php mysql插入变量

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

// 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);
}

// 插入数据
$sql = "INSERT INTO users (firstname, lastname, email) VALUES (?, ?, ?)";
$stmt = $conn->prepare($sql);
$stmt->bind_param("sss", $firstname, $lastname, $email);

$firstname = "John";
$lastname = "Doe";
$email = "john@example.com";

$stmt->execute();

echo "新记录插入成功";

$stmt->close();
$conn->close();
?>

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

try {
    $conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
    // 设置 PDO 错误模式为异常
    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

    // 插入数据
    $sql = "INSERT INTO users (firstname, lastname, email) VALUES (:firstname, :lastname, :email)";
    $stmt = $conn->prepare($sql);
    $stmt->bindParam(':firstname', $firstname);
    $stmt->bindParam(':lastname', $lastname);
    $stmt->bindParam(':email', $email);

    $firstname = "John";
    $lastname = "Doe";
    $email = "john@example.com";

    $stmt->execute();

    echo "新记录插入成功";
} catch(PDOException $e) {
    echo "Error: " . $e->getMessage();
}

$conn = null;
?>