如何使用PHP实现一个简单的在线订餐系统

<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "dbname";

// 创建连接
$conn = new mysqli($servername, $username, $password, $dbname);

// 检查连接是否成功
if ($conn->connect_error) {
    die("连接失败: " . $conn->connect_error);
}
?>

<?php
// 注册功能
if ($_SERVER["REQUEST_METHOD"] == "POST" && !empty($_POST["username"]) && !empty($_POST["password"])) {
    $username = $_POST["username"];
    $password = $_POST["password"];

    // 将用户名和密码存储到数据库中
    $sql = "INSERT INTO users (username, password) VALUES ('$username', '$password')";
    if ($conn->query($sql) === TRUE) {
        echo "注册成功";
    } else {
        echo "注册失败：" . $conn->error;
    }
}

// 登录功能
if ($_SERVER["REQUEST_METHOD"] == "POST" && !empty($_POST["username"]) && !empty($_POST["password"])) {
    $username = $_POST["username"];
    $password = $_POST["password"];

    // 根据用户名和密码在数据库中进行查询
    $sql = "SELECT * FROM users WHERE username = '$username' AND password = '$password'";
    $result = $conn->query($sql);

    if ($result->num_rows > 0) {
        echo "登录成功";
    } else {
        echo "登录失败";
    }
}
?>

<?php
// 获取菜单信息
$sql = "SELECT * FROM menus";
$result = $conn->query($sql);

// 显示菜单列表
if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        echo "菜名：" . $row["name"]. " - 价格：" . $row["price"]. "<br>";
    }
}

// 处理订单
if ($_SERVER["REQUEST_METHOD"] == "POST" && !empty($_POST["menu_id"]) && !empty($_POST["quantity"])) {
    $menu_id = $_POST["menu_id"];
    $quantity = $_POST["quantity"];
    $user_id = $_SESSION["user_id"];

    // 将订单信息插入到数据库中
    $sql = "INSERT INTO orders (user_id, menu_id, quantity, status) VALUES ('$user_id', '$menu_id', '$quantity', '0')";
    if ($conn->query($sql) === TRUE) {
        echo "下单成功";
    } else {
        echo "下单失败：" . $conn->error;
    }
}
?>