How to : rownum and order by in select statement

Question

Say I have a select statement with additional 'order by' clause.
The result set I want prepended by the rownum column.
But, and here comes the flaw, I want the rownum for the already ordered result set
not the unordered.
An example:
select firstname, lastname from myTable order by lastname;
When I add the rownum to the select clause,
'select rownum, firstname, lastname from myTable order by lastname;'
I might get something like:
20 Mike Adams
13 Nina Bravo
1 Tom Charlie
But I want the following result:
1 Mike Adams
2 Nina Bravo
3 Tom Charlie
I could now
'Select rownum, lastname, firstname from (select firstname, lastname from myTable order by lastname);
But I guess there is a better way!?!
which is the best way to accomplish that?
Thanks for your advice!

Answer 1

>
'Select rownum, lastname, firstname from (select firstname, lastname from myTable order by lastname)
>
Well if you ask me there is very little difference between this query and the above query
select rownum, lastname, firstname from mytable;Because rownum is assigned before the order by. The difference is in your query you are assigning a rownum to an ordered resultset but still there is no guarantee oracle is going to read the data in an ordered fashion. In the second query rownum is assigned to an unordered resultset. Again it is the samething. So if you want to guarantee it then I will go for the following option
select row_number() over(order by lastname) rn, lastname, firstname from mytable
order by lastnameAlso check this link.
http://www.oracle.com/technology/oramag/oracle/07-jan/o17asktom.html
Regards
Raj
Edited by: R.Subramanian on Jan 13, 2009 6:20 AM