Message-ID: <4E85B4AF.2090104@gmail.com>
Date: Fri, 30 Sep 2011 15:23:11 +0300
From: Vitalii Tymchyshyn <tivv00@gmail.com>
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To: bricklen <bricklen@gmail.com>
CC: 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
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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