如何使用PHP开发微信小程序的团购功能？

<?php
// 连接数据库
$conn = mysqli_connect("localhost", "root", "", "your_database_name");
if (!$conn) {
    die("数据库连接失败: " . mysqli_connect_error());
}

// 获取团购商品列表
$sql = "SELECT * FROM group_buy_goods";
$result = mysqli_query($conn, $sql);

$goodsList = [];
if (mysqli_num_rows($result) > 0) {
    while ($row = mysqli_fetch_assoc($result)) {
        $goodsList[] = $row;
    }
}

// 输出结果
header('Content-Type: application/json');
echo json_encode($goodsList);
?>

<?php
// 连接数据库
$conn = mysqli_connect("localhost", "root", "", "your_database_name");
if (!$conn) {
    die("数据库连接失败: " . mysqli_connect_error());
}

// 获取用户ID和商品ID
$userId = $_POST['userId'];
$goodsId = $_POST['goodsId'];

// 获取商品信息
$sql = "SELECT * FROM group_buy_goods WHERE id = '$goodsId'";
$result = mysqli_query($conn, $sql);
$goods = mysqli_fetch_assoc($result);

if ($goods) {
    // 检查商品库存是否充足
    if ($goods['quantity'] > 0) {
        // 生成订单
        $quantity = 1;
        $total = $goods['price'] * $quantity;

        $sql = "INSERT INTO group_buy_order (goods_id, user_id, quantity, total, created_at) VALUES ('$goodsId', '$userId', '$quantity', '$total', NOW())";
        if (mysqli_query($conn, $sql)) {
            // 更新商品库存
            $sql = "UPDATE group_buy_goods SET quantity = quantity - 1 WHERE id = '$goodsId'";
            mysqli_query($conn, $sql);

            echo "下单成功";
        } else {
            echo "下单失败";
        }
    } else {
        echo "商品库存不足";
    }
} else {
    echo "商品不存在";
}
?>

// 获取团购商品列表
wx.request({
  url: 'https://your_domain/get_goods_list.php',
  success: function(res) {
    var goodsList = res.data;
    console.log(goodsList);
    // 在页面中展示团购商品
  }
});

// 下单
wx.request({
  url: 'https://your_domain/place_order.php',
  method: 'POST',
  data: {
    userId: 'your_user_id',
    goodsId: 'your_goods_id'
  },
  success: function(res) {
    console.log(res.data);
    // 下单成功提示
  }
});