From: | luis(dot)roberto(at)siscobra(dot)com(dot)br |
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To: | Klaudie Willis <Klaudie(dot)Willis(at)protonmail(dot)com> |
Cc: | pgsql-general <pgsql-general(at)lists(dot)postgresql(dot)org> |
Subject: | Re: Performance of "distinct with limit" |
Date: | 2020-08-28 11:59:08 |
Message-ID: | 1880175167.48585037.1598615948304.JavaMail.zimbra@siscobra.com.br |
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Thread: | |
Lists: | pgsql-general |
Hi,
If "n" is indexed, it should run quickly. Can you share the execution plan for your query?
De: "Klaudie Willis" <Klaudie(dot)Willis(at)protonmail(dot)com>
Para: "pgsql-general" <pgsql-general(at)lists(dot)postgresql(dot)org>
Enviadas: Sexta-feira, 28 de agosto de 2020 8:29:58
Assunto: Performance of "distinct with limit"
Hi,
Ran into this under-optimized query execution.
select distinct n from bigtable; -- Lets say this takes 2 minutes
select distinct n from bigtable limit 2 -- This takes approximately the same time
However, the latter should have the potential to be so much quicker. I checked the same query on MSSQL (with 'top 2'), and it seems to do exactly the optimization I would expect.
Is there any way to achieve a similar speedup in Postgresql?
Klaudie
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