Message-ID: <4E8AB2D7.2010901@archidevsys.co.nz>
Date: Tue, 04 Oct 2011 20:16:39 +1300
From: Gavin Flower <GavinFlower@archidevsys.co.nz>
Organization: ArchiDevSys
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To: Vitalii Tymchyshyn <tivv00@gmail.com>
CC: bricklen <bricklen@gmail.com>, Merlin Moncure <mmoncure@gmail.com>,
	"pgsql-performance@postgresql.org" <pgsql-performance@postgresql.org>
Subject: Re: array_except -- Find elements that are not common to both arrays
References: 
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	<CAGrpgQ-Zo6FOtc=NtY-4wXcnYqQRgcRLDR3BGQk2nAXpW46rzA@mail.gmail.com>
	<4E85B4AF.2090104@gmail.com>
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On 01/10/11 01:23, Vitalii Tymchyshyn wrote:
> Since you are using except and not except all, you are not looking at 
> arrays with duplicates.
> For this case next function what the fastest for me:
>
> create or replace function array_except2(anyarray,anyarray) returns
> anyarray as $$
> select ARRAY(
> (
> select r.elements
> from    (
>         (select 1,unnest($1))
>         union all
>         (select 2,unnest($2))
>         ) as r (arr, elements)
>     group by 1
>     having min(arr)=max(arr)
> ))
> $$ language sql strict immutable;
>
> Best regards, Vitalii Tymchyshyn
>
Very neat!

I could see that this function could trivially be modified to handle 3 
arrays.

QUESTION: Could this be modified to take an arbitrary number of arrays?