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Date: Thu, 25 Mar 2010 17:26:13 +0100
Message-ID: <162867791003250926v4230f599u13f82d3a56ffd877@mail.gmail.com>
Subject: Re: Does IMMUTABLE property propagate?
From: Pavel Stehule <pavel.stehule@gmail.com>
To: pgsql-sql@postgresql.org
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2010/3/25 Louis-David Mitterrand <vindex+lists-pgsql-sql@apartia.org>:
> On Thu, Mar 25, 2010 at 08:27:27AM +0100, Pavel Stehule wrote:
>> 2010/3/25 Louis-David Mitterrand <vindex+lists-pgsql-sql@apartia.org>:
>> > On Sat, Mar 06, 2010 at 04:31:55PM -0500, Tom Lane wrote:
>> >> Petru Ghita <petrutz@venaver.info> writes:
>> >> > "..immediately replaced with the function value" doesn't mean that =
the
>> >> > results of a previously evaluated function for the same parameters =
are
>> >> > stored and reused?
>> >>
>> >> No, it means what it says: the function is executed once and replaced
>> >> with a constant representing the result value.
>> >
>> > So for example a function like:
>> >
>> >
>> > =C2=A0 =C2=A0 =C2=A0 =C2=A0CREATE OR REPLACE FUNCTION shorten_cruise_t=
ype(intext text) RETURNS text
>> > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0AS $$
>> > =C2=A0 =C2=A0 =C2=A0 =C2=A0declare
>> > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0outtext text;
>> > =C2=A0 =C2=A0 =C2=A0 =C2=A0begin
>> > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0outtext =3D tri=
m(regexp_replace(intext, E'\\s*Short( Break)?', '', 'i'));
>> > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0return outtext;
>> > =C2=A0 =C2=A0 =C2=A0 =C2=A0end;
>> > =C2=A0 =C2=A0 =C2=A0 =C2=A0$$
>> > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0LANGUAGE plpgsq=
l;
>> >
>>
>> yes it should be declared as immutable. plpgsql function is black box
>> for executor, so you have to use some flag. language sql is different,
>> executor see inside, so there you can not do it.
>
> Hmm, that's interesting. So for simple functions (like my example) it is
> better to write them in plain sql? And in that case no 'immutable' flag
> is necessary?
>

sure

Pavel

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