The following bug has been logged online:

Bug reference: 1784
Logged by: Giacomo G
Email address: matic999 (AT) hotmail (DOT) com
PostgreSQL version: 8.0.3
Operating system: linux kernel 2.6.12.2
Description: "adding missing FROM-clause" when not needed
Details:

If I populate the database with this two tables:

CREATE TABLE bar ( c varchar, d varchar);
CREATE TABLE foo ( a varchar, b varchar);
COPY bar (c, d) FROM stdin;
1 ghi
2 jkl
\.
COPY foo (a, b) FROM stdin;
1 abc
2 def
\.

When I run this select I get the output I expect:

test=# select * from foo t0 join bar t1 on ( t0.a = t1.c ) where t0.a = 1;
a | b | c | d
---+-----+---+-----
1 | abc | 1 | ghi
(1 row)


But, when i run the same query with the real name of table in the where
statement I get this:

test=# select * from foo t0 join bar t1 on ( t0.a = t1.c ) where foo.a = 1;
NOTICE: adding missing FROM-clause entry for table "foo"
a | b | c | d
---+-----+---+-----
1 | abc | 1 | ghi
2 | def | 2 | jkl
(2 rows)

while I expect the same result of the first query.

---------------------------(end of broadcast)---------------------------
TIP 3: Have you checked our extensive FAQ?

http://www.postgresql.org/docs/faq

On Mon, Jul 25, 2005 at 03:03:54AM +0100, Giacomo G wrote:
See the SELECT documentation:

http://www.postgresql.org/docs/8.0/s...ql-select.html

"When an alias is provided, it completely hides the actual name of
the table or function; for example given FROM foo AS f, the remainder
of the SELECT must refer to this FROM item as f not foo."

If you disable add_missing_from then you'll get an error instead
of a notice and unexpected results. Add_missing_from will be
disabled by default in PostgreSQL 8.1.

--
Michael Fuhr
http://www.fuhr.org/~mfuhr/

---------------------------(end of broadcast)---------------------------
TIP 6: explain analyze is your friend

Giacomo G wrote:
This isn't the "real name" of the table "t0". It is another reference to
table "foo", and as such should either raise an error or arrange to
alter the from-clause to make it valid (which is what happens).

In recent versions, you can disable the feature in your postgresql.conf
by setting "add_missing_from" to false. See the manuals - run-time
environment / compatibility.

--
Richard Huxton
Archonet Ltd

---------------------------(end of broadcast)---------------------------
TIP 1: if posting/reading through Usenet, please send an appropriate
subscribe-nomail command to majordomo (AT) postgresql (DOT) org so that your
message can get through to the mailing list cleanly

"Giacomo G" <matic999 (AT) hotmail (DOT) com> writes:
That is correct --- the statement is not legal per SQL spec, and the
only valid way to interpret it is to treat "foo.a" as a separate
reference to the table. See
http://www.postgresql.org/docs/8.0/s...-TABLE-ALIASES
or the SELECT reference page, which points out

alias

A substitute name for the FROM item containing the alias. An alias
is used for brevity or to eliminate ambiguity for self-joins (where
the same table is scanned multiple times). When an alias is
provided, it completely hides the actual name of the table or
function; for example given FROM foo AS f, the remainder of the
SELECT must refer to this FROM item as f not foo.

regards, tom lane

---------------------------(end of broadcast)---------------------------
TIP 1: if posting/reading through Usenet, please send an appropriate
subscribe-nomail command to majordomo (AT) postgresql (DOT) org so that your
message can get through to the mailing list cleanly