| From: | Jeff Janes <jeff(dot)janes(at)gmail(dot)com> |
|---|---|
| To: | Dmitry Lazurkin <dilaz03(at)gmail(dot)com> |
| Cc: | "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com>, "pgsql-general(at)postgresql(dot)org" <pgsql-general(at)postgresql(dot)org> |
| Subject: | Re: Perfomance of IN-clause with many elements and possible solutions |
| Date: | 2017-07-31 16:42:50 |
| Message-ID: | CAMkU=1we8pXTzUaxY7d7T7ww9s74sjU+mje=yHi=8gH7Zix6Pg@mail.gmail.com |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-general |
On Mon, Jul 24, 2017 at 3:12 PM, Dmitry Lazurkin <dilaz03(at)gmail(dot)com> wrote:
> On 25.07.2017 00:31, David G. Johnston wrote:
>
>
> Basically you want to write something like:
>
> SELECT *
> FROM ids
> JOIN ( :values_clause ) vc (vid) ON (vc.vid = ids.id)
>
> or
>
> WITH vc AS (SELECT vid FROM .... ORDER BY ... LIMIT )
> SELECT *
> FROM ids
> JOIN vc ON (vid = ids.id)
>
>
> This query uses JOIN plan node as IN (VALUES ...).
>
> And I have one question. I don't understand why IN-VALUES doesn't use
> Semi-Join? PostgreSQL has Hash Semi-Join... For which task the database
> has node of this type?
>
>
I think it is simply because no one has gotten around to implementing it
that way. When you can just write it as a values list instead, the
incentive to make the regular in-list work better is not all that strong.
Cheers,
Jeff
| From | Date | Subject | |
|---|---|---|---|
| Next Message | Jeff Janes | 2017-07-31 17:08:47 | Re: Perfomance of IN-clause with many elements and possible solutions |
| Previous Message | Thomas Güttler | 2017-07-31 10:45:24 | Re: Row based permissions: at DB or at Application level? |