Re: Perfomance of IN-clause with many elements and possible solutions

["David G. Johnston" <david.g.johnston@xxxxxxxxx>]

On Mon, Jul 24, 2017 at 3:12 PM, Dmitry Lazurkin <dilaz03@xxxxxxxxx> wrote:

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?

​Semi-Join is canonically written as:

SELECT *

FROM tbl

WHERE EXISTS (SELECT 1 FROM tbl2 WHERE tbl.id = tbl2.id)

The main difference between IN and EXISTS is NULL semantics.

David J.