Re: wip: functions median and percentile

Robert Haas <robertmhaas@gmail.com>

From: Robert Haas <robertmhaas@gmail.com>

To: Tom Lane <tgl@sss.pgh.pa.us>

Cc: Dean Rasheed <dean.a.rasheed@gmail.com>, Hitoshi Harada <umi.tanuki@gmail.com>, Greg Stark <gsstark@mit.edu>, Pavel Stehule <pavel.stehule@gmail.com>, David Fetter <david@fetter.org>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>

Date: 2010-10-11T10:33:12Z

Lists: pgsql-hackers

On Sun, Oct 10, 2010 at 5:16 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.  What I read in SQL:2008 is that
> percentile_cont is defined for all numeric types (returning
> approximate numeric with implementation-defined precision),
> and for interval (returning interval), and not for any other
> input type.  So it appears to me that what we ought to support
> is
>        median(float8) returns float8
>        median(interval) returns interval
> and nothing else --- we can rely on implicit casting to convert
> any other numeric input type to float8.

Isn't there a possibility of a precision loss if numeric gets cast to
float8?  Should we include an explicit variant from numeric?

-- 
Robert Haas
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