Re: median and percentile function implementation

On 08/26/2013 02:39 PM, Pavel Stehule wrote:
> Hello
>
> Three years ago we worked on implementation of median function.
>
> http://www.postgresql.org/message-id/AANLkTimRksUOgGsK7-gTXnvJJGL-1QvuqxidusZQwep6@mail.gmail.com
>
>
> Can we implement this function now?
>
> There are a few opened questions:
>
> * immutable parameters of aggregate functions
>
> * effective implementation when data are in memory
>
> * effective implementation when data are out of memory
>
> * effective implementation for usage as window function - running median.
>
> Better than before, we can choose between hashing and sorting based
> aggregation. But tuplesort implementation is not right for using as
> window function. Second issue can be a not possible reusing of
> tuplesort for more final functions - median, percentile in one query.
>
> Ideas how to solve this task? Can we move forward in some points?

Take a look at the standard-compliant WITHIN GROUP that is currently in
development for 9.4.
http://www.postgresql.org/message-id/2b8b55b8ba82f83ef4e6070b95fb0cd0@news-out.riddles.org.uk

--
Vik