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To: Clem Dickey <dickeycl@us.ibm.com>
cc: pgsql-sql@postgresql.org
Subject: Re: "<query expression body> ::= <joined table>" grammar rule not
	accepted by Postgres
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Comments: In-reply-to Clem Dickey <dickeycl@us.ibm.com>
	message dated "Wed, 15 Jun 2011 14:50:09 -0700"
Date: Thu, 16 Jun 2011 01:59:12 -0400
Message-ID: <19449.1308203952@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Clem Dickey <dickeycl@us.ibm.com> writes:
> This expression is (I think) a well-formed query, but is rejected by
> Postgresql 8.4 (t is a table name).

>   t t1 NATURAL JOIN t t2;

Hmm ... I think you are looking at SQL92 or SQL99.  The later versions
of the spec don't seem to permit <joined table> to be used that way.
In particular, in SQL:2003 and SQL:2007 I don't see any derivation path
from <query expression> to <joined table>.  So while we possibly could
support this, it's legacy syntax, and I doubt there's enough interest to
bother.

[ digs a bit more... ]  Ah, here we are: Annex E of SQL:2003 calls out
various incompatibilities from SQL:99, notably

	6) In ISO/IEC 9075-2:1999, a <query expression body>, <query
	term>, or <query primary> could consist of a <joined
	table>. None of those three elements can consist of a <joined
	table> in this edition of ISO/IEC 9075.

			regards, tom lane