Fail to verify admin permission using function - php

Question

I am makeing a sensitive page that no other user could access without being admin. But when i try to visit that page without being admin it works !
All users are not admin, So they should not be able to access it.
But the page loads fine for them (non admins).
PHP code:
function isAdmin(){
$admin = mysql_query("SELECT `admin` FROM `users` WHERE `username` = '".$_SESSION['username']."'");
if(!($admin)){
echo 'You are not authorised';
return false;
}else{
return true;
}
}
The code on sensitive page:
if(isAdmin()){
$name = $_POST['name'];
$description = $_POST['description'];
$image = $_POST['image'];
$amount = $_POST['amount'];
$sql = "INSERT INTO `store`(`name`, `description`, `price`, `image`) VALUES ('$name','$description','$amount','$image')";
mysql_query($sql);
echo 'Done!';
}
When i post data to this page , it loads and echoes Done! but it should not because:
Current User is not an admin
So, isAdmin() return false
then if(isAdmin()) receives false
So the if statement should not execute.
Yes, I have all these:
Mysql connection
PHP server with correct php.ini
Correct configuration my my users table
The column admin in my Mysql users table is int

Answer 1

You are basing your if condition on whether your query is syntactically correct or not. Since your query is valid, its always going to return something other than false.
use mysqli_num_rows instead.
if(msyql_num_rows($admin)<1)){
echo 'You are not authorised';
return false;
}else{
return true;
}
}

Answer 2

Take count instead of resource value. check below code
function isAdmin(){
$admin = mysql_query("SELECT `admin` FROM `users` WHERE `username` = '".$_SESSION['username']."'");
$count = mysql_num_rows($admin);
if(!($count)){
echo 'You are not authorised';
return false;
}else{
return true;
}
}