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From: "Josh Berkus" <josh@agliodbs.com>
Subject: Re: Rules and Triggers
To: Ludwig Lim <lud_nowhere_man@yahoo.com>, pgsql-sql@postgresql.org
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Date: Thu, 16 May 2002 08:12:26 -0700
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Ludwig,

>   I tried converting the rule to function & trigger
> and it reported that it used an Index scan given the
> same INSERT statement.
> 
>    I was wondering why the rule used sequentail scan
> and the equivalent function trigger used index scan.

This is one of the documented differences between rules and triggers
(at least, I've seen it in the documentation *somewhere*).  I can't
tell you "why", though ... hopefully Tom or Bruce will speak to that.

For myself, I use triggers for most things, and rules just for
updatable views.  Aside for index efficiency, rules are a Postgres-only
thing, whereas several RDBMS's support triggers.   Gives me marginally
better portability.

-Josh Berkus