select
*
from
(
select
coalesce(a.item_code,b.item_code) as CODE,
coalesce(a.item_name,b.item_name) as NAME,
case 
    when a.item_code is not null and b.item_code is null then
    'ADDED'
    when  b.item_code is not null and a.item_code is null then
    'DELETE'
    when a.item_code = b.item_code and 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 
) a
where a.COMP_RSLT is not null
order by 
CODE desc
;