PHP编程技巧：如何防止SQL注入攻击

$servername = "localhost";
$username = "your_username";
$password = "your_password";
$dbname = "your_database";

try {
    $conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

    $username = $_POST['username'];
    $password = $_POST['password'];

    $stmt = $conn->prepare("SELECT * FROM users WHERE username = :username AND password = :password");
    $stmt->bindParam(':username', $username);
    $stmt->bindParam(':password', $password);

    $stmt->execute();

    $result = $stmt->fetchAll(PDO::FETCH_ASSOC);
    // 处理查询结果...

} catch (PDOException $e) {
    // 处理异常...
}

$username = $_POST['username'];
$password = $_POST['password'];

if (!empty($username) && !empty($password)) {
    // 过滤和验证用户名和密码
    $filteredUsername = filter_var($username, FILTER_SANITIZE_STRING);
    $filteredPassword = filter_var($password, FILTER_SANITIZE_STRING);

    // 执行查询操作...
} else {
    // 用户名和密码不能为空
    echo "用户名和密码不能为空。";
}