Oracle rownum function

How I can get rownum in orac开发者_C百科le over order by name? i.e In SQL I have a query

  SELECT 
    ROW_NUMBER() OVER(ORDER BY FIRSTNAME) SRL

  FROM   
    [SECURITY].[USERS]

  ORDER BY 
    FIRSTNAME

How will it be in Oracle?

SELECT ROW_NUMBER() OVER(ORDER BY FIRSTNAME)SRL FROM USERS

In Oracle, ROWNUM refers to the current record in the result set (which should be ordered).

SELECT ROWNUM AS SRL
FROM USERS
ORDER BY FIRSTNAME

EDIT: THIS IS WRONG. ROWNUM is assigned BEFORE ordering.