RE: How to do a Top-N analysis, while avoiding subqueries

Hi Muhammed  

It's just a case study. Is it possible to do without the sub query?  

Actually, the original question is not from me, but from a friend of mine. I was just thinking about a good solution all morning long and couldn't figure out a good answer to the question.  

I find it quite reasonable to try a simple thing like a Top-N analysis without the use of a (possibly costly) sub query.  

But maybe I'm just spoiled by the proprietary MySQL feature of LIMIT BY...  

Regards,

Tristan  

Tristan van Essen

Accenture Technology Solutions AG

Baslerstrasse 60

CH-8048 Zürich

Office: +41 44 405 3245

Mobile: +41 79 654 0592

Email: tristan.van.essen_at_accenture.com

From: Muhammed Soyer [mailto:msoyer_at_gmail.com] Sent: Mittwoch, 7. Juni 2006 12:02
To: van Essen, Tristan
Cc: oracle-l_at_freelists.org
Subject: Re: How to do a Top-N analysis, while avoiding subqueries  

Why dont you want to use sub queries ? Any solid reason or just for curiosity ..

2006/6/7, tristan.van.essen_at_accenture.com <tristan.van.essen_at_accenture.com>:

Hi folks, this is my first question in this mailing list.  

How do you do a top-n analysis while avoiding subqueries, but still use group functions on other columns?  

I have following Query:  

SELECT COUNT(city) quantity, city

FROM customer

GROUP BY city

ORDER BY quantity DESC;

This works fine so far with the exception that I only want the first record returned, instead of all. I tried to solve the problem with the ROWNUM function, but it won't work well. The problem here is that I must include ROWNUM in the GROUP BY clause, else the query fails. But then the result isn't right anymore. I wish there was any sort of LIMIT BY clause, like there is in MySQL.  

How can I solve this, while not using any subqueries?  

Regards,

Tristan    

Tristan van Essen

Accenture Technology Solutions AG

Baslerstrasse 60

CH-8048 Zürich

Office: +41 44 405 3245

Mobile : +41 79 654 0592

Email: tristan.van.essen_at_accenture.com  

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