php代码如何加后台

<code class="php">$servername = "localhost";
$username = "root";
$password = "";
$dbname = "test_db";

// 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);
}</code>

<code class="php">$sql = "CREATE TABLE users (
  id INT(6) UNSIGNED AUTO_INCREMENT PRIMARY KEY,
  username VARCHAR(30) NOT NULL,
  password VARCHAR(255) NOT NULL
)";

// 执行查询
if ($conn->query($sql) === TRUE) {
  echo "数据表创建成功";
} else {
  echo "数据表创建失败: " . $conn->error;
}</code>

<code class="php">$username = "admin";
$password = "password";

$sql = "INSERT INTO users (username, password)
VALUES ('$username', '$password')";

// 执行查询
if ($conn->query($sql) === TRUE) {
  echo "数据插入成功";
} else {
  echo "数据插入失败: " . $conn->error;
}</code>

<code class="php">// 开启会话
session_start();

// 检查用户是否已登录
if (!isset($_SESSION['username'])) {
  header("Location: login.php");
  exit;
}

// 获取用户输入
$username = $_POST['username'];
$password = $_POST['password'];

// 验证用户凭证
$sql = "SELECT * FROM users WHERE username='$username' AND password='$password'";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
  // 登录成功
  $_SESSION['username'] = $username;
  header("Location: dashboard.php");
  exit;
} else {
  // 登录失败
  echo "登录失败";
}</code>

<code class="php">// 开启会话
session_start();

// 检查用户是否已登录
if (!isset($_SESSION['username'])) {
  header("Location: login.php");
  exit;
}

// 显示仪表盘内容
echo "欢迎 " . $_SESSION['username'] . "！";
echo "<br>";
echo "这是您的仪表盘";</code>

<code class="php">// 开启会话
session_start();

// 注销用户并销毁会话
session_destroy();

// 重定向到登录页面
header("Location: login.php");
exit;</code>