Can Rewrite Following Query Without Using Row_number() Function

can I rewrite the following query without using the 'ROW_NUMBER() OVER ' part.The query is supposed to pull out the records whose CODE is not NULL and has most recent date for UPDATE_DATE . The reason I wanted to do this is, When I embed this query in between many other queries along with JOINs, My oracle server is unable to execute. So, I thought its better to supplant 'ROW_NUMBER() OVER ' logic with something else and try it. .

CURRENT QUERY:
SELECT a.* FROM
(SELECT b.*, ROW_NUMBER() OVER (PARTITION BY b.PIDM
ORDER BY b.UPDATE_DATE DESC) AS Rno
FROM
(
SELECT *
FROM SHYNCRO WHERE CODE IS NOT NULL
)b
)a
WHERE a.Rno = 1