Outer Joins are Evil?

From: Barr, Stephen <Stephen.Barr_at_bskyb.com>
Date: Tue, 31 Aug 2004 16:04:10 +0100
Message-ID: <B116C5C7C606D311B54D0008C75B99201576A963@sssl_exch_usr3.sssl.bskyb.com>

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

The reasons given for this seem to be -

Simplifies user navigation of the structures - i.e. avoids outer joins.
Outer joins are slow and should be avoided at all costs.
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.

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.

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

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

Thanks,

Steve.

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Received on Tue Aug 31 2004 - 10:01:50 CDT