Date: Tue, 3 Jan 2017 19:21:49 -0300
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Justin Pryzby <pryzby@telsasoft.com>,
	Robert Haas <robertmhaas@gmail.com>,
	"pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Subject: Re: ALTER TABLE .. ALTER COLUMN .. ERROR: attribute .. has
 wrong type
Message-ID: <20170103222149.azbla6jtpnh2ublg@alvherre.pgsql>
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Tom Lane wrote:

> A little bit of "git bisect"-ing later, the blame is pinned on
> 
> commit 9550e8348b7965715789089555bb5a3fda8c269c
> Author: Alvaro Herrera <alvherre@alvh.no-ip.org>
> Date:   Fri Apr 3 17:33:05 2015 -0300
> 
>     Transform ALTER TABLE/SET TYPE/USING expr during parse analysis
>     
>     This lets later stages have access to the transformed expression; in
>     particular it allows DDL-deparsing code during event triggers to pass
>     the transformed expression to ruleutils.c, so that the complete command
>     can be deparsed.
>     
>     This shuffles the timing of the transform calls a bit: previously,
>     nothing was transformed during parse analysis, and only the
>     RELKIND_RELATION case was being handled during execution.  After this
>     patch, all expressions are transformed during parse analysis (including
>     those for relkinds other than RELATION), and the error for other
>     relation kinds is thrown only during execution.  So we do more work than
>     before to reject some bogus cases.  That seems acceptable.
> 
> Of course, the reason why this work was postponed until execution was
> exactly because we wanted to do it over again for each child table.
>
> We could probably fix the specific issue being seen here by passing the
> expression tree through a suitable attno remapping,

Hmm, ouch.  I can look into fixing this starting tomorrow afternoon.

> but I am now filled with dread about how much of the event trigger
> code may be naively supposing that child tables have the same attnums
> as their parents.

I guess it's on me to figure that out.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services


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