Error in PHP Login Code using mysql database

Question

I have this Php Code for login checking. But When It succeesfully matches userid and password, it is OK. But when user name and password does not match in database, then it is only printing:

In isset

and Not printing sorry.

Code is here:

<?php
define('DB_HOST', 'mysql.hostinger.in');
define('DB_NAME', 'u157309623_p2');
define('DB_USER', 'u157309623_p2');
define('DB_PASSWORD','nielit');

$db=@mysqli_connect(DB_HOST,DB_USER,DB_PASSWORD,DB_NAME) or die("Failed to connect to MySQL: " . mysqli_error($db));

/*
$ID = $_POST['user'];
$Password = $_POST['pass'];
*/
function SignIn(mysqli $db)
{
session_start();   //starting the session for user profile page

    $query = mysqli_query($db,"SELECT *  FROM UserName where userName = '$_POST[user]' AND pass = '$_POST[pass]'") or die(mysqli_error($db));
    $row = mysqli_fetch_array($query) or die(mysqli_error($db));
    if(!$row)
    {

        echo "SORRY";

    }
    else
    {
                echo "SUCCESSFULLY LOGIN";

    }

echo "Not in Loop.";

}
if(isset($_POST['submit']))
{
echo "in isset.";
    SignIn($db);
}
echo "Last Line.";

?>