Top N Analysis

[yogesh sood]

Hi,
a simple query..
How to find top N salary from emp table, without using sub queries and inline view.....

[Mark Spritzler]

Order by the field that you want the top in, then use the "rownum" keyword in the where clause.
As is
Select name, salary
from emp
where rownum < 10
order by salary desc

Mark

[yogesh sood]

hi thanks for reply...
But i think rownum is assigned every time you reorder the records in cursors.therefore if im using order by after row num then new row num will be assigned after applying oreder by...
correct me if im wrong

[Mark Spritzler]

negative, Rownum is not determined till after the ordering is done.
Mark

[Loren Rosen]

Using rownums here can be a bit problematic if you're concerned about ties (since many employees can have the same salary). Oracle does have special support for top n queries taking ties into account. Unless they've reorganized the docs since I last looked at it a few years ago this is described in the "data warehousing guide" in the Oracle DB doc set. Look for words like "rank" and "ranking"

[John Colton]

negative, Rownum is not determined till after the ordering is done.

I don't think this is correct. You have to use a subquery to get the results you want, because sorting happens after the rownum assignment as so:

select name, salary
from (select name, salary
from emp
order by salary desc)
where rownum<10

I remember having a question like this for the 007 cert exam.

John