Hi,
If "n" is indexed, it should run quickly. Can you share the execution plan for your query?
De: "Klaudie Willis" <Klaudie.Willis@xxxxxxxxxxxxxx>
Para: "pgsql-general" <pgsql-general@xxxxxxxxxxxxxxxxxxxx>
Enviadas: Sexta-feira, 28 de agosto de 2020 8:29:58
Assunto: Performance of "distinct with limit"
Para: "pgsql-general" <pgsql-general@xxxxxxxxxxxxxxxxxxxx>
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
