delete from ITEM 
where
not exists (
select 1 from stock s2
where 
ITEM.item_code = s2.item_code
and 

 ( (s2.LAST_DELIVERY_DATE > datetime('2023-06-01','-6 month')) or
 (s2.LAST_DELIVERY_DATE <= datetime('2023-06-01','-6 month') and ACTUAL_AMT=0
) )
)

;