Re: Is it This Join Condition Do-Able?

How about:

SELECT a.keyfld, a.foo1, b.foo2, c.foo3
FROM a
LEFT JOIN b USING(keyfld)
LEFT JOIN c USING(keyfld)

Dmitri

> -----Original Message-----
> From: pgsql-sql-owner@postgresql.org
> [mailto:pgsql-sql-owner@postgresql.org] On Behalf Of Lane Van Ingen
> Sent: Wednesday, August 17, 2005 12:55 PM
> To: pgsql-sql@postgresql.org
> Subject: [SQL] Is it This Join Condition Do-Able?
>
>
> 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.
>
> select a.keyfld, a.foo1, b.foo2, c.foo3
> from a, b, c
> where a.keyfld = <some value>
> and   a.keyfld = b.keyfld
> and   a.keyfld = c.keyfld;
>
> Results could look like this:
>   a.keyfld  a.foo1   b.foo2  c.foo3
>     xxxx     xxxx     xxxx    (null)
>     xxxx     xxxx    (null)    xxxx
>     xxxx     xxxx    (null)   (null)
>     xxxx     xxxx     xxxx     xxxx
>
>
>
> ---------------------------(end of
> broadcast)---------------------------
> TIP 9: In versions below 8.0, the planner will ignore your desire to
>        choose an index scan if your joining column's datatypes do not
>        match
>
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