Re: MEDIAN as custom aggregate?

Can't you do something like

select age from ages order by age limit 1 offset (select count(*) from ages)/2;

except you can't nest the select so you'll have to use a variable to hold it...

Make sure it does the right thing when there is an odd number of rows.


I don't understand why you want the median and not some parameters of your assumed distribution (mean and variance, for
example)but each to his own...
 


Allan.

Josh Berkus wrote:

> Folks,
>
> Hey, anybody have a custom aggregate for median calucation?  I'm doing
> this through a PL/pgSQL function, and a custom aggregate would probably
> be faster.
>
> For those whose stats terminology is rusty, the "median" is the "middle"
> value in a distribution.  For example, if we had the following data:
>
> Table ages
> person          age
> Jim             21
> Rusty           24
> Carol           37
> Bob             62
> Leah            78
>
> Our Median would be Carol's age, 37.  This is a different figure from
> the Mean, or Average, which is 44.4.  Using the combination of the Mean
> and the Median you can do all kinds of interesting statistical analysis.
>
> -Josh Berkus
>
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