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From: Tom Lane <[email protected]>
To: [email protected]
Cc: [email protected]
Subject: Re: <from_item> doc has self referential definition
Date: Wed, 03 Jan 2018 22:33:39 -0500
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>

=?utf-8?q?PG_Doc_comments_form?= <[email protected]> writes:
> https://www.postgresql.org/docs/9.6/static/sql-select.html

> The last line for <from_item> breaks the group.  There should be something
> like:

> <from_item>
>    <join_from>
>    <simple_from>

> (with better naming).

Hm, I can't get excited about it.  You're correct that the grammar
as stated is ambiguous, and if we introduced another level of
nonterminal we could make it reflect the left-to-right precedence
of join operators ... but I think 99% of our users would just find
it more confusing that way.  The existing statement in the text that
"In the absence of parentheses, JOINs nest left-to-right" is probably
clearer to most people than a formal grammar for it would be.

(Heck, even our actual bison grammar file relies on precedence to
define this behavior, rather than an extra nonterminal ... and you
can't get much nerdier than a bison grammar.)

			regards, tom lane

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