Обсуждение: Quartile (etc) ranking in a SQL statement?

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Quartile (etc) ranking in a SQL statement?

От
Jeff Boes
Дата:
Here's a puzzler:

Given a query that returns rows ranked by some criteria, how can I write
another query around it that will give me the (say) first quartile (top
25%)?  Another way of putting it is: if I have rows that look like this:


aaa | 1251
aba | 1197
cax | 1042
... | ...
axq |  23
(142 rows)

How can I write a query that will return these as
 1 | aaa | 1251 2 | aba | 1197 3 | cax | 1042
... | ... | ...
142 | axq |  23

-- 
Jeff Boes                                      vox 616.226.9550 ext 24
Database Engineer                                     fax 616.349.9076
Nexcerpt, Inc.                                 http://www.nexcerpt.com          ...Nexcerpt... Extend your Expertise


Re: Quartile (etc) ranking in a SQL statement?

От
Jean-Luc Lachance
Дата:
In a PLPGPSQL script, once you know count(*) try 

execute ''select * from table limit '' || int4( theCount / 4);

If you want numbering, create a sequence and add nextval() to the query.

JLL



Jeff Boes wrote:
> 
> Here's a puzzler:
> 
> Given a query that returns rows ranked by some criteria, how can I write
> another query around it that will give me the (say) first quartile (top
> 25%)?  Another way of putting it is: if I have rows that look like this:
> 
> aaa | 1251
> aba | 1197
> cax | 1042
> ... | ...
> axq |  23
> (142 rows)
> 
> How can I write a query that will return these as
> 
>   1 | aaa | 1251
>   2 | aba | 1197
>   3 | cax | 1042
> ... | ... | ...
> 142 | axq |  23
> 
> --
> Jeff Boes                                      vox 616.226.9550 ext 24
> Database Engineer                                     fax 616.349.9076
> Nexcerpt, Inc.                                 http://www.nexcerpt.com
>            ...Nexcerpt... Extend your Expertise
> 
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