我正在創建一個帶有單個 index.php 文件的網站，其中包含 2 個標頭。我正在使用“include”語句來在索引上調用標頭?！癶eader1.php”是網站訪客的默認標頭，其中還包含“登錄”按鈕。而“header2.php”是那些已登錄其帳戶并具有“注銷”按鈕的標題。問題是，當訪客訪問網站時，網站將顯示默認標頭“header1.php”。當用戶登錄他/她的帳戶時，將顯示“header2.php”。我應該如何調用標題？if else 語句中應該寫什么條件？它可能需要訪問 MySQL 數據庫來獲取用戶數據。例子：<?phpif( user log in to his account ){    include 'header2.php';}else{    include 'header1.php';}我的登錄腳本是：<?phpsession_start();$username = $_POST['username'];$password = $_POST['password'];$connect = mysqli_connect("localhost", "root", "", "yfcgk_canlaon");$query = mysqli_query($connect, "SELECT * from members WHERE USERNAME = '$username' and PASSWORD = '$password'");$count = mysqli_num_rows($query);if($count <= 0 ){    session_start();    header("location:index.php?error");}else{    $_SESSION['user'] = 1;    $_SESSION['username'] = ucwords($username);    header("location:index.php");}?>