SELECT 
    i.ITEM_CODE,
    CASE
        WHEN i.ITEM_NAME = ih.ITEM_NAME or ih.ITEM_NAME IS NULL THEN i.ITEM_NAME
        ELSE NULL
    END AS ITEM_NAME
FROM ITEM as i
LEFT JOIN 
    (
        SELECT
            ITEM_CODE,
            ITEM_NAME
        FROM  ITEM_HISTORY
    ) as ih
ON i.ITEM_CODE = ih.ITEM_CODE
ORDER BY i.ITEM_CODE DESC
;