Get started quickly: Develop a simple yet powerful shopping mall coupon with PHP

CREATE TABLE users (
  user_id INT PRIMARY KEY AUTO_INCREMENT,
  username VARCHAR(50) NOT NULL,
  password VARCHAR(50) NOT NULL,
  balance DECIMAL(10, 2) DEFAULT 0
);

CREATE TABLE coupons (
  coupon_id INT PRIMARY KEY AUTO_INCREMENT,
  coupon_code VARCHAR(50) NOT NULL,
  discount DECIMAL(10, 2) NOT NULL,
  threshold DECIMAL(10, 2) DEFAULT 0,
  start_time DATETIME,
  end_time DATETIME,
  is_used TINYINT(1) DEFAULT 0
);

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

$conn = mysqli_connect($servername, $username, $password, $dbname);

if (!$conn) {
    die("连接数据库失败: " . mysqli_connect_error());
}
?>

<?php
if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    $username = $_POST['username'];
    $password = $_POST['password'];

    $sql = "INSERT INTO users (username, password) VALUES ('$username', '$password')";

    if (mysqli_query($conn, $sql)) {
        echo "注册成功！";
    } else {
        echo "注册失败：" . mysqli_error($conn);
    }
}
?>
<h1>用户注册</h1>
<form method="POST">
    <input type="text" name="username" placeholder="用户名" required>
    <input type="password" name="password" placeholder="密码" required>
    <button type="submit">注册</button>
</form>

<?php
session_start();

if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    $username = $_POST['username'];
    $password = $_POST['password'];

    $sql = "SELECT * FROM users WHERE username='$username' AND password='$password'";
    $result = mysqli_query($conn, $sql);

    if (mysqli_num_rows($result) == 1) {
        $_SESSION['username'] = $username;
        echo "登录成功！";
    } else {
        echo "用户名或密码错误！";
    }
}
?>
<h1>用户登录</h1>
<form method="POST">
    <input type="text" name="username" placeholder="用户名" required>
    <input type="password" name="password" placeholder="密码" required>
    <button type="submit">登录</button>
</form>

<?php
session_start();

if (!isset($_SESSION['username'])) {
    header("Location: login.php");
    exit;
}

$username = $_SESSION['username'];

if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    $coupon_code = $_POST['coupon_code'];

    $sql = "SELECT * FROM coupons WHERE coupon_code='$coupon_code' AND is_used=0";
    $result = mysqli_query($conn, $sql);

    if (mysqli_num_rows($result) == 1) {
        $coupon = mysqli_fetch_assoc($result);
        $discount = $coupon['discount'];
        $threshold = $coupon['threshold'];
        $balance = mysqli_fetch_assoc(mysqli_query($conn, "SELECT balance FROM users WHERE username='$username'"))['balance'];

        if ($balance >= $threshold) {
            $new_balance = $balance - $discount;
            mysqli_query($conn, "UPDATE users SET balance=$new_balance WHERE username='$username'");
            mysqli_query($conn, "UPDATE coupons SET is_used=1 WHERE coupon_code='$coupon_code'");

            echo "使用优惠券成功！";
        } else {
            echo "账户余额不足，请先充值！";
        }
    } else {
        echo "优惠券已被使用或不存在！";
    }
}

$sql = "SELECT * FROM coupons WHERE is_used=0";
$result = mysqli_query($conn, $sql);
$coupons = mysqli_fetch_all($result, MYSQLI_ASSOC);
?>
<h1>领取优惠券</h1>
<?php foreach ($coupons as $coupon) { ?>
    <form method="POST">
        <input type="hidden" name="coupon_code" value="<?php echo $coupon['coupon_code']; ?>">
        <h3><?php echo $coupon['coupon_code']; ?></h3>
        <p>折扣金额：<?php echo $coupon['discount']; ?></p>
        <p>使用门槛：<?php echo $coupon['threshold']; ?></p>
        <button type="submit">领取</button>
    </form>
<?php } ?>