Selecting values from MySQL with PHP

So I have a php file called extract_values.php .
In it I have the next codes :

<?php
require_once('config.php');

$requestSQL = 'SELECT * FROM database WHERE username=$user';
$result = mysql_query($requestSQL);
while ($rand = mysql_fetch_array($result)) {
echo $rand['specificrow'];
}
?>

Code (markup):

Now here's the catch , I want $user to be setted from outside , something like this :

$user = $_GET['user'];

Code (markup):

and ofcourse , I will set the user from the url :

website.com/extract_values.php?user=batman

Code (markup):

so that the php will extract FROM database WHERE username=batman .

So what's the problem ? I don't know ( well .. it doesn't work ) how to format the $user in that php code to select from Mysql .
The next code doesn't work :

$requestSQL = 'SELECT * FROM database WHERE username=$user';

Code (markup):

it could be because I need something like .$name. or what ?

 

$requestSQL = "select * from database where username = '" . mysql_real_escape_string($_GET['user']) . "'";

 

$requestSQL = "SELECT * FROM database WHERE username='$user'";

PHP:

 

Thanks ! It worked with SmallPotatoes code
@ActiveFrost : I think I tryed that one but it didn't work ... thank you also.

 

What I wrote is exactly how PHP/MySQL works ! It can't fail ( in case if it does, your server is too old to handle it ).

 

ActiveFrost: You didn't guard the string literal in the query ($user) against special characters. Will fail with some values of $user, and also it's bad security practice.