Re: RULE vs. SEQUENCE

Karel Zak wrote:
> > > But executor can knows that somethig was already executed, we can mark
> > > some already executed expressions in rewriter and not execute it again in
> > > final executor... like:
> > ...
> > >
> > > IMHO this is a good point for 7.2 ...
> >
> > But if instead of nextval() you had random(), would you still want to execute
> > it
> > only once ? And how should postgres know ?
>
> Talking you still about RULEs?

Yes, he is.

>
> ...I don't undestand you. What is a 'NEW' in RULE? I (and probably more
> users) expect that new data from tuple which go into original table. Right?

Most people would expect that - but it is the targetlist
expression of this column from the query which fired the
rule! That's a little difference.

> Not ... if you use sequence. IMHO it's not "feature" but nice bug that
> crash your data integrity...

The PostgreSQL rule system is based on a general productional
query rewrite rule system, designed decades ago without
thinking about column values like nextval() or random(). The
usage of those expressions in a query firing rules leads to
unpredictable results.

To understand how rules work in detail you should read
chapter 8 of the programmers manual.

Jan

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