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From: David Rowley <[email protected]>
To: Peter Eisentraut <[email protected]>
Cc: pgsql-hackers <[email protected]>
Subject: Re: Optimize SELECT * in EXISTS
Date: Mon, 23 Feb 2026 21:41:22 +1300
Message-ID: <CAApHDvprYAAA1szsC3+OYWss4ALJp0wG7Qbw8Zu+s7pq1gm3yA@mail.gmail.com> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>

On Mon, 23 Feb 2026 at 21:21, Peter Eisentraut <[email protected]> wrote:
> I read in the SQL standard that SELECT * in EXISTS is not supposed to be
> expanded to all columns, but only to an arbitrary literal.  This
> corresponds to the recommendation in the PostgreSQL documentation to
> write EXISTS (SELECT 1 ...) instead.  But not even our own tests and
> example code use that latter convention consistently, so I think many
> users don't know it or observe it either.  So implementing that little
> optimization for SELECT * seems reasonable.

> Thoughts?

Don't we already do this in simplify_EXISTS_query()?

David

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