with cte as (
select ITEM_CODE,ITEM_NAME from ITEM
union
select ITEM_CODE,ITEM_NAME from ITEM_HISTORY
)
select
    b.ITEM_CODE as CODE
    ,b.ITEM_NAME as NAME
    ,case when i.ITEM_CODE is null then "DELETED"
        when h.ITEM_CODE is null then "ADD"
        when i.USER_UPDATE_DATETIME != h.USER_UPDATE_DATETIME then "UPDATED"
        else null end as COMP_RSLT
from
    cte as b
    left join
    ITEM as i
    on b.ITEM_CODE = i.ITEM_CODE
    left join
    ITEM_HISTORY as h
    on b.ITEM_CODE = h.ITEM_CODE
where
    COMP_RSLT is not null
order by
    CODE desc