物车的总价
echo "购物车总价: " . $totalPrice;

$conn->close();
?>