Should be easy enough to get this result (or is it possible?)...

Sean Chittenden <sean@chittenden.org> writes:

The upshot of things being that I want the 2nd query below (f.foo =3D
'b') to return foo_id and foo. Am I missing something?

I'm not real clear on what you're after, but the query results look
correct. The LEFT JOIN result (without any WHERE restriction) is

test=# SELECT f.foo_id, f.foo, b.bar_id, b.bar
test-# FROM foo AS f LEFT JOIN bar AS b on (f.foo_id = b.foo_id);
foo_id | foo | bar_id | bar
--------+-----+--------+-----
1 | a | 2 | y
1 | a | 1 | x
1 | a | 3 | z
2 | b | 4 | x
2 | b | 5 | z
3 | c | |
(6 rows)

and so the restricted outputs with the WHERE clauses look right.
What were you trying to do exactly?

regards, tom lane

On Wed, 15 May 2002, Sean Chittenden wrote:

I think the following code explains my problem more elegantly than I
could ever hope to try and explain in a reasonable amount of words.
The upshot of things being that I want the 2nd query below (f.foo =
'b') to return foo_id and foo. Am I missing something? My head
stands poised to get clobbered with the clue-bat. Here's the test
case:

CREATE TABLE foo ( foo_id SERIAL NOT NULL, foo VARCHAR(32) NOT NULL );
CREATE TABLE bar ( bar_id SERIAL NOT NULL, foo_id INT NOT NULL, bar VARCHAR(32) NOT NULL);
INSERT INTO foo (foo) VALUES ('a');
INSERT INTO foo (foo) VALUES ('b');
INSERT INTO foo (foo) VALUES ('c');
INSERT INTO bar (foo_id, bar) VALUES ('1','x');
INSERT INTO bar (foo_id, bar) VALUES ('1','y');
INSERT INTO bar (foo_id, bar) VALUES ('1','z');
INSERT INTO bar (foo_id, bar) VALUES ('2','x');
INSERT INTO bar (foo_id, bar) VALUES ('2','z');

SELECT f.foo_id, f.foo, b.bar_id, b.bar
FROM foo AS f LEFT JOIN bar AS b on (f.foo_id = b.foo_id)
WHERE (b.bar ISNULL OR b.bar = 'y') AND f.foo = 'b';
foo_id | foo | bar_id | bar
--------+-----+--------+-----
(0 rows)

I think you want something like (not completely tested):
SELECT f.foo_id, f.foo, b.bar_id, b.bar
from foo as f left join
(select * from bar b where b.bar='y' or b.bar is null) as b
on (f.foo_id=b.foo_id) where f.foo='b';

You want to limit the bar rows you're left joining to, not
the rows from the output of the join I think.

I think the following code explains my problem more elegantly than I
could ever hope to try and explain in a reasonable amount of words.
The upshot of things being that I want the 2nd query below (f.foo =
'b') to return foo_id and foo. Am I missing something? My head
stands poised to get clobbered with the clue-bat. Here's the test
case:

CREATE TABLE foo ( foo_id SERIAL NOT NULL, foo VARCHAR(32) NOT NULL );
CREATE TABLE bar ( bar_id SERIAL NOT NULL, foo_id INT NOT NULL, bar VARCHAR(32) NOT NULL);
INSERT INTO foo (foo) VALUES ('a');
INSERT INTO foo (foo) VALUES ('b');
INSERT INTO foo (foo) VALUES ('c');
INSERT INTO bar (foo_id, bar) VALUES ('1','x');
INSERT INTO bar (foo_id, bar) VALUES ('1','y');
INSERT INTO bar (foo_id, bar) VALUES ('1','z');
INSERT INTO bar (foo_id, bar) VALUES ('2','x');
INSERT INTO bar (foo_id, bar) VALUES ('2','z');

SELECT f.foo_id, f.foo, b.bar_id, b.bar
FROM foo AS f LEFT JOIN bar AS b on (f.foo_id = b.foo_id)
WHERE (b.bar ISNULL OR b.bar = 'y') AND f.foo = 'b';
foo_id | foo | bar_id | bar
--------+-----+--------+-----
(0 rows)

I think you want something like (not completely tested):
SELECT f.foo_id, f.foo, b.bar_id, b.bar
from foo as f left join
(select * from bar b where b.bar='y' or b.bar is null) as b
on (f.foo_id=b.foo_id) where f.foo='b';

You want to limit the bar rows you're left joining to, not
the rows from the output of the join I think.

Cha-ching! Yeah, you successfully clubbed me w/ the clue-bat: left
join on a sub-select gave me exactly what I wanted: thank you. -sc

--
Sean Chittenden