PHP登录代码使用mysql数据库出错

Question

我有这个Php代码用于登录检查。但是当它成功匹配用户ID和密码时，就可以了。但是当用户名和密码在数据库中不匹配时，它只是打印：

在isset

并且不打印抱歉。

代码在这里：

<?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.";

?>