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Try to get the user id like this:

   $user = JFactory::getUser();
   $id= $user->id; 

Try to directly add it onto your sql statement:

$query = $fieldParams->get('query', ''); // Run the query with a having condition because it supports aliases $db->setQuery($query . ' AND created_by =' . $db->q('.$id.' ));

also check permissions and everything.