--kontrol
    SELECT 
        A.order_start 
        , B.order_start
FROM
    ZT_Indirimli AS A -- kendi tablo adınız.
    INNER JOIN ZT_Indirimli AS B
        ON A.order_url = B.order_url
WHERE
    B.order_start<>'0'

--güncelleme
UPDATE
    A
SET
    A.order_start = B.order_start
FROM
    ZT_Indirimli AS A
    INNER JOIN ZT_Indirimli AS B
        ON A.order_url = B.order_url
WHERE
    B.order_start<>'0'