Could you please stop to send these message?
От | Xue-Feng Yang |
---|---|
Тема | Could you please stop to send these message? |
Дата | |
Msg-id | 20030312223348.56565.qmail@web41604.mail.yahoo.com обсуждение исходный текст |
Ответ на | Re: Using functions as filters in queries (Xue-Feng Yang <just4look@yahoo.com>) |
Список | pgsql-admin |
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: > Could you please stop to send these message? > > > --- 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 > > ______________________________________________________________________ > > Post your free ad now! http://personals.yahoo.ca > > ---------------------------(end of > broadcast)--------------------------- > TIP 3: if posting/reading through Usenet, please > send an appropriate > subscribe-nomail command to majordomo@postgresql.org > so that your > message can get through to the mailing list cleanly ______________________________________________________________________ Post your free ad now! http://personals.yahoo.ca
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