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Indexing/Unique Key

Nile
9/25/2005 3:36:24 PM

sql server data warehouse: This is my first post here, hopefully you folks can help me.
I have the typical Invoice Header and Invoice Detail Fact Tables.
I’ve read that you should declare a clustered index on all of the
foreign dimension keys in a fact table (for SQL Server).
However, that wouldn’t be unique as a customer can be invoiced for the
same part on the same day, etc.. right?
So what do people typically do - declare a unique clustered index on
the Degenerate dimensions of Invoice Number and Invoice Line Number?
What is the best index to put on these fact tables?
Thanks,
Nile

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Re: Indexing/Unique Key

Peter Nolan
9/26/2005 2:55:38 PM

Nile,
there is no rule that says detail level fact tables must have the
combination of keys be unique. Though on a summary level fact table the
rule is they must be unique.

I believe you can make a non-unique clustered index on 2000 with no ill
effects.

Personally, nowadays I always create a single integer key at the front
of txn level fact tables and this is the primary key and then I just
create indexes on the columns in the fact tables as required.......I
should note that I have not built a decent sized DW on 2000.....I've
been doing this on other databases with bit mapped indexes...I did this
on 7 and it all worked ok after some coaxing......I hope to get back
into the world of building the odd reasonably sized DW on sql server in
the not too distant future...

Peter

Re: Indexing/Unique Key

Richard Kemp
9/27/2005 11:49:04 PM

[quoted text, click to view]
Peter, why bother to create a primary key on a fact table at all? Its
never used for lookup, so its a wasted index.

My $0.02

Re: Indexing/Unique Key

Peter Nolan
10/4/2005 2:54:52 AM

Hi Rick,
this was discussed at some length on dwlist
(datawarehousing.com)...many people say they see no use for a unique
key on a fact table....

However, over the last few years at some of the sites I have worked on
we have found some great uses for putting a single integer key on the
front of a fact table. We do this and use it often. (But we don't
publish what we use it for.)

Best Regards

Peter

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