Message-ID: <3DF4C0B4.68BA54B9@nsd.ca>
Date: Mon, 09 Dec 2002 11:11:32 -0500
From: Jean-Luc Lachance <jllachan@nsd.ca>
MIME-Version: 1.0
To: josh@agliodbs.com
Cc: Bruce Momjian <pgman@candle.pha.pa.us>,
	pgsql-sql <pgsql-sql@postgresql.org>
Subject: Re: Rules/Trigges Trade-offs
References: <200212061634.gB6GYbt02565@candle.pha.pa.us>
	<200212061525.49284.josh@agliodbs.com>
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit

Josh,

Thanks for the info.  

I need to change an insert into an update when the key already exists.
I have been using a rules to test it on a small set (table) and it
works.
"Rules can't use indexes" just scared me. I will have to test on a
larger set.
Also, I had the impression that if a trigger returned NULL, one would
get the equivalent of "DO NOTHING".
Am I wrong with that assumption?

JLL

 

Josh Berkus wrote:
> 
> Bruce, Richard,
> 
> > Triggers are mostly for testing/modifying the row being
> > inserted/updated, while rules are better for affecting other rows or
> > other tables.
> 
> Hmmm.  Thought that there were also some other criteria:
> 
> 1) Rules can't use indexes to do their processing, so Rules which query large
> secondary tables can be a bad idea (maybe this has changed?)
> 
> 2) Only Rules can "DO INSTEAD"; thus, only Rules are good for defining
> Read/Write views.
> 
> 3) There are no AFTER Rules, making, for example, a rule with a table check on
> the new data impractical, so you'd want to use Triggers or Constraints
> 
> etc.
> 
> There are, IMHO, some things Rules are better for, and some things Triggers
> are better for.   I tend to use all Triggers except for updatable views,
> simply because using a mix of Rules and Triggers can be very hard to keep
> track of, but YMMV.
> 
> --
> -Josh Berkus
>  Aglio Database Solutions
>  San Francisco