Message-ID: <3E886379.618F6AE6@Yahoo.com>
Date: Mon, 31 Mar 2003 10:49:13 -0500
From: Jan Wieck <JanWieck@Yahoo.com>
Organization: Home
MIME-Version: 1.0
To: Josh Berkus <josh@agliodbs.com>
Cc: Andreas Pflug <Andreas.Pflug@web.de>, pgsql-sql@postgresql.org
Subject: Re: How to notice column changes in trigger
References: <3E6874CD.4090501@web.de> <200303070941.41276.josh@agliodbs.com>
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Josh Berkus wrote:
> 
> Andreas,
> 
> > 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
> 
> > IF OLD.b=NEW.b will not work, case 3) will falsely execute the trigger
> > code.
> 
> I still don't get why you'd want to do this.   Can you provide are real-world
> example where there is a difference between setting B=B and not updating B?

Setting b=b and not updating it is indeed identical ... at least after
the targetlist completion in PostgreSQL. But it is different from
b=<b's-old-value>, and the fact that we cannot distinguish between these
two (inside the trigger) prevents us from skipping foreign key checks if
your fk-values haven't been touched.


Jan

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