php mysql登录代码

<?php
// 数据库连接配置
$servername = "localhost";
$username = "your_username";
$password = "your_password";
$dbname = "your_database";

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

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

// 获取表单提交的用户名和密码
$username = $_POST['username'];
$password = $_POST['password'];

// 防止SQL注入
$username = $conn->real_escape_string($username);
$password = $conn->real_escape_string($password);

// 查询数据库
$sql = "SELECT * FROM users WHERE username='$username' AND password=MD5('$password')";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    // 输出数据
    while($row = $result->fetch_assoc()) {
        echo "登录成功，欢迎 " . $row["username"] . "!";
    }
} else {
    echo "用户名或密码错误";
}

// 关闭连接
$conn->close();
?>

$stmt = $conn->prepare("SELECT * FROM users WHERE username=? AND password=MD5(?)");
$stmt->bind_param("ss", $username, $password);
$stmt->execute();
$result = $stmt->get_result();

// 假设密码加盐
$salt = "random_salt";
$password = md5($salt . $_POST['password']);

// 查询数据库
$sql = "SELECT * FROM users WHERE username='$username' AND password='$password'";