To: Andres Freund <andres@anarazel.de>, pgsql-hackers@postgresql.org,
	Thom Brown <thom@linux.com>, Dimitri Fontaine <dimitri@2ndquadrant.fr>
Subject: Re: Command Triggers, patch v11 
In-reply-to: <9503.1332006327@sss.pgh.pa.us> 
References: <m24nufq466.fsf@2ndQuadrant.fr>
	<201203162237.38813.andres@anarazel.de>
	<21818.1331934775@sss.pgh.pa.us>
	<201203162317.43818.andres@anarazel.de>
	<7094.1331996567@sss.pgh.pa.us> <9503.1332006327@sss.pgh.pa.us>
Comments: In-reply-to Tom Lane <tgl@sss.pgh.pa.us>
	message dated "Sat, 17 Mar 2012 13:45:27 -0400"
Date: Sat, 17 Mar 2012 18:04:30 -0400
Message-ID: <24814.1332021870@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

I've found a couple more issues in the CTAS patch:

1. Previous versions delivered a "SELECT n" command tag for either
spelling of the command:

regression=# select * into t1 from int8_tbl;
SELECT 6
regression=# create table t2 as select * from int8_tbl;
SELECT 6

With the patch I get

regression=# select * into t1 from int8_tbl;
SELECT 0 0
regression=# create table t2 as select * from int8_tbl;
CREATE TABLE AS

The first of these is particularly unfortunate since it's outright lying
as to the number of rows processed.

I'm not sure what we should do instead.  We have gotten push-back before
anytime we changed the command tag for an existing command (and in fact
it seems that we intentionally added the rowcount display in 9.0, which
means there are people out there who care about that functionality).
On the other hand, the traditional output for CREATE TABLE AS doesn't
seem to satisfy the principle of least astonishment.  A third
consideration is that if we are pushing CREATE TABLE AS as the preferred
spelling, people will probably complain if it omits functionality that
SELECT INTO provides; so I'm not sure that "SELECT n" in one case and
"CREATE TABLE AS" in the other would be a good idea either.  Any
opinions what to do here?

2. Historically, CREATE RULE has allowed a rule action to be SELECT INTO
(though not CREATE TABLE AS).  Currently the patch is throwing an error
for that.  This seems like something that might not be worth fixing,
though.  It's fairly hard to conceive of a use-case for such a rule,
since it would work only once before starting to throw "table already
exists" errors.  How much do we care about preserving backward
compatibility here?

			regards, tom lane