From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alvaro Herrera <alvherre@2ndquadrant.com>
cc: keith.fiske@crunchydata.com, pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #15865: ALTER TABLE statements causing "relation already
 exists" errors when some indexes exist
In-reply-to: <28827.1561082086@sss.pgh.pa.us>
References: <20190620204505.GA22934@alvherre.pgsql>
 <25354.1561064909@sss.pgh.pa.us> <905.1561076455@sss.pgh.pa.us>
 <28827.1561082086@sss.pgh.pa.us>
Comments: In-reply-to Tom Lane <tgl@sss.pgh.pa.us>
	message dated "Thu, 20 Jun 2019 21:54:46 -0400"
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Date: Fri, 21 Jun 2019 12:47:55 -0400
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I wrote:
> BTW, has anyone got an explanation for the order in which psql is
> listing the indexes of "anothertab" in this test case?

Ah, here's the explanation: describe.c is sorting the indexes
with this:

	"ORDER BY i.indisprimary DESC, i.indisunique DESC, c2.relname;"

I can see the point of putting the pkey first, I guess, but the preference
for uniques second seems pretty bizarre, especially since
(a) it doesn't distinguish unique constraints from plain unique indexes and
(b) there's no similar preference for exclusion constraints, even though
those might be morally equivalent to a unique constraint.

What do people think of dropping the indisunique sort column here?
Obviously not back-patch material, but it might be more sensible
behavior going forward.

			regards, tom lane