Re: Is it This Join Condition Do-Able?

On Wed, Aug 17, 2005 at 12:54:50PM -0400, Lane Van Ingen wrote:
> Given three tables: a, b, c ; each consist of a 'keyfld' and a field called
> 'foo':
> tbl a tbl b tbl c
> --------- --------- ---------
> a.keyfld b.keyfld c.keyfld
> a.foo1 b.foo2 c.foo3
>
> I want to always return all of tbl a; and I want to return b.foo2 and c.foo3 if
> they can be joined to based on keyfld.a; I know that it will involve a LEFT OUTER
> JOIN on table a, but have not seen any examples of joins like this on 3 or more
> tables.

Does this example do what you want?

CREATE TABLE a (keyfld integer, foo1 text);
CREATE TABLE b (keyfld integer, foo2 text);
CREATE TABLE c (keyfld integer, foo3 text);

INSERT INTO a VALUES (1, 'a1');
INSERT INTO a VALUES (2, 'a2');
INSERT INTO a VALUES (3, 'a3');
INSERT INTO a VALUES (4, 'a4');

INSERT INTO b VALUES (1, 'b1');
INSERT INTO b VALUES (4, 'b4');

INSERT INTO c VALUES (2, 'c2');
INSERT INTO c VALUES (4, 'c4');

SELECT a.keyfld, a.foo1, b.foo2, c.foo3
FROM a
LEFT OUTER JOIN b USING (keyfld)
LEFT OUTER JOIN c USING (keyfld);
keyfld | foo1 | foo2 | foo3
--------+------+------+------
1 | a1 | b1 |
2 | a2 | | c2
3 | a3 | |
4 | a4 | b4 | c4
(4 rows)

--
Michael Fuhr