пример SubQuery

foreach($_REQUEST["arrFilterO"] as $k=>$val){
      if (is_array($val)){
         foreach($val as $z){
            $arq[]=array(
               "ID" => CIBlockElement::SubQuery("ID", array(
                  "IBLOCK_ID" => $arParams['Other'],
                  "PROPERTY" => array($k=>$z),
               ))
            );
         }
      }else{
         $arq["PROPERTY"][$k]=$val;
      }
   }
   
   $dbElq = CIBlockElement::GetList(array(), array("IBLOCK_ID"=>$arParams['Other'], 'ACTIVE'=>'Y', $arq), false, false, array("ID"));