Joomla Jdatabase query code with join does not work - mysql

Question

I run the php code below within the 'Eval' section of a Fabrik form element. The code is supposed to return/put a number in a form field, but nothing appears in the form field.
When I used another query (refer to '$query-> ' lines) the code does work, so I get the impression that the query contains errors; however, when executing the related webpage with the form fields no sql error appears.
I have no idea what is wrong with the query(?)
Code:
$form_productname = 'testproduct';
$form_username = 'myname';
$db = JFactory::getDbo();
// Create a new query object.
$query = $db->getQuery(true);
//$query->select($db->quoteName(array('a.id', 'b.productid')));
$query->select($db->quoteName('b.productid'));
$query->from($db->quoteName('#__products', 'b'));
$query->join('INNER', $db->quoteName('#__extendedreg_users', 'a') . ' ON (' . $db->quoteName('a.user_id') . ' = ' . $db->quoteName('b.owner') . ')
AND (' . $db->quoteName('a.cf_collectivename') . ' = ' . $db->quote($form_username) . ')
AND (' . $db->quoteName('b.productname') . ' = ' . $db->quote($form_productname)).')'.;
//echo $query;exit;
$db->setQuery($query);
$db->execute();
$results = $db->loadObjectList();
return count($results);
UPDATE: cause was syntax php error in where statement:
. $db->quote($form_productname)).
must be:
. $db->quote($form_productname).

Answer 1

You are not getting any errors because you are not catching any errors. Have a look at How to do SQL exception / error handling.
Do at least a $query->dump() and run your query in a console if you can't figure out what is wrong.
I don't understand why are you quoting the value you are comparing $form_username and $form_productname. But maybe it's late and I am tired.