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RE: The Case Against Compound/Natural Keys

From: Bobak, Mark <>
Date: Mon, 29 Jan 2007 10:34:46 -0500
Message-ID: <>

I guess I'm a little late to this party.

FYI, Steve Adams has a nice write up on his website of synthetic vs. natural keys:


Mark J. Bobak
Senior Oracle Architect
ProQuest Information & Learning

There is nothing so useless as doing efficiently that which shouldn't be
done at all.  -Peter F. Drucker, 1909-2005

-----Original Message-----
[] On Behalf Of Don Seiler
Sent: Monday, January 29, 2007 10:23 AM
To: jaromir nemec
Cc: oracle-l
Subject: Re: The Case Against Compound/Natural Keys

My database is actually more of an all-purpose hybrid.  We have OLTP
data where data is entered by sales and updated by customer service,
etc.  We then bulk-load call records and processed billing information
(we are a telecom) that the customer service app uses when customers
call about their bills or question a call.  So we don't have fact vs
dimension tables as you might find in an ideal DW instance.

To be precise, I don't hate natural keys for the sake of hating natural
keys.  It's the composite keys that I hate, and especially when there
are no queries that such a large index would address.

These tables are already partitioned with local indexes.  We are running
the "rolling window" scenario, keeping the most recent 4 months.

Jack: are you suggesting that I put a foreign key constraint/index on
the leading X number of fields already in my primary key
constraint/index?  Because that is what it would be, and is yet another
exhibit of my frustration with this design (or lack thereof).


On 1/28/07, jaromir nemec <> wrote:

> Don,
> > These tables are bulk-loaded and .
> I assume your database is a kind of DW system.
> > They've all heard me calling for
> > surrogate keys, but they say they need uniqueness among this set of

> > fields. Then when they discover duplicates, they just add another
> > field.
> I thing you address two different problems here:
> a) how to enforce the uniqueness of a fact table
> b) how to define the primary key (natural / surrogate) on the
> dimension table
> Uniqueness of a fact table can be enforced using index, alternatively
> you may define a cleaning step in the loading process (eliminating the

> dups before the load) and not to rely on an index. A similar
> pre-processing step can enforce the consistency of the FK relation to
the parent table.
> For a dimensional table (your "parent table") there are two options in

> my opinion
> a) use natural key as a primary key of the dimension and a foreign key

> of the fact table - it is your implementation
> b) use surrogate key for PK of the dimension and FK of the fact table

> and additionally denormalize the dimension natural key into the fact
> There is a nice example on Jonathan Lewis blog demonstrating the
> consequences of using "pure" surrogates.
> When to use surrogate keys? It depends on the "nature" of the natural
> A little example: I wouldn't for sure set up a DW with natural key
> (only) for Oracle product names. Querying webDB, htmlDB, RAC,. over
> years of history would be a nightmare.
> A real value added surrogate key processing must implement some logic
> deciding when to assign a new key (for a new dimension instance) or to

> reuse existing one (for a new version of changed dimension instance).
> Jaromir D.B. Nemec
> ----- Original Message -----
> From: "Don Seiler" <>
> To: "oracle-l" <>
> Sent: Saturday, January 27, 2007 5:48 AM
> Subject: The Case Against Compound/Natural Keys
-- --
Received on Mon Jan 29 2007 - 09:34:46 CST

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