Re: [GENERAL] Perfomance of IN-clause with many elements and possiblesolutions - Mailing list pgsql-general

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?