Re: Schema variables - new implementation for Postgres 15

so 25. 5. 2024 v 3:29 odesílatel Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> napsal:

> Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> writes:
> > we can introduce special safe mode started by
> > set enable_direct_variable_read to off;
> > and allowing access to variables only by usage dedicated function
> > (supported by parser) named like variable or pg_variable
>
> Didn't we learn twenty years ago that GUCs that change query
> semantics are an awful idea? Pick a single access method
> for these things and stick to it.
>

I don't think the proposed GUC exactly changes query semantics - it is
equivalent of plpgsql options: plpgsql_extra_xxxx or #variable_conflict. It
allows us to identify broken queries. And for tools that generates queries
is not problem to wrap reading variable by special pseudo function. The
code where pseudo function will be used should to work with active or
inactive strict mode (related to possibility to use variables).

Sure there is more possibilities, but I don't want to lost the possibility
to write code like

CREATE TEMP VARIABLE _x;

LET _x = 'hello';

DO $$
BEGIN
RAISE NOTICE '%', _x;
END;
$$;

So I am searching for a way to do it safely, but still intuitive and user
friendly.

Regards

Pavel

>
> regards, tom lane
>