Re: new stored procedure with OUT parameters - Mailing list pgsql-general

On 12/16/18 11:33 AM, Anton Shen wrote:
> Thanks for the thoughts. The part I'm missing is that why procedures 
> with OUT param 'will not be called from SQL environments'?

Pretty sure Pavel was referring to:

https://www.postgresql.org/docs/11/xfunc-sql.html#XFUNC-OUTPUT-PARAMETERS

"Notice that output parameters are not included in the calling argument 
list when invoking such a function from SQL. This is because PostgreSQL 
considers only the input parameters to define the function's calling 
signature. ..."


 From this commit:

https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=e4128ee767df3c8c715eb08f8977647ae49dfb59

"SQL procedures

This adds a new object type "procedure" that is similar to a function
but does not have a return type and is invoked by the new CALL statement
instead of SELECT or similar.
...

While this commit is mainly syntax sugar around existing functionality,
future features will rely on having procedures as a separate object
type."

I read this to mean that since SQL functions don't have OUT in the 
signature at this time, SQL procedures do not either.

> 
> Thanks,
> Anton
> 
> On Sat, Dec 15, 2018 at 10:03 AM Pavel Stehule <pavel.stehule@gmail.com 
> <mailto:pavel.stehule@gmail.com>> wrote:
> 
>     Hi
> 
>     út 11. 12. 2018 v 7:20 odesílatel Anton Shen <4175george@gmail.com
>     <mailto:4175george@gmail.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
> 


-- 
Adrian Klaver
adrian.klaver@aklaver.com