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Date: Mon, 25 Apr 2011 17:22:23 +0300
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Subject: Re: big distinct clause vs. group by
From: =?KOI8-U?B?96bUwcymyiD0yc3eydvJzg==?= <tivv00@gmail.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Uwe Bartels <uwe.bartels@gmail.com>,
	"pgsql-performance@postgresql.org" <pgsql-performance@postgresql.org>
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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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<br><br><div class=3D"gmail_quote">2011/4/23 Robert Haas <span dir=3D"ltr">=
&lt;<a href=3D"mailto:robertmhaas@gmail.com">robertmhaas@gmail.com</a>&gt;<=
/span><br><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;bord=
er-left:1px #ccc solid;padding-left:1ex;">
<div class=3D"im">On Apr 18, 2011, at 1:13 PM, Uwe Bartels &lt;<a href=3D"m=
ailto:uwe.bartels@gmail.com">uwe.bartels@gmail.com</a>&gt; wrote:<br>
&gt; Hi Robert,<br>
&gt;<br>
&gt; thanks for your answer.<br>
&gt; the aggregate function I was talking about is the function I need to u=
se for the non-group by columns like min() in my example.<br>
&gt; There are of course several function to choose from, and I wanted to k=
now which causes as less as possible resources.<br>
<br>
</div>Oh, I see. min() is probably as good as anything. You could also crea=
te a custom aggregate that just always returns its first input. I&#39;ve oc=
casionally wished we had such a thing as a built-in.<br><br></blockquote>
<div><br></div><div>I&#39;ve once done &quot;single&quot; grouping function=
 - it checks that all it&#39;s input values are equal (non-null ones) and r=
eturns the value or raises an error if there are two different values.=A0</=
div>
<div><br></div><div>Best regards, Vitalii Tymchyshyn=A0</div></div><br><br =
clear=3D"all"><br>-- <br>Best regards,<br>=A0Vitalii Tymchyshyn<br>

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