Re: Schema variables - new implementation for Postgres 15
| От | Pavel Stehule |
|---|---|
| Тема | Re: Schema variables - new implementation for Postgres 15 |
| Дата | |
| Msg-id | CAFj8pRCOFzE4mOcn=mQEiCRqOKjjUiD7V3OZBnMQH9uG=y=jHg@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: Schema variables - new implementation for Postgres 15 (Peter Eisentraut <peter@eisentraut.org>) |
| Список | pgsql-hackers |
st 22. 5. 2024 v 14:37 odesílatel Peter Eisentraut <peter@eisentraut.org> napsal:
On 18.05.24 13:29, Alvaro Herrera wrote:
> I want to note that when we discussed this patch series at the dev
> meeting in FOSDEM, a sort-of conclusion was reached that we didn't want
> schema variables at all because of the fact that creating a variable
> would potentially change the meaning of queries by shadowing table
> columns. But this turns out to be incorrect: it's_variables_ that are
> shadowed by table columns, not the other way around.
But that's still bad, because seemingly unrelated schema changes can
make variables appear and disappear. For example, if you have
SELECT a, b FROM table1
and then you drop column b, maybe the above query continues to work
because there is also a variable b. Or maybe it now does different
things because b is of a different type. This all has the potential to
be very confusing.
The detection of possible conflicts works well (in or outside PL too)
create variable x as int;
create table foo(x int);
insert into foo values(110);
set session_variables_ambiguity_warning to on;
(2024-05-23 08:22:34) postgres=# do $$
begin
raise notice '%', (select x from foo);
end;
$$;
WARNING: session variable "x" is shadowed
LINE 1: (select x from foo)
^
DETAIL: Session variables can be shadowed by columns, routine's variables and routine's arguments with the same name.
QUERY: (select x from foo)
NOTICE: 110
DO
(2024-05-23 08:22:35) postgres=# do $$ declare x int default 100;
begin
raise notice '%', x;
end;
$$;
WARNING: session variable "x" is shadowed
LINE 1: x
^
DETAIL: Session variables can be shadowed by columns, routine's variables and routine's arguments with the same name.
QUERY: x
NOTICE: 100
DO
begin
raise notice '%', (select x from foo);
end;
$$;
WARNING: session variable "x" is shadowed
LINE 1: (select x from foo)
^
DETAIL: Session variables can be shadowed by columns, routine's variables and routine's arguments with the same name.
QUERY: (select x from foo)
NOTICE: 110
DO
(2024-05-23 08:22:35) postgres=# do $$ declare x int default 100;
begin
raise notice '%', x;
end;
$$;
WARNING: session variable "x" is shadowed
LINE 1: x
^
DETAIL: Session variables can be shadowed by columns, routine's variables and routine's arguments with the same name.
QUERY: x
NOTICE: 100
DO
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