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?

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

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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.