Re: new stored procedure with OUT parameters

ne 16. 12. 2018 v 20:33 odesílatel Anton Shen <4175george(at)gmail(dot)com> napsal:

> Thanks for the thoughts. The part I'm missing is that why procedures with
> OUT param 'will not be called from SQL environments'?
>

PostgreSQL, Oracle has function/procedure overloading. The function
signature - that is unique for any function is composed from all parameters
(on Oracle) or from only IN parameters (on PostgreSQL).

On Oracle I can have a procedures P(IN int, OUT varchar2), P(IN int, OUT
number) - it is not possible on Postgres, because OUT parameters are not
part of signature there. There is some workaround with passing fake
variable like P(IN int, IN varchar, OUT varchar), P(IN int, IN numeric, OUT
numeric). It is not nice, but there is not any hope to fix it due ensuring
compatibility.

The procedures are new - and now, there are time to define behave. You can
see, so INOUT parameters are passed to procedure similar to Oracle.

Because Peter didn't allow OUT variables, then he didn't need to solve a
question what parameters are part of signature. IN, INOUT parameters are
from signature perspective IN parameters - so it is nothing new.

SQL environment has not any variables (now). So you cannot to use any OUT
parameter from this environment - and then has not sense to use signature
with OUT parameters. But it is possible from PL/pgSQL - and it is not
consistent.

> Thanks,
> Anton
>
> On Sat, Dec 15, 2018 at 10:03 AM Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
> wrote:
>
>> Hi
>>
>> út 11. 12. 2018 v 7:20 odesílatel Anton Shen <4175george(at)gmail(dot)com>
>> napsal:
>>
>>> Hi all,
>>>
>>> I was playing around with the stored procedure support in v11 and found
>>> that pure OUT parameters are not supported. Is there any reason we only
>>> support INOUT but not OUT parameters?
>>>
>>
>> The procedure implementation in v11 is initial stage - only functionality
>> with some simple implementation or without design issues was implemented.
>>
>> If I remember there was not clean what is correct and expected behave of
>> usage of OUT variable when it is called from SQL environment, and when it
>> is called from plpgsql.
>>
>> On Oracle - the OUT variables are part of procedure signature - you can
>> write procedures P1(OUT a int), P1(OUT a text). Currently we have not a
>> variables in SQL environment. So if Peter implemented OUT variables now then
>>
>> a) only IN parameters will be part of signature - like functions - but it
>> is different than on Oracle, and we lost a possibility to use interesting
>> feature
>> b) the procedures with OUT variables will not be callable from SQL
>> environment - that be messy for users.
>> c) disallow it.
>>
>> I hope so PostgreSQL 12 will have schema variables, and then we can
>> implement OUT variables. Now, it is not possible (do it most correct) due
>> missing some other feature. INOUT parameters are good enough, and we have
>> opened door for future correct design.
>>
>> Regards
>>
>> Pavel
>>
>>
>>
>>>
>>> psql (11.0 (Homebrew petere/postgresql))
>>> dev=# CREATE PROCEDURE test_sp(a OUT int) LANGUAGE plpgsql AS $$
>>> dev$# BEGIN
>>> dev$# a = 5;
>>> dev$# END; $$;
>>> ERROR: procedures cannot have OUT arguments
>>> HINT: INOUT arguments are permitted.
>>>
>>> Thanks,
>>> Anton
>>>
>>