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Re: big distinct clause vs. group by

From: Uwe Bartels <uwe(dot)bartels(at)gmail(dot)com>
To: Віталій Тимчишин <tivv00(at)gmail(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org>
Subject: Re: big distinct clause vs. group by
Date: 2011-04-25 19:01:09
Message-ID: BANLkTikNf0fnrrZfUY6SdUQuGKSpdR5AcQ@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
Hi Vitalii,

this sounds promising, can you send me that?

Best Regards,
Uwe


2011/4/25 Віталій Тимчишин <tivv00(at)gmail(dot)com>

>
>
> 2011/4/23 Robert Haas <robertmhaas(at)gmail(dot)com>
>
>> On Apr 18, 2011, at 1:13 PM, Uwe Bartels <uwe(dot)bartels(at)gmail(dot)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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