RE: Outer Joins are Evil?
- From: "Cary Millsap" <cary.millsap@xxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Tue, 31 Aug 2004 10:23:20 -0500
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@xxxxxxxxxxxxx =
[mailto:oracle-l-bounce@xxxxxxxxxxxxx]
On Behalf Of Barr, Stephen
Sent: Tuesday, August 31, 2004 10:04 AM
To: Oracle-L@xxxxxxxxxxxxx
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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