Date: Thu, 11 Oct 2018 13:39:52 -0300
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Robert Haas <robertmhaas@gmail.com>,
	Jeevan Chalke <jeevan.chalke@enterprisedb.com>,
	pgsql-hackers@lists.postgresql.org,
	David Rowley <david.rowley@2ndquadrant.com>
Subject: Re: Soon-to-be-broken regression test case
Message-ID: <20181011163952.emtpcrzkpselhupj@alvherre.pgsql>
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On 2018-Oct-11, Tom Lane wrote:

> I have been fooling around with a patch to allow pull-up of sub-selects
> that lack any FROM, along the lines discussed in
> https://www.postgresql.org/message-id/15944.1521127664@sss.pgh.pa.us
> I find that it is smart enough to reduce that EXISTS to a plain
> expression, yielding
> 
>                      QUERY PLAN                     
> ----------------------------------------------------
>  Subquery Scan on tenk1_vw_sec
>    ->  Index Only Scan using tenk1_unique1 on tenk1
>          Index Cond: (unique1 = 0)
> (3 rows)

Hmm, I have the feeling that this would nullify some tests in
partition_prune also, which IIRC pretend to invoke runtime pruning with
things like "WHERE partcol = (select 1)".

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services