Re: Multiple-action rule surprise

On 2005-08-04, "Eugene Shekhtman" <postgre(at)xenomics(dot)com> wrote:
> PostgreSQL version: 8.0.3
> OS: Win32 (Win 2003 Server)
>
> There is something strange and counterintuitive about the way that
> multiple-action PostgreSQL rules work.

The absolute first thing you must learn about using rules in postgresql
is that _rules are not procedural logic_, i.e. you can't express them as
"if (a) then do B". Rules rewrite the command _before_ anything is
executed (indeed before anything is even planned). At the time of
rewriting, there is no way to know whether the WHERE clause of a rule will
be matched, so the rule is always expanded the same way, and the WHERE
clause becomes part of the rewritten command.

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Andrew, Supernews
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