Re: assignment vs SELECT INTO

От: Andrew Dunstan
Тема: Re: assignment vs SELECT INTO
Дата: ,
Msg-id: 5457E614.1030902@dunslane.net
(см: обсуждение, исходный текст)
Ответ на: Re: assignment vs SELECT INTO  (Tom Lane)
Список: pgsql-performance

Скрыть дерево обсуждения

assignment vs SELECT INTO  (Andrew Dunstan, )
 Re: assignment vs SELECT INTO  (Tom Lane, )
  Re: assignment vs SELECT INTO  (Andrew Dunstan, )
 Re: assignment vs SELECT INTO  (Matheus de Oliveira, )

On 11/03/2014 03:24 PM, Tom Lane wrote:
> Andrew Dunstan <> 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.
>
>


Well, I accidetally left out this case:

    andrew=# do $x$ declare r abc; begin for i in 1 .. 10000000 loop
    select row('a','b',i) into r; end loop; end; $x$;
    DO
    Time: 81919.721 ms


which is slower still.

cheers

andrew




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