From: Vitalii Tymchyshyn <tivv00@gmail.com>
To: bricklen <bricklen@gmail.com>
Cc: Merlin Moncure <mmoncure@gmail.com>
Cc: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: array_except -- Find elements that are not common to both arrays
Date: Fri, 30 Sep 2011 15:23:11 +0300
Message-ID: <4E85B4AF.2090104@gmail.com> (raw)
In-Reply-To: <CAGrpgQ-Zo6FOtc=NtY-4wXcnYqQRgcRLDR3BGQk2nAXpW46rzA@mail.gmail.com>
References: <CAGrpgQ8YkMVpN1scWYbqBW+fdNhSpXFd9T7YqxmGCJKT3XHZnA@mail.gmail.com>
<CAHyXU0wVZ+0A7FCvYNcK_r9UTqutgpjE8MQHXAmb2uv7=0-QZQ@mail.gmail.com>
<CAGrpgQ-Zo6FOtc=NtY-4wXcnYqQRgcRLDR3BGQk2nAXpW46rzA@mail.gmail.com>
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
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To: pgsql-performance@postgresql.org
Cc: tivv00@gmail.com, bricklen@gmail.com, mmoncure@gmail.com
Subject: Re: array_except -- Find elements that are not common to both arrays
In-Reply-To: <4E85B4AF.2090104@gmail.com>
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