Q: We are trying to find some theory about the benefits to have a Primary Key to identify records in a Fact Tables. We do not use it because we presume all the integrity issues are treated in ETL and the volume of Index will greatly increase the size of my DW. Do you have any specific suggestions about the use of a PK in Fact Tables? (I'm not talking about FK with dimensions.)
Chuck Kelley's Answer: You will find many different answers to this question. Personally, I would prefer to have the primary key defined on my Fact tables to make sure that the ETL is doing the job correctly. It is my opinion that the database should always be correct and I don't always trust the developers to get it right. I have seen the developers put in Distinct clauses to make them distinct before writing them out, thus dropping some data.
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