DELETE
FROM
    ITEM
WHERE
    ITEM_CODE NOT IN (SELECT ITEM_CODE FROM STOCK)
    OR ITEM_CODE IN (SELECT 
            MAX(LAST_DELIVERY_DATE) 
        FROM 
            STOCK 
        WHERE 
            LAST_DELIVERY_DATE >= 6 
            AND ACTUAL_AMT = 0
        GROUP BY 
            ITEM_CODE
            )