If statement problem (PHP)

Hi,

I have tried for hours to get the PHP IF statement logic to work but can't get it to do what I want. Any suggestions?

I want to stop users from registering a username that is already in the database, for some reason, no matter where I put the {} in the If statements (at the end of the code) it either registers any username, won't register any!

$sql2 = "SELECT username FROM `users` WHERE username='$username'";
$result2 = mysql_query($sql2);
if($result2) {
echo "Cannot create username" . mysql_error();
} else {
echo "Username can be created";

$query = "INSERT INTO `users` (username, password, email)
VALUES ('$username', '$password', '$email')";
$result = mysql_query($query);
if(!$result) {
echo "Your query failed. " . mysql_error();
} else {
echo "Welcome " . $username . " You are now registered";
} // end of else
} // end of first else
}
?>