RE: Outer Joins are Evil?

From: Cary Millsap <cary.millsap_at_hotsos.com>
Date: Tue, 31 Aug 2004 10:23:20 -0500
Message-ID: <047a01c48f6e$75cb9fb0$6701a8c0@CVMLAP02>

I don't think the SQL developer gets a choice. It's like telling a C programmer to avoid multiplication and division because they're slower = than
addition and subtraction! Once the data design is set, if the developer = has
to use outer joins to get the correct answer, then it's a choice of = either
(a)=A0use outer joins, or (b)=A0get the wrong answer.

>From the data /designer's/ perspective, I think I agree with the points you're listing below. It's probably a Very Good Idea to create data = designs
that allow your business functions to take place without outer joins.

I'll defer to Lex and others for a more definitive response.

Cary Millsap
Hotsos Enterprises, Ltd.
http://www.hotsos.com
* Nullius in verba *

Upcoming events:
- Performance Diagnosis 101: 9/14 San Francisco, 10/5 Charlotte, 10/26 Toronto
- SQL Optimization 101: 8/16 Minneapolis, 9/20 Hartford, 10/18 New = Orleans
- Hotsos Symposium 2005: March 6-10 Dallas - Visit www.hotsos.com for schedule details...

-----Original Message-----
From: oracle-l-bounce_at_freelists.org =
[mailto:oracle-l-bounce_at_freelists.org]
On Behalf Of Barr, Stephen
Sent: Tuesday, August 31, 2004 10:04 AM
To: Oracle-L_at_freelists.org
Subject: Outer Joins are Evil?

I'm currently working on a datawarehouse project (~5 Tb) where the = decision
has been made to avoid performing outer joins.
=20

The reasons given for this seem to be -
=20

1. Simplifies user navigation of the structures - i.e. avoids outer joins.=20

2.	Outer joins are slow and should be avoided at all costs.=20
3.	If an FK is missing it is populated with a default value which will

relate to an actual row in the target table, hence no rows will ever be dropped - again, supposedly this is to simply SQL and avoid outer joins. =

=20

What they actually do is populate each table in the structure with three default rows with an SK of 0, 1 & 2. Any FK's which are missing, not applicable or invalid will point to one of these rows.
=20

Now....my question is....what is so inherently evil about outer joins = that
we go to this extreme to avoid them?
=20

AND...has anyone else seen something like this deployed in other places?
=20

Thanks,
=20

Steve.
=20
=20
=20

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Received on Tue Aug 31 2004 - 10:21:50 CDT