SELECT id,wp.title,barcode FROM ПИШЕТЕ НАЗВАНИЕ ТАБЛИЦЫ(КОТОРУЮ СКОПИРОВАЛИ) wp WHERE wp.weight IN ('',0, ' ') OR wp.weight IS null

SELECT id,wp.title,barcode FROM apgr_product wp WHERE wp.weight IN ('',0, ' ') OR wp.weight IS null

<?php
require('setup.inc.php');

$list = \RS\ORM\Request::make()
   ->select('id, title, barcode')
   ->from(new \Catalog\Model\Orm\Product())
   ->where("weight IN ('',0, ' ') OR weight IS null")->exec()
   ->fetchSelected(null);

echo "
<p>Товары без веса</p>
<table>";
if (!empty($list)){
   foreach($list as $item){
        echo "<tr>
            <td>
               ".$item['id']."
            </td>
            <td>
               ".$item['title']."
            </td>
            <td>
               ".$item['barcode']."
            </td>
        </tr>";
   }
}
echo "</table>";

 SELECT id,wp.title,barcode,wpl.prop_id,wpl.val_str,wpl.val_int FROM wlzd_product wp,  wlzd_product_prop_link  wpl WHERE
  wp.id=wpl.product_id AND 
  wpl.prop_id IN ( 342) AND -- список идентификаторов характеристик (Номера) через запятую
  (wpl.val_int IS NULL OR wpl.val_int=0) -- если строковая переменная, то вместо val_int  будет  val_str

 SELECT id,wp.title,barcode FROM wlzd_product wp WHERE wp.weight IN ('',0, ' ') OR wp.weight IS null