Thread: JOINing subselects in FROM?

Hello:

I'm playing around with the syntax of the SELECT.

I have a very simple table (this is a silly example):

create table datos (año int, mes text, valor int);

with a couple tuples:

insert into datos (año, mes, valor) values (1999, 'enero', 100);
insert into datos (año, mes, valor) values (2000, 'enero', 200);
insert into datos (año, mes, valor) values (1999, 'febrero', 300);

I'm trying to JOIN two subselects-in-from clauses and can't get it
right:

SELECT foo1.mes, valor1999 AS "1999", valor2000 AS "2000" FROM
    (SELECT valor AS valor1999, mes FROM datos WHERE año=1999) AS foo1
    OUTER JOIN
        (SELECT valor AS valor2000, mes FROM datos WHERE año=2000) AS foo2
    ON foo1.mes=foo2.mes;
ERROR:  parser: parse error at or near "OUTER"

If I try to do an INNER JOIN, I get instead
SELECT foo1.mes, valor1999 AS "1999", valor2000 AS "2000" FROM
    (SELECT valor AS valor1999, mes FROM datos WHERE año=1999) AS foo1
    INNER JOIN
        (SELECT valor AS valor2000, mes FROM datos WHERE año=2000) AS foo2
    ON foo1.mes=foo2.mes;
ERROR:  flatten_join_alias_var: unexpected subtree type

But if I do it like
SELECT foo1.mes, valor1999 AS "1999", valor2000 AS "2000" FROM
        (SELECT valor AS valor1999, mes FROM datos WHERE año=1999) AS foo1,
        (SELECT valor AS valor2000, mes FROM datos WHERE año=2000) AS foo2
  WHERE foo1.mes=foo2.mes;

it works (but I lose some tuples -- I expected to get NULL there in the
OUTER JOIN query).


Remember, this is a silly example, I'm not trying to use it for anything
but playing around with the syntax. But I wonder whether this is
supposed to work?

alvherre=> select version();
                            version
----------------------------------------------------------------
 PostgreSQL 7.3devel on i686-pc-linux-gnu, compiled by GCC 2.96
(1 row)


On a related note, psql's "\h select" shows the syntax for select, but
it doesn't specify what are the terminal symbols for the join_type
non-terminal.

(this is a week-old or so CVS)

--
Alvaro Herrera (<alvherre[a]atentus.com>)
"Puedes vivir solo una vez, pero si lo haces bien, una vez es suficiente"

Alvaro Herrera <alvherre@atentus.com> writes:
> I'm trying to JOIN two subselects-in-from clauses and can't get it
> right:

> SELECT foo1.mes, valor1999 AS "1999", valor2000 AS "2000" FROM
>     (SELECT valor AS valor1999, mes FROM datos WHERE a�o=1999) AS foo1
>     OUTER JOIN
>         (SELECT valor AS valor2000, mes FROM datos WHERE a�o=2000) AS foo2
>     ON foo1.mes=foo2.mes;
> ERROR:  parser: parse error at or near "OUTER"

Should be LEFT JOIN or LEFT OUTER JOIN.

> If I try to do an INNER JOIN, I get instead
> SELECT foo1.mes, valor1999 AS "1999", valor2000 AS "2000" FROM
>     (SELECT valor AS valor1999, mes FROM datos WHERE a�o=1999) AS foo1
>     INNER JOIN
>         (SELECT valor AS valor2000, mes FROM datos WHERE a�o=2000) AS foo2
>     ON foo1.mes=foo2.mes;
> ERROR:  flatten_join_alias_var: unexpected subtree type

[ scratches head ... ]  I do not get that.  I think there must be
something broken about your build; or perhaps there's a portability
problem lurking in devel sources.  Would you try a full rebuild (make
distclean, configure, build, initdb) to eliminate the possibility of
internal version mismatches?

            regards, tom lane

En Wed, 10 Apr 2002 11:02:08 -0400
Tom Lane <tgl@sss.pgh.pa.us> escribió:

> Alvaro Herrera <alvherre@atentus.com> writes:
> > I'm trying to JOIN two subselects-in-from clauses and can't get it
> > right:
>
> > SELECT foo1.mes, valor1999 AS "1999", valor2000 AS "2000" FROM
> >     (SELECT valor AS valor1999, mes FROM datos WHERE año=1999) AS foo1
> >     OUTER JOIN
> >         (SELECT valor AS valor2000, mes FROM datos WHERE año=2000) AS foo2
> >     ON foo1.mes=foo2.mes;
> > ERROR:  parser: parse error at or near "OUTER"
>
> Should be LEFT JOIN or LEFT OUTER JOIN.

Gee. Sorry. Anyway, I corrected it and got the same error that for the
other queries:

SELECT foo1.mes, valor1999 AS "1999", valor2000 AS "2000" FROM
        (SELECT valor AS valor1999, mes FROM silly WHERE año=1999) AS foo1
     LEFT OUTER JOIN
         (SELECT valor AS valor2000, mes FROM silly WHERE año=2000) AS foo2
     ON foo1.mes=foo2.mes;
ERROR:  flatten_join_alias_var: unexpected subtree type


> [ scratches head ... ]  I do not get that.  I think there must be
> something broken about your build; or perhaps there's a portability
> problem lurking in devel sources.  Would you try a full rebuild (make
> distclean, configure, build, initdb) to eliminate the possibility of
> internal version mismatches?

I just updated CVS ("CVS tip" as you call it), make distclean, initdb'd
and recreated the test scenario. I get this "unexpected subtree type"
message.

I just got CVS REL7_2_STABLE and tested there; the LEFT OUTER JOIN works
fine, as I expected in the first place. The difference seems to lie en
the changes you made to src/backend/optimizer/util/var.c, but those are
non-trivial changes and I don't grok the code.

--
Alvaro Herrera (<alvherre[a]atentus.com>)
"Estoy de acuerdo contigo en que la verdad absoluta no existe...
El problema es que tu estás mintiendo y la mentira sí existe" (G. Lama)

Alvaro Herrera <alvherre@atentus.com> writes:
> [ in development sources ]
> SELECT foo1.mes, valor1999 AS "1999", valor2000 AS "2000" FROM
>     (SELECT valor AS valor1999, mes FROM datos WHERE a�o=1999) AS foo1
>     INNER JOIN
>         (SELECT valor AS valor2000, mes FROM datos WHERE a�o=2000) AS foo2
>     ON foo1.mes=foo2.mes;
> ERROR:  flatten_join_alias_var: unexpected subtree type

I have committed changes to fix this bug.  Thanks for the report!

            regards, tom lane