From: Віталій Тимчишин <tivv00@gmail.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Uwe Bartels <uwe.bartels@gmail.com>
Cc: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: big distinct clause vs. group by
Date: Mon, 25 Apr 2011 17:22:23 +0300
Message-ID: <BANLkTimV3yEF_Dq6rA+m0tfYkFAwwwYNPA@mail.gmail.com> (raw)
In-Reply-To: <4B594466-0554-4AF8-A8BC-8FDA9C393DF9@gmail.com>
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<4B594466-0554-4AF8-A8BC-8FDA9C393DF9@gmail.com>
2011/4/23 Robert Haas <robertmhaas@gmail.com>
> On Apr 18, 2011, at 1:13 PM, Uwe Bartels <uwe.bartels@gmail.com> wrote:
> > Hi Robert,
> >
> > thanks for your answer.
> > the aggregate function I was talking about is the function I need to use
> for the non-group by columns like min() in my example.
> > There are of course several function to choose from, and I wanted to know
> which causes as less as possible resources.
>
> Oh, I see. min() is probably as good as anything. You could also create a
> custom aggregate that just always returns its first input. I've occasionally
> wished we had such a thing as a built-in.
>
>
I've once done "single" grouping function - it checks that all it's input
values are equal (non-null ones) and returns the value or raises an error if
there are two different values.
Best regards, Vitalii Tymchyshyn
--
Best regards,
Vitalii Tymchyshyn
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To: pgsql-performance@postgresql.org
Cc: tivv00@gmail.com, robertmhaas@gmail.com, uwe.bartels@gmail.com
Subject: Re: big distinct clause vs. group by
In-Reply-To: <BANLkTimV3yEF_Dq6rA+m0tfYkFAwwwYNPA@mail.gmail.com>
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