Oracle rownum (sql top) proper use

[Costas]

ROWNUM is a pseudocolumn (not a real column) that is available in a query. ROWNUM will be assigned the numbers 1, 2, 3, 4, ... N , where N is the number of rows.

--when running this, you will realize that the order by doesnt take place
select * from owner.customers where rownum < 232 order by lastmodified desc

 
 

--proper is :
select *
  from 
(select * 
   from owner.customers order by lastmodified desc)
 where ROWNUM < 232;

source - http://www.oracle.com/technetwork/issue-archive/2006/06-sep/o56asktom-086197.html