如何从SQL结果生成“多维关联数组”

// 连接到数据库
$conn = new mysqli("localhost", "username", "password", "database");

// 执行SQL查询
$query = "SELECT customer_id, product_id, SUM(quantity) as total_quantity FROM orders GROUP BY customer_id, product_id";
$result = $conn->query($query);

// 创建多维关联数组
$multi_dimensional_array = array();

// 填充数组
while ($row = $result->fetch_assoc()) {
    $customer_id = $row['customer_id'];
    $product_id = $row['product_id'];
    $total_quantity = $row['total_quantity'];

    // 检查是否存在该客户的键
    if (!isset($multi_dimensional_array[$customer_id])) {
        $multi_dimensional_array[$customer_id] = array();
    }

    // 填充订单数量到相应的位置
    $multi_dimensional_array[$customer_id][$product_id] = $total_quantity;
}

// 使用多维关联数组
foreach ($multi_dimensional_array as $customer_id => $products) {
    echo "Customer ID: " . $customer_id . "<br>";
    foreach ($products as $product_id => $quantity) {
        echo "Product ID: " . $product_id . ", Quantity: " . $quantity . "<br>";
    }
    echo "<br>";
}