Re: Patch to add functionality to specify ORDER BY in CREATE FUNCTION for SRFs
| От | Ashutosh Bapat |
|---|---|
| Тема | Re: Patch to add functionality to specify ORDER BY in CREATE FUNCTION for SRFs |
| Дата | |
| Msg-id | CAFjFpRdF776cuv-D8UxqSVzaUU7vikybzLjr4r=qccotsYkw2g@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: Patch to add functionality to specify ORDER BY in CREATE FUNCTION for SRFs (Jim Nasby <Jim.Nasby@BlueTreble.com>) |
| Список | pgsql-hackers |
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().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)
On Wed, Jan 7, 2015 at 5:03 AM, Jim Nasby <Jim.Nasby@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
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company
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