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Date: Tue, 16 Jun 2020 12:41:08 -0400
From: Bruce Momjian <bruce@momjian.us>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: petermpallesen@gmail.com, pgsql-docs@lists.postgresql.org
Subject: Re: Not using suppress_redundant_updates_trigger in
 sql-createtrigger.html#examples
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On Tue, Jun 16, 2020 at 10:08:14AM -0400, Tom Lane wrote:
> Bruce Momjian <bruce@momjian.us> writes:
> > I have created the attached patch to mention
> > suppress_redundant_updates_trigger() in this case.  I don't think having
> > an actual example is warranted.
> 
> I don't like this patch, because in fact
> suppress_redundant_updates_trigger is entirely unrelated to the stated
> purpose of that example (namely, to log something if the table was
> changed).  The way you've written it makes it sound like
> suppress_redundant_updates_trigger could be used as an alternative
> implementation of that requirement.

Ah,  I see your point.

> If you want to mention suppress_redundant_updates_trigger somewhere
> in this area, that's fine, but it should be treated as an independent
> topic rather than being wedged into the middle of an unrelated example.
> Maybe a distinct para saying something like "To suppress no-op updates
> of a table, see suppress_redundant_updates_trigger." (and making that
> an actual link would be a good idea).

I have developed the attached patch which is in a better direction.

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

  The usefulness of a cup is in its emptiness, Bruce Lee


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diff --git a/doc/src/sgml/ref/create_trigger.sgml b/doc/src/sgml/ref/create_trigger.sgml
index 303881fcfb..7ef96c5650 100644
--- a/doc/src/sgml/ref/create_trigger.sgml
+++ b/doc/src/sgml/ref/create_trigger.sgml
@@ -454,7 +454,9 @@ UPDATE OF <replaceable>column_name1</replaceable> [, <replaceable>column_name2</
    row's contents by <literal>BEFORE UPDATE</literal> triggers are not considered.
    Conversely, a command such as <literal>UPDATE ... SET x = x ...</literal>
    will fire a trigger on column <literal>x</literal>, even though the column's
-   value did not change.
+   value did not change;  use function <link
+   linkend="functions-trigger"><function>suppress_redundant_updates_trigger</function></link>
+   in triggers to suppress non-change updates.
   </para>
 
   <para>

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