Date: Wed, 5 Nov 2025 09:24:50 +0000 (GMT)
From: PALAYRET Jacques <jacques.palayret@meteo.fr>
To: Laurenz Albe <laurenz.albe@cybertec.at>, Tom Lane <tgl@sss.pgh.pa.us>, 
	Dominique Devienne <ddevienne@gmail.com>
Cc: pgsql-general@lists.postgresql.org
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Subject: Re: PostgreSQL  trigger how to detect a column value explicitely
 modified
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Thread-Topic: PostgreSQL trigger how to detect a column value explicitely modified
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Hello,

I think you knew that I don't really want to create a function in language =
C to handle and test the values of the columns in the SQL query. For me, it=
 is much easier to use the solution of the trigger " BEFORE|AFTER UPDATE OF=
 col ".
Joke aside, I hadn't thought of that ; it is an excellent idea (simple solu=
tion).
I tested it ; it works as expected.

Thanks to people who replied.
Regards.

----- Mail original -----
De: "Laurenz Albe" <laurenz.albe@cybertec.at>
=C3=80: "PALAYRET Jacques" <jacques.palayret@meteo.fr>, pgsql-general@lists=
.postgresql.org
Envoy=C3=A9: Mardi 4 Novembre 2025 18:29:05
Objet: Re: PostgreSQL  trigger how to detect a column value explicitely mod=
ified

On Tue, 2025-11-04 at 12:48 +0000, PALAYRET Jacques wrote:
> In a trigger body, is there a simple way to know if a column value has be=
en explicitely modified ?
> Explicitely modified ; in others words, typically indicated in the SET cl=
ause of the UPDATE.
> A simple way ; I mean without analysing the SQL statement which can be ve=
ry difficult according to the statement.

Unless you want to write a C trigger function you can use

  CREATE TRIGGER ... BEFORE|AFTER UPDATE OF col ON tab FOR EACH ROW ...

Then the trigger function will only be called if the SET clause of UPDATE
contains the column "col".

Yours,
Laurenz Albe