Re: insert on conflict on updatable views

From: Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>
To: Peter Geoghegan <pg(at)bowt(dot)ie>
Cc: Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: insert on conflict on updatable views
Date: 2018-08-02 04:06:41
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On 2018/08/02 11:24, Peter Geoghegan wrote:
> On Wed, Aug 1, 2018 at 7:15 PM, Amit Langote
> <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp> wrote:
>> create table foo (a int unique, b text);
>> create view foo_view as select b, a+1 as c, a from foo;
>> explain insert into foo_view (a, b) select 1, 2 on conflict (a) do update
>> set b = excluded.b where excluded.c > 0;
>> IOW, the EXCLUDED pseudo-relation should only allow referencing the
>> columns present in the underlying physical relation. Thoughts?
> EXCLUDED represents the values that the user attempted to insert, so
> it's arguably useful that EXCLUDED.c is accessible here, even though
> the target rel doesn't have a "c" column.

Maybe it's OK while we're still in the parser, where as long as parser
transformation doesn't find that EXCLUDED.c is problematic, we won't emit
an error. That is, as long as transformExpr() applied to OnConflictClause
can resolve "c", there is nothing to complain about.


> Do you have some particular practical problem in mind here, or are you
> just concerned about the semantics being exactly consistent?

Once we get to the rewriter, where the INSERT on the view is transformed
into into one on the underlying physical relation, then it's clear which
columns we can go ahead with (and which ones we cannot). In fact,
rewriteTargetView() even forbids inserting into columns that are not
present in the underlying relation. So, from this point on, ON CONFLICT
handling code cannot rely on being able to compute the columns not present
in the underlying relation.


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