如何使$ _POST持久化？

CREATE DATABASE form_data;

USE form_data;

CREATE TABLE form_data (
    id INT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(255) NOT NULL,
    email VARCHAR(255) NOT NULL,
    message TEXT NOT NULL
);

<?php
// 连接到数据库
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "form_data";

$conn = new mysqli($servername, $username, $password, $dbname);

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

// 从表单获取数据
$name = $_POST['name'];
$email = $_POST['email'];
$message = $_POST['message'];

// 将数据插入到数据库
$sql = "INSERT INTO form_data (name, email, message) VALUES ('$name', '$email', '$message')";

if ($conn->query($sql) === TRUE) {
    echo "表单数据已成功保存";
} else {
    echo "Error: " . $sql . "<br>" . $conn->error;
}

$conn->close();
?>