Re: wip: functions median and percentile

2010/10/12 Hitoshi Harada <umi.tanuki@gmail.com>:
> 2010/10/12 Pavel Stehule <pavel.stehule@gmail.com>:
>> Hello
>>
>> 2010/10/11 Greg Stark <gsstark@mit.edu>:
>>> On Sun, Oct 10, 2010 at 2:16 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>>>> It was pointed out upthread that while median isn't presently
>>>> in the standard, Oracle defines it in terms of percentile_cont(0.5)
>>>> which *is* in the standard.
>>>
>>> Uhmm, then why don't we implement that? We could provide median() as a
>>> short-cut but percentile_cont() doesn't sound much harder to implement
>>> than median() and more general.
>>
>> The problem is in interface. The original patch did it, but I removed
>> it. We cannot to unsure immutability of some parameters now. Can we
>> enhance a AGGREGATE to allow some mark like IMMUTABLE parameter and
>> probably we should to support ANSI syntax:
>>
>> PERCENTILE_CONT ( expression1 )
>> WITHIN GROUP ( ORDER BY expression2 [ ASC | DESC ] )
>>
>> This syntax allows to divide a muttable and immutable parameters.
>
> If this is only a syntax sugar for mutable/immutable parameter, then I
> guess it's time to take it serious to implement in our syntax,
> although I'm not sure if it affects more execution model than
> interface.

I though about it, the question is an interface for PL languages.
There are not problem for C.

Regards

Pavel Stehule


>
> Regards,
>
>
>
> --
> Hitoshi Harada
>