PHP开发的二手回收网站实现用户账户余额管理

<?php
$db_host = "localhost"; //数据库主机名
$db_user = "root"; //数据库用户名
$db_pass = "123456"; //数据库密码
$db_name = "test"; //数据库名称

//连接数据库
function connect() {
    global $db_host, $db_user, $db_pass, $db_name;
    $conn = mysqli_connect($db_host, $db_user, $db_pass, $db_name);
    if (!$conn) {
        die("数据库连接失败：" . mysqli_connect_error());
    }
    return $conn;
}

//关闭数据库连接
function disconnect($conn) {
    mysqli_close($conn);
}

//执行数据库查询语句
function query($conn, $sql) {
    $result = mysqli_query($conn, $sql);
    if (!$result) {
        die("数据库查询失败：" . mysqli_error($conn));
    }
    return $result;
}

?>

<?php
//充值函数
function recharge($conn, $userId, $amount) {
    //查询原余额
    $sql = "SELECT balance FROM user WHERE id = $userId";
    $result = query($conn, $sql);
    $row = mysqli_fetch_assoc($result);
    $balance = $row['balance'];
    
    //更新余额
    $balance += $amount;
    $sql = "UPDATE user SET balance = $balance WHERE id = $userId";
    query($conn, $sql);
}

//查询余额函数
function getBalance($conn, $userId) {
    $sql = "SELECT balance FROM user WHERE id = $userId";
    $result = query($conn, $sql);
    $row = mysqli_fetch_assoc($result);
    return $row['balance'];
}

//扣除余额函数
function deductBalance($conn, $userId, $amount) {
    //查询原余额
    $sql = "SELECT balance FROM user WHERE id = $userId";
    $result = query($conn, $sql);
    $row = mysqli_fetch_assoc($result);
    $balance = $row['balance'];
    
    //检查余额是否足够
    if ($balance < $amount) {
        die("余额不足");
    }
    
    //更新余额
    $balance -= $amount;
    $sql = "UPDATE user SET balance = $balance WHERE id = $userId";
    query($conn, $sql);
}
?>