$username = htmlspecialchars($_POST['username']);
$password = htmlspecialchars($_POST['password']);

$sql = "SELECT * FROM `db_user` WHERE Username='$username' AND Password='$password'";
$query = mysqli_query($db_handle, $sql) or die ("Error in query: " . mysqli_error($db_handle));

$user_row = mysqli_fetch_assoc($query);

mysqli_close($db_handle);


$smarty->assign("DATA", $user_row);
$smarty->assign("USERNAME", $username);
$smarty->assign("PASSWORD", $password);
$smarty->caching=0;
$smarty->display('sign_in.tpl');

{if $DATA.Username eq $USERNAME and $DATA.Password eq $PASSWORD}

GOOD

{else}

Bad

{/if}

Smarty_Variable Object (3)
->value = Array (10)
  ID => "14"
  Username => "myuser"
  Password => "mypass"
  Name => "me"
  Email => "an email"
  Country => "Russia"
  Activation => "1"
->nocache = false
->scope = "file:sign_in.tpl"