I have a query related question

I have recently purchased a couple of xenforo license and I am looking forward to convert my forums. I have some mods that I am using at vb which are very important to my forum and I or better said my co-admin who knows some php is trying to make them work for xenforo. He is stuck at the query part. In vb is like this

Code:

$query = $vbulletin->db->query_read_slave(" vb query is here "); 
		if ($vbulletin->db->num_rows($query ) ) 
        { 
		the vb code is here;
		}

We have tried the guide here at xenforo but it is not working.

http://xenforo.com/community/threads/mysql-queries-how-to-use-db-in-xenforo-small-notes.5444/

Any help would be much appreciated and we will show out appreciation for your time and help with a donation.

Thank you.

Thank you for your reply. We tried it without success. We used $db->fetchAll and $db->fetchRow for the queries but no joy. Is there anyother function that we should use to query the database?

We did not got any error but it did not work. We tried these queries.

Code:

$query = $db->query("here the query");
			if (XenForo_Application::get('db')->fetchRow($query))
{
	code here
}
        }


$query = $db->fetchAll("here the query");
			if (XenForo_Application::get('db')->fetchRow($query))
{
	code here
}
        }

What we are trying to do is to search all the users tables for the emails and if a user is registered again with the same email he will get a message.

Thank you again. I will pass it along to my other admin that knows a little coding and report back.