Re: problem (bug?) with "in (subquery)"

On Fri, Jul 15, 2005 at 09:59:27AM -0400, Tom Lane wrote:
> Luca Pireddu <luca(at)cs(dot)ualberta(dot)ca> writes:
> > So, am I wrong in expecting each strain record to appear only once in the
> > result set? Or is there something wrong with PostgreSQL?
>
> Could we see a self-contained example (table definitions and sample data
> as a SQL script)? I don't really have time to reverse-engineer a test
> case from your description ...

I've been reverse-engineering and simplifying this. Here's something
that I think is close:

CREATE TABLE foo (id integer);
CREATE TABLE bar (id1 integer, id2 integer);

INSERT INTO foo VALUES (1);

INSERT INTO bar VALUES (1, 1);
INSERT INTO bar VALUES (2, 2);
INSERT INTO bar VALUES (3, 1);

SELECT *
FROM foo
WHERE id IN (SELECT id2 FROM (SELECT DISTINCT id1, id2 FROM bar) AS s);
id
----
1
1
(2 rows)

SELECT *
FROM foo
WHERE id IN (SELECT id2 FROM (SELECT id1, id2 FROM bar) AS s);
id
----
1
(1 row)

8.0.3 and HEAD behave as shown. 7.4.8, 7.3.10, and 7.2.8 return a
single row for both queries.

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