Message-ID: <3A004C68.C0F5758C@agliodbs.com>
Date: Wed, 01 Nov 2000 09:01:28 -0800
From: Josh Berkus <josh@agliodbs.com>
Reply-To: josh@agliodbs.com
Organization: Aglio Database Solutions
MIME-Version: 1.0
To: sqllist <pgsql-sql@postgresql.org>
Subject: Re: Outer Joins
References: <s9ffea47.097@eskom.co.za>
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit

Marc,

> select a.col1, b.col2 from a,b
> where a.col1 = b.col2
>    or  b.col2 is null

The above would select each record in a that matched a record in b, plus
each record in b for every possible a where b.col2 was null - not where
there was no match.

> select a.col1, b.col2 from a,b
> where a.col1 = b.col2
>    or  a.col1 not in (select b.col2 from b)

This would work, but it would be *much* slower than a UNION query.  "Not
In" queries are perhaps the slowest you can run; see the earlier thread
"Query Problem" for a discussion.  UNION queries are, in fact, very fast
... just awkward to code and manipulate.

					-Josh

-- 
______AGLIO DATABASE SOLUTIONS___________________________
                                        Josh Berkus
   Complete information technology      josh@agliodbs.com
    and data management solutions       (415) 436-9166
   for law firms, small businesses       fax  436-0137
    and non-profit organizations.       pager 338-4078
                        		San Francisco