Not in all cases
postgres=# create function non_im_immutable_function() returns float as $$
begin
return *random()*;
end;
$$ language plpgsql *immutable*;
CREATE FUNCTION
postgres=# select proname, provolatile from pg_proc where proname =
'random' or proname = 'non_im_immutable_function';
proname | provolatile
---------------------------+-------------
random | v
non_im_immutable_function | i
postgres=# select non_im_immutable_function();
non_im_immutable_function
---------------------------
0.963812265079468
(1 row)
postgres=# select non_im_immutable_function();
non_im_immutable_function
---------------------------
0.362834882922471
(1 row)
Per definition of immutable functions, the function's output shouldn't
depend upon a volatile function e.g. random().
On Wed, Jan 7, 2015 at 5:03 AM, Jim Nasby <jim.na...@bluetreble.com> wrote:
> On 1/6/15, 1:00 AM, Ashutosh Bapat wrote:
>
>>
>> Even checking whether the output of the function is in the right order or
>> not, has its cost. I am suggesting that we can eliminate this cost as well.
>> For example, PostgreSQL does not check whether a function is really
>> immutable or not.
>>
>
> Actually, it does:
>
> select test();
> ERROR: UPDATE is not allowed in a non-volatile function
> CONTEXT: SQL statement "UPDATE i SET i=i+1"
> PL/pgSQL function test() line 3 at SQL statement
> STATEMENT: select test();
> ERROR: UPDATE is not allowed in a non-volatile function
> CONTEXT: SQL statement "UPDATE i SET i=i+1"
> PL/pgSQL function test() line 3 at SQL statement
>
>
> --
> Jim Nasby, Data Architect, Blue Treble Consulting
> Data in Trouble? Get it in Treble! http://BlueTreble.com
>
--
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company
