Re: Composite Indexes with a function and a column

Thanks a lot!

From documentation:

"
IMMUTABLE indicates that the function cannot modify the database and always
returns the same result when given the same argument values; that is, it
does not do database lookups or otherwise use information not directly
present in its argument list. If this option is given, any call of the
function with all-constant arguments can be immediately replaced with the
function value.
"

I understand that to be immutable a function should not access mutable data.

If my function access another table that I have guarantee that it will not
be changed, It's safe to turn that function immutable and use in an index?
I know that i'll be punished if my guarantee fails...

Regards,

On Fri, Dec 21, 2012 at 10:12 AM, Christian Hammers <ch(at)lathspell(dot)de> wrote:

> Hello
>
> On Fri, 21 Dec 2012 08:46:14 -0200
> Alex Pires de Camargo <acamargo(at)gmail(dot)com> wrote:
>
> > Is it possible?
> >
> > Thanks!
>
> Why not?
>
> devel_np=# CREATE TABLE t (i int);
> CREATE TABLE
>
> devel_np=# CREATE INDEX ON t (length(i::text), i);
> CREATE INDEX
>
> bye,
>
> -christian-
>

--
Alex
acamargo(at)gmail(dot)com
"Por que, no mundo, os maus, tão frequentemente, sobrepujam os bons em
influência?
-Pela fraqueza dos bons; Os maus são intrigantes e audaciosos, os bons são
tímidos. Quando estes o quiserem, dominarão." -- Livro dos Espíritos, Q932.
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