Re: Potentially undocumented behaviour change in Postgres 11 concerning OLD record in an after insert trigger

On 1/4/19 4:20 AM, Kristjan Tammekivi wrote:
> Hi,
> I've read the documentation, that's why I said this might be 
> undocumented. Try the SQL in Postgres 11 and see that it works for yourself.
> I have an analogous trigger in production from yesterday and I've tested 
> it in local environment as well.

I can confirm:

select version();
                                       version 

------------------------------------------------------------------------------------
  PostgreSQL 11.1 on x86_64-pc-linux-gnu, compiled by gcc (SUSE Linux) 
4.8.5, 64-bit


INSERT INTO _tmp_test1 (val) VALUES (5);
INSERT 0 1

select * from _tmp_test1_changes ;
  id |         changes
----+-------------------------
   1 | "id"=>NULL, "val"=>NULL
(1 row)

I would file a bug report:

https://www.postgresql.org/account/submitbug/

> 
> On Fri, Jan 4, 2019 at 12:56 PM Charles Clavadetscher 
> <clavadetscher@swisspug.org <mailto:clavadetscher@swisspug.org>> wrote:
> 
>     Hello____
> 
>     __ __
> 
>     *From:*Kristjan Tammekivi <kristjantammekivi@gmail.com
>     <mailto:kristjantammekivi@gmail.com>>
>     *Sent:* Freitag, 4. Januar 2019 11:46
>     *To:* pgsql-general@postgresql.org <mailto:pgsql-general@postgresql.org>
>     *Subject:* Potentially undocumented behaviour change in Postgres 11
>     concerning OLD record in an after insert trigger____
> 
>     __ __
> 
>     Hi,____
> 
>     __ __
> 
>     I've noticed a change in the behaviour in triggers / hstores in
>     Postgres 11.1 when compared to Postgres 10.5.____
> 
>     The following won't work on Postgres 10.5 but in Postgres 11.1 it
>     works just fine:____
> 
>     __ __
> 
>     CREATE EXTENSION hstore;
> 
>     CREATE TABLE _tmp_test1 (id serial PRIMARY KEY, val INTEGER);
>     CREATE TABLE _tmp_test1_changes (id INTEGER, changes HSTORE);
> 
>     CREATE FUNCTION test1_trigger ()
>     RETURNS TRIGGER
>     LANGUAGE plpgsql
>     AS
>     $BODY$
>     BEGIN
>     INSERT INTO _tmp_test1_changes (id, changes) VALUES (NEW.id,
>     hstore(OLD) - hstore(NEW));
>     RETURN NEW;
>     END
>     $BODY$;
> 
>     CREATE TRIGGER table_update AFTER INSERT OR UPDATE ON _tmp_test1
>     FOR EACH ROW EXECUTE PROCEDURE test1_trigger();____
> 
>     __ __
> 
>     INSERT INTO _tmp_test1 (val) VALUES (5);____
> 
>     ERROR:  record "old" is not assigned yet____
> 
>     DETAIL:  The tuple structure of a not-yet-assigned record is
>     indeterminate.____
> 
>     CONTEXT:  SQL statement "INSERT INTO _tmp_test1_changes (id,
>     changes) VALUES (NEW.id, hstore(OLD) - hstore(NEW))"____
> 
>     PL/pgSQL function test1_trigger() line 3 at SQL statement____
> 
>     __ __
> 
>     I couldn't find anything about this in the release notes
>     (https://www.postgresql.org/docs/11/release-11.html), but maybe I
>     just didn't know what to look for.____
> 
>     __ __
> 
>     *I doubt that this works on any PG version for INSERT.____*
> 
>     *__ __*
> 
>     *According to the documentation:____*
> 
>     *__ __*
> 
>     *https://www.postgresql.org/docs/10/plpgsql-trigger.html and
>     https://www.postgresql.org/docs/11/plpgsql-trigger.html____*
> 
>     *__ __*
> 
>     *OLD: **Data type **RECORD**; variable holding the old database row
>     for **UPDATE**/**DELETE**operations in row-level triggers. This
>     variable is unassigned in statement-level triggers and for
>     **INSERT**operations.**____*
> 
>     *__ __*
> 
>     *Regards____*
> 
>     *Charles____*
> 


-- 
Adrian Klaver
adrian.klaver@aklaver.com