Php MYSQL user authentication

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PHP

I have written a php code to grant access to logged in users with a privilege of "1" to a page and to login if logged in user does not have the access of "1". But when I test, it logs out all users instead

What I have tried:

<?php
session_start();

$conn = mysqli_connect("localhost","root", "","bosmak_properties");

echo $_SESSION['user_name'];

$query=mysqli_query($conn,"SELECT * from users WHERE user_name =".$_SESSION['user_name']);
while ($row=mysqli_fetch_array($query)){
$privileges=$row['privileges'];
}
if($privileges==1){
header ("Location: project_cost.php");
}
else{
	header ("Location: login/logout.php");
}
?>