public static function getCTAOfSite($nb_site, $nb_site_target_cta)
    {
        $retval = null;

        if (is_numeric($nb_site_id = nb_getMixedValue($nb_site, NABU_SITE_FIELD_ID)) &&
            is_numeric($nb_site_target_cta_id = nb_getMixedValue($nb_site_target_cta, NABU_SITE_TARGET_CTA_FIELD_ID))
        ) {
            $retval = CNabuSiteTargetCTA::buildObjectFromSQL(
                'select stc.* '
                . 'from nb_site s, nb_site_target st, nb_site_target_cta stc '
               . 'where s.nb_site_id=st.nb_site_id '
                 . 'and st.nb_site_target_id=stc.nb_site_target_id '
                 . 'and s.nb_site_id=%site_id$d '
                 . 'and stc.nb_site_target_cta_id=%cta_id$d',
                array(
                    'site_id' => $nb_site_id,
                    'cta_id' => $nb_site_target_cta_id
                )
            );
        }

        return $retval;
    }