Обсуждение: Nonexistent NEW relation in some places of rules

In general, the task I'm trying to solve is to make a multiply inserts
for a table on the one only insert for a view.  It should be noted
about the method of producing these multiply rows, that they depend on
the VALUES given to that <top level> INSERT.  So, the trivialized
schema is:


create function produce (text) returns setof text
language plpgsql
as '
begin   return next $1||1;   return next $1||2;   return next $1||3;   return;
end;
';

create table a (a text);

create view b as   select a as b   from a;

create rule b as   on insert to b do instead   insert into a   select * from produce (new.b);


And I get
       psql:zhoppa.sql:21: ERROR:  Relation "*NEW*" does not exist

when I feed this to psql...

So, what is wrong in using NEW right from the FROM?

Thanks in advance.

Denis Zaitsev <zzz@anda.ru> writes:
> create rule b as
>     on insert to b do instead
>     insert into a
>     select * from produce (new.b);
> ERROR:  Relation "*NEW*" does not exist

> So, what is wrong in using NEW right from the FROM?

CVS tip gives a possibly more helpful error message:

ERROR:  function expression in FROM may not refer to other relations of same query level

The problem is that the rule gets expanded into something rather like
insert into a select ... from new, produce(new.b);

and we can't support that.  If we ever add support for SQL99's
LATERAL(), it might help improve matters.
        regards, tom lane

On Tue, Jul 29, 2003 at 06:32:44PM -0400, Tom Lane wrote:
> The problem is that the rule gets expanded into something rather like
> 
>     insert into a select ... from new, produce(new.b);
> 
> and we can't support that.  If we ever add support for SQL99's
> LATERAL(), it might help improve matters.

Thanks.  I was suspecting something like.  Does the presence of this
leak mean that such a selects are needed very rarely?  Or does it mean
that some well-known workaround exists?