i have this code that changes a username, and if it successfully updated, it shows a success message. although when you submit it blank, or if the user already changed their username, and nothing changes in the db, it still shows a success message.

Code:
if(isset($_POST['changeUname'])) {
	if($newUname != "" && $newUname != null) {
		$userID = $_SESSION['testingSiteUserID'];
		$query = "SELECT uname, change_uname FROM members WHERE ID='$userID'";
		$result = mysql_query($query) or die(mysql_error());
		
		if (mysql_num_rows($result) > 0) {
			$row = mysql_fetch_array($result) or die(mysql_error());
			if($row['change_uname'] == 0) {
				mysql_query("UPDATE members SET uname = '$newUname', change_uname = '1' WHERE ID = '$ID'");
			} else {
				$changeUnameErrors[] =  "You cannot change your username.  You have already changed it.";
			}
		}
	} else {
		$changeUnameErrors[] =  "Please enter a valid username!";
	}
	if (mysql_affected_rows() > 0) {
		$unameChanged = true;
	}
}
  
  if($unameChanged == true) {
	 echo "<p><span style='color:red; font-weight:strong; font-size:12px;'>Your account has been successfully updated!</span><p>";
  }