防sql注入代码 php

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

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

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

    // 执行查询
    $stmt->execute();

    // 获取结果
    $result = $stmt->fetchAll(PDO::FETCH_ASSOC);
    print_r($result);
} catch (PDOException $e) {
    echo "Error: " . $e->getMessage();
}
$conn = null;
?>

<?php
$username = $_POST['username'];
$password = $_POST['password'];

// 简单的输入验证
if (!preg_match('/^[a-zA-Z0-9_]+$/', $username)) {
    die("Invalid username");
}

// 连接数据库并执行查询（使用预处理语句）
?>

CREATE USER 'webappuser'@'localhost' IDENTIFIED BY 'password';
GRANT SELECT, INSERT, UPDATE ON myDB.* TO 'webappuser'@'localhost';