with ad as (
select  ITEM_CODE AS CODE
       ,ITEM_NAME AS NAME
       ,"ADD" AS COMP_RSLT
from item i
where not exists (
select * from item_history ih
where i.item_code = ih.item_code))

,upd as (
select  ITEM_CODE AS CODE
       ,ITEM_NAME AS NAME
       , "UPDATE" AS COMP_RSLT
from item i
where exists (
select * from item_history ih
where i.item_code = ih.item_code
and   i.USER_UPDATE_DATETIME <> ih.USER_UPDATE_DATETIME))

,del as (
select  ITEM_CODE AS CODE
       ,ITEM_NAME AS NAME
       ,"DELETE" AS COMP_RSLT
from item ih
where not exists (
select * from item_history i
where i.item_code = ih.item_code))

select *
from ad
union
select *
from upd
union
select *
from del