Date: Fri, 13 Mar 2020 18:56:37 -0400
From: Bruce Momjian <bruce@momjian.us>
To: mib@nic.at, pgsql-docs@lists.postgresql.org
Subject: Re: Wrong insert before trigger examples
Message-ID: <20200313225637.GB10187@momjian.us>
References: <158089540905.1098.15071165437284409576@wrigleys.postgresql.org>
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On Wed, Feb  5, 2020 at 09:36:49AM +0000, PG Doc comments form wrote:
> The following documentation comment has been logged on the website:
> 
> Page: https://www.postgresql.org/docs/12/ddl-partitioning.html
> Description:
> 
> Hi,
> 
> I just noticed that the example in 5.11.3.1. Point 5 contains an "before
> insert trigger" which will not work anymore (I think since Postgres 12).
> This trigger is not needed anymore and causes an error message.

Sorry for the delay in replying.  I was able to successfully create the
trigger:

	CREATE TABLE measurement (
	    city_id         int not null,
	    logdate         date not null,
	    peaktemp        int,
	    unitsales       int
	);

	CREATE TABLE measurement_y2006m02 (
	    CHECK ( logdate >= DATE '2006-02-01' AND logdate < DATE '2006-03-01' )
	) INHERITS (measurement);

	CREATE INDEX measurement_y2006m02_logdate ON measurement_y2006m02 (logdate);

	CREATE OR REPLACE FUNCTION measurement_insert_trigger()
	RETURNS TRIGGER AS $$
	BEGIN
	    INSERT INTO measurement_y2008m01 VALUES (NEW.*);
	    RETURN NULL;
	END;
	$$
	LANGUAGE plpgsql;

	CREATE TRIGGER insert_measurement_trigger
	    BEFORE INSERT ON measurement
	    FOR EACH ROW EXECUTE FUNCTION measurement_insert_trigger();

There are actually two definitions of 'measurement' in the docs above,
and you might have used the partitioned one:

	CREATE TABLE measurement (
	    city_id         int not null,
	    logdate         date not null,
	    peaktemp        int,
	    unitsales       int
	) PARTITION BY RANGE (logdate);

I have developed the attached patch to clarify which definition to use. 
I am not sure if more extensive changes are needed.

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EnterpriseDB                             https://enterprisedb.com

+ As you are, so once was I.  As I am, so you will be. +
+                      Ancient Roman grave inscription +

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diff --git a/doc/src/sgml/ddl.sgml b/doc/src/sgml/ddl.sgml
index 8d3a0d1c22..d2588876c0 100644
--- a/doc/src/sgml/ddl.sgml
+++ b/doc/src/sgml/ddl.sgml
@@ -4103,8 +4103,8 @@ ALTER INDEX measurement_city_id_logdate_key
      <title>Example</title>
 
      <para>
-      We use the same <structname>measurement</structname> table we used
-      above.  To implement partitioning using inheritance, use
+      We use the non-partitioned <structname>measurement</structname>
+      table above.  To implement partitioning using inheritance, use
       the following steps:
 
       <orderedlist spacing="compact">

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