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