Could you please stop to send these message?
I unscripted this list a few months ago and hadn't
received messages for months.
I received messages from the list again started from
yesterday.
Could you please stop to send these message?
--- Xue-Feng Yang <just4look@yahoo.com> wrote: > >
>
> --- Stephan Szabo <sszabo@megazone23.bigpanda.com>
> wrote: >
> > On Mon, 10 Mar 2003, Chris Mungall wrote:
> >
> > > I have a problem that can be reduced to this
> > equivalent but simpler
> > > problem:
> >
> > > EXPLAIN ANALYZE select * from t where n=5 AND x
> > like 'a%';
> >
> > 5 is a constant.
> >
> > > Case 2:
> > >
> > > Now I want to replace the "n=5" clause with a
> > function:
> > >
> > > CREATE FUNCTION f(t, int) RETURNS bool AS
> > > 'SELECT $1.n = $2'
> > > LANGUAGE 'sql';
> > >
> > > EXPLAIN ANALYZE select * from t where f(t, 5)
> AND
> > x like 'a%';
> > >
> > > Now looking at the two cases (without and with
> > function) I can see that
> > > they are equivalent, but Pg treats them
> > differently. I guess it is failing
> > > to distiguish between two cases - if the
> function
> > has no FROM clause, then
> > > it is a simple case of variable substitution
> into
> > the original WHERE
> > > clause. If it does include a FROM clause, it's
> not
> > so simple and
> > > optimisation is hard, so the function becomes
> the
> > filter.
> >
> > It doesn't look at the contents of the function.
> It
> > looks at whether the
> > function is defined IMMUTABLE, STABLE or VOLATILE.
>
> > With a VOLATILE
> > function (the default), the system is not
> guaranteed
> > that given the
> > same arguments that the result is the same. You
> > might want to read
> > the description in the manpage for CREATE
> FUNCTION.
> >
> >
> >
> >
> > ---------------------------(end of
> > broadcast)---------------------------
> > TIP 4: Don't 'kill -9' the postmaster
>
>
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