Date: Wed, 8 Feb 2017 09:15:02 -0800
From: David Fetter <david@fetter.org>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Robert Haas <robertmhaas@gmail.com>,
	Pantelis Theodosiou <ypercube@gmail.com>,
	Joel Jacobson <joel@trustly.com>,
	Pg Hackers <pgsql-hackers@postgresql.org>
Subject: Re: Idea on how to simplify comparing two sets
Message-ID: <20170208171502.GA10277@fetter.org>
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On Wed, Feb 08, 2017 at 11:22:56AM -0500, Tom Lane wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
> > On Wed, Feb 8, 2017 at 4:24 AM, Pantelis Theodosiou <ypercube@gmail.com> wrote:
> >> I'm not advocating it but I don't see how introducing new SQL keywords
> >> breaks backwards compatibility.
> 
> > It does at least a little bit.
> 
> Yes.  I think a new set-operation keyword would inevitably have to
> be fully reserved --- UNION, INTERSECT, and EXCEPT all are --- which
> means that you'd break every application that has used that word as
> a table, column, or function name.

I've long wanted a SYMMETRIC DIFFERENCE join type, that being the only
elementary set operation not included in join types, but nobody at the
SQL standards committee seems to have cared enough to help.

> Generally speaking, we try very darn hard not to introduce new
> reserved words that are not called out as reserved in the SQL
> standard.  (And even for those, we've sometimes made the grammar
> jump through hoops so as not to reserve a word that we didn't
> reserve previously.)

We just never know what new keywords the standards committee will
dream up, or what silliness they'll introduce in the grammar :/

Best,
David.
-- 
David Fetter <david(at)fetter(dot)org> http://fetter.org/
Phone: +1 415 235 3778  AIM: dfetter666  Yahoo!: dfetter
Skype: davidfetter      XMPP: david(dot)fetter(at)gmail(dot)com

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