$username = trim(addslashes(htmlspecialchars($_POST['username'])));
$sql = "SELECT SQL_CACHE * FROM users WHERE username = '$username'";
$result = mysql_query($sql) or die (mysql_error());
$broi = mysql_num_rows($result);
if ($broi >= 1) {
echo "<center>Това потребителско име е заето.</center>";
}