select
    coalesce(i.item_code,ih.item_code) as CODE
    , coalesce(i.item_name,ih.item_name) as NAME
    , case
        when ih.user_update_datetime is null then 'ADDED'
        when i.user_update_datetime is null then 'DELETED'
        when i.user_update_datetime<>ih.user_update_datetime then 'UPDATED'
      end as COMP_RSLT
from item i
full outer join item_history ih on i.item_code=ih.item_code
where i.user_update_datetime is not ih.user_update_datetime
order by code desc;