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Re: [COMMITTERS] pgsql: Add notion of a "transform function" that can simplify function

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Noah Misch <noah(at)leadboat(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: [COMMITTERS] pgsql: Add notion of a "transform function" that can simplify function
Date: 2012-03-23 15:36:49
Message-ID: 13690.1332517009@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-committerspgsql-hackers
Noah Misch <noah(at)leadboat(dot)com> writes:
> On Fri, Mar 23, 2012 at 10:55:52AM -0400, Tom Lane wrote:
>> Why exactly was this thought to be a good idea:
>> 
>>> * A NULL original expression disables use of transform functions while
>>> * retaining all other behaviors.

> I did it that way because it looked wrong to pass the same CoerceViaIO node to
> transforms of both the input and output functions.  Thinking about it again
> now, doing so imposes no fundamental problems.  Feel welcome to change it.

Oh, I see your point --- it's not obvious whether the current transform
is meant for the input or the output function.  Which is a very good
point.  In principle the transform function could figure out which end
of that it must be, but it would be ugly.

However, see my response to Robert: why are we passing the original node
to the transform function at all?  It would be more useful and easier to
work with to pass the function's fully-processed argument list, I believe.

			regards, tom lane

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