Message-ID: <3E688AE5.5714092D@rodos.fzk.de>
Date: Fri, 07 Mar 2003 13:04:54 +0100
From: Christoph Haller <ch@rodos.fzk.de>
MIME-Version: 1.0
To: pgsql-sql@postgresql.org
Cc: Andreas.Pflug@web.de
Subject: Re: How to notice column changes in trigger
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>
> How can I detect whether a column was changed by an update command
> inside a trigger?
>
> create table test(a int, b int, c int, primary key(a))
>
> b and c should be updated inside an update trigger if not modified by
> the statement itself
>
> 1) update test set a=0 -> trigger does its work
> 2) update test set a=0, b=1, c=2 -> trigger does nothing
> 3) update test set a=0, b=b, c=c -> trigger does nothing, but content
of
> a and b dont change either although touched
>
> What I'm looking for is something like
> IF NOT COLUMN_TOUCHED(b) THEN ...
> For MSSQL, this would be coded as  IF NOT UPDATE(b) ..
>
> IF OLD.b=NEW.b will not work, case 3) will falsely execute the trigger
code.
>
Sorry, but I don't get it.
Does
> b and c should be updated inside an update trigger if not modified by
> the statement itself
mean b=b not modified, b=1 modified even if b was 1 before ?

So you want the trigger executed only if assignments to b and/or c do
not appear within the update command. Right?

Regards, Christoph