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).

Don.

On 1/28/07, jaromir nemec <jaromir_at_db-nemec.com> 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 table.
> 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 keys.
> 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).
>
> HTH
>
> Jaromir D.B. Nemec
> ----- Original Message -----
> From: "Don Seiler" <don_at_seiler.us>
> To: "oracle-l" <oracle-l_at_freelists.org>
> Sent: Saturday, January 27, 2007 5:48 AM
> Subject: The Case Against Compound/Natural Keys
>
>
>
>

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