$user = JFactory::getUser();

$db = JFactory::getDbo();
$query = $db->getQuery(true);
$query->select($db->quoteName(array('i.pagamento', 'i.pagata')));
$query->from($db->quoteName('#__iscrizione', 'i'));
$query->join('INNER', $db->quoteName('#__socio', 's') . ' ON (' . $db->quoteName('i.parent_id') . ' = ' . $db->quoteName('s.id') . ')');
$query->where($db->quoteName('s.user_id') . ' = '.$user->id );
$db->setQuery($query);
$column = $db->loadRow();