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@xxxxxxxxxxxx> 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@xxxxxxxxx> To: "oracle-l" <oracle-l@xxxxxxxxxxxxx> Sent: Saturday, January 27, 2007 5:48 AM Subject: The Case Against Compound/Natural Keys
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