begin atomic
declare max_id int default  1 ;
for vv as
(SELECT ....)
do
  select max(id) into max_id from articuls_dm
   where articul_code = vv.articul_code and bar_code = vv.barcode;
  ....
end for;
end@

select max(id) into max_id
select max(id) as max_id into max_id
select max(id) into :max_id

SQL0104N  Обнаружен неправильный элемент "max_id" после текста "select max(id) into".  Список возможных правильных элементов: "<space> 

set max_id = (select max(id) from articuls_dm where articul_code = vv.articul_code and bar_code = vv.barcode);