正在检查用户是管理员还是正常用户

我在检查数据库中的用户是否为管理员时遇到问题。我这样做了，如果管理员的用户配置文件值为1，那么他们就是管理员，并被重定向到管理员页面，如果不是，他们将被重定向到登录页面。然而，我在数据库中给了我的个人帐户1的值，但它仍然将我重定向到登录页面。

我在下面给出了我的代码，让你看看我是否做错了什么，请告诉我，因为我刚刚开始学习PHP。

<?php 
session_start();
// First we cubrid_execute(conn_identifier, SQL)te our common code to connection to the database and start the session 
require("include/common.php"); 
$admin = $_POST['admin'];
$user = $_POST['username'];
// At the top of the page we check to see whether the user is logged in or not 
if(empty($_SESSION['user'])) 
{ 
    // If they are not, we redirect them to the login page. 
    header("Location: login.php"); 
    // Remember that this die statement is absolutely critical.  Without it, 
    // people can view your members-only content without logging in. 
    die("Redirecting to login.php"); 
} 
// Everything below this point in the file is secured by the login system 
// We can retrieve a list of members from the database using a SELECT query. 
// In this case we do not have a WHERE clause because we want to select all 
// of the rows from the database table. 
$query = " 
    SELECT *
    FROM users 
"; 
try 
{ 
    // These two statements run the query against your database table. 
    $stmt = $db->prepare($query); 
    $stmt->execute(); 
} 
catch(PDOException $ex) 
{ 
    // Note: On a production website, you should not output $ex->getMessage(). 
    // It may provide an attacker with helpful information about your code.  
    die("Failed to run query: " . $ex->getMessage()); 
} 
// Finally, we can retrieve all of the found rows into an array using fetchAll 
$rows = $stmt->fetchAll();
if ($admin == 1) {
    $_SESSION['username'] = $user;
    header("location: memberlist.php");
} 
if ($admin == 0) {
    $_SESSION['username'] = $user;
    header("location: login.php");
}