From: Tom Lane <tgl@sss.pgh.pa.us>
To: ceharris@vt.edu
cc: pgsql-docs@lists.postgresql.org
Subject: Re: WITH RECURSIVE (Documentation section 7.8.1) Note
In-reply-to: <157002368762.1131.16941475162203318675@wrigleys.postgresql.org>
References: <157002368762.1131.16941475162203318675@wrigleys.postgresql.org>
Comments: In-reply-to PG Doc comments form <noreply@postgresql.org>
	message dated "Wed, 02 Oct 2019 13:41:27 -0000"
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Date: Wed, 02 Oct 2019 12:41:44 -0400
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PG Doc comments form <noreply@postgresql.org> writes:
> In section 7.8.1, the author comments "Note: Strictly speaking, this process
> is iteration not recursion, but RECURSIVE is the terminology chosen by the
> SQL standards committee."

I think I'm to blame for that wording.

> Example: R_2 = F(F(R_0))
> Example: R_5 = F(F(F(F(F(R_0))))
> This is textbook recursion, not just some folly of the ANSI standards
> committee as suggested by the note in the text.

No, it isn't.  F() is being applied repeatedly (iteratively).  If F()
called itself internally, that would be recursion.

Another way to look at this is that control of whether the repetition
is finished is external to the function/query.  If the stop condition
were part of the query logic, it'd be more sensible to think of it as
recursion, IMO.

			regards, tom lane