PHP/MySQL User Authentication Not Working

I am using the following code from a book that is explaining how to do database authentication via PHP however I can not get it to work. I continuously get the login prompt and am never allowed into my application. The only thing I modified is the "realm" and field names in order to match up with my database.

Database configuration and connection scripts are external and not included below but I know they are correct as I have no problem inserting or selecting data from my database.

Also, I know mysql is deprecated but I am working on a quick project that will be upgraded once I have time to learn the newer code. Please for now, respond based on mysql in that respect.

Finally this is a very small personal project and I know there are a lot of security errors...that is why I am learning. For now, I am starting with the basics and just trying to get the code to work and then next I plan to learn sessions, encryption, etc.

Please go easy on me :) Thanks

<?php

require_once 'database_connection.php';

if (!isset($_SERVER['PHP_AUTH_USER']) ||
    !isset($_SERVER['PHP_AUTH_PW'])) {
  header('HTTP/1.1 401 Unauthorized');
  header('WWW-Authenticate: Basic realm="The Social Site"');
  exit("You need a valid username and password to be here. " .
       "Move along, nothing to see.");
}

// Look up the user-provided credentials
$query = sprintf("SELECT user_id, username FROM fbo_users" .
    "WHERE username = '%s' AND " .
    "       password = '%s';",
            mysql_real_escape_string(trim($_SERVER['PHP_AUTH_USER'])),
    mysql_real_escape_string(
        crypt(trim($_SERVER['PHP_AUTH_PW']), 
            $_SERVER['PHP_AUTH_USER'])));

$results = mysql_query($query);

if (mysql_num_rows($results) == 1) {
  $result = mysql_fetch_array($results);
  $current_user_id = $result['user_id'];
  $current_username = $result['username'];
} else {
  header('HTTP/1.1 401 Unauthorized');
  header('WWW-Authenticate: Basic realm="FBOtracker"');
  exit("You need a valid username and password to be here. " .
       "Move along, nothing to see.");
}

?>