From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andrew Dunstan <andrew@dunslane.net>
cc: pgsql-perform <pgsql-performance@postgresql.org>
Subject: Re: assignment vs SELECT INTO
In-reply-to: <5457DECE.3070302@dunslane.net>
References: <5457DECE.3070302@dunslane.net>
Comments: In-reply-to Andrew Dunstan <andrew@dunslane.net>
 message dated "Mon, 03 Nov 2014 15:00:14 -0500"
Date: Mon, 03 Nov 2014 15:24:05 -0500
Message-ID: <25915.1415046245@sss.pgh.pa.us>
Precedence: bulk
Sender: pgsql-performance-owner@postgresql.org

Andrew Dunstan <andrew@dunslane.net> writes:
>     andrew=# do $x$ declare r abc; begin for i in 1 .. 10000000 loop
>     select 'a','b',i into r.x,r.y,r.z; end loop; end; $x$;
>     DO
>     Time: 63731.434 ms
>     andrew=# do $x$ declare r abc; begin for i in 1 .. 10000000 loop r
>     := ('a','b',i); end loop; end; $x$;
>     DO
>     Time: 18744.151 ms

> Is it simply because the SELECT is in effect three assignments, so it 
> takes nearly 3 times as long?

I think it's more likely that the second example is treated as a "simple
expression" so it has less overhead than a SELECT.

			regards, tom lane


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