To: Marco Nenciarini <marco.nenciarini@2ndQuadrant.it>
cc: pgsql-hackers@postgresql.org, Noah Misch <noah@leadboat.com>
Subject: Re: [PATCH] Support for foreign keys with arrays 
In-reply-to: <1332178899.2278.4.camel@greygoo.devise-it.lan> 
References: <4EC8CA0F.8040405@2ndQuadrant.it>
	<20111120130526.GD12013@tornado.leadboat.com>
	<4EE31CB9.90005@2ndQuadrant.it>
	<20111212004506.GB10399@tornado.leadboat.com>
	<1326568728.2613.16.camel@greygoo.devise-it.lan>
	<20120121204223.GA2388@tornado.leadboat.com>
	<4F280EFE.1080604@2ndQuadrant.it>
	<1328551482.3354.64.camel@greygoo.devise-it.lan>
	<20120225020135.GA27204@tornado.leadboat.com>
	<1331748188.6744.15.camel@greygoo.devise-it.lan>
	<20120317033312.GB19556@tornado.leadboat.com>
	<1332178899.2278.4.camel@greygoo.devise-it.lan>
Comments: In-reply-to Marco Nenciarini <marco.nenciarini@2ndQuadrant.it>
	message dated "Mon, 19 Mar 2012 18:41:39 +0100"
Date: Thu, 22 Mar 2012 15:02:45 -0400
Message-ID: <12609.1332442965@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

Marco Nenciarini <marco.nenciarini@2ndQuadrant.it> writes:
> Attached is v5, which should address all the remaining issues.

I started to look at this patch a bit.  I'm quite confused by the fact
that some, but not all, of the possible FK action types now come in an
EACH variant.  This makes no sense at all to me.  ISTM that EACH is a
property of the FK constraint as a whole, that is that it says the
constraint is from array elements on the referencing side to column
values on the referenced side, rather than the normal case of column
values to column values.  Why would the possible actions be affected,
and why only these?  The patch documentation is extremely unclear about
this.  It's even less clear about what the semantics are in multi-key
cases.  Right offhand I would say that multi-key cases are nonsensical
and should be forbidden outright, because there is no way to figure out
which collections of elements of different arrays should be considered
to be a referencing item.

Could we see a specification of what the referencing semantics are
intended to be, please?

			regards, tom lane