Re: assignment vs SELECT INTO

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От Tom Lane
Тема Re: assignment vs SELECT INTO
Дата
Msg-id 25915.1415046245@sss.pgh.pa.us
обсуждение исходный текст
Ответ на assignment vs SELECT INTO  (Andrew Dunstan <andrew@dunslane.net>)
Ответы Re: assignment vs SELECT INTO  (Andrew Dunstan <andrew@dunslane.net>)
Список pgsql-performance
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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