SELECT
    i.ITEM_CODE as CODE,
    case
     when h.ITEM_NAME ='null' then i.ITEM_NAME
     when i.ITEM_NAME <> h.ITEM_NAME then i.ITEM_NAME 
     else 'NULL'
    END as NAME
FROM
    ITEM as i
    LEFT JOIN ITEM_HISTORY as h
    on i.ITEM_CODE = h.ITEM_CODE
ORDER BY
    CODE desc