delete from
    ITEM
where
    not exists(
        select
            ITEM_CODE
        from
            STOCK
        where
            ITEM.ITEM_CODE = STOCK.ITEM_CODE
    )
    or 
    exists(
        select
            ITEM_CODE
        from
            STOCK
        where
            ITEM.ITEM_CODE = STOCK.ITEM_CODE
        and LAST_DELIVERY_DATE <= date(LAST_DELIVERY_DATE, '-6 months')
        and ACTUAL_AMT = 0
    )