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Join Two fact tables that has different grain

Posted on 2007-12-02
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Last Modified: 2008-03-04
I have two fact tables that share the same dimension (consumer) but have different grains ..

Fact A:

Consumer_key, Episode_key, Episode_Begin_date_key,assessment_key

Fact B:
Consumer_key, Episode_key, Service_begin_date_key, Sum_of_Cost



There is 1:M relationshiop between Fact A and Fact B...

IS it a bad idea to join two fact tables to get a result ?
DO I have to always use a common dimension table , in this case, DimConsumer to join to fact tables?

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Question by:jung1975
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imitchie earned 250 total points
ID: 20391999
If some cases you have to join them together, then there's no other choice so there's no good/bad idea. However, you should reconsider alternate routes to arrive at your facts, possibly Fact C, if performance becomes an issue.
For joining, yes you do need a common dimension table.
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by:nicolasdiogo
nicolasdiogo earned 250 total points
ID: 20396038
i suppose i will have to say depends, you could use the more detailed fact to support deeper business investigations.

if you want to allow users to check customers' assessments using FACT A  and then drill through into FACT B on a second report would make sense and keep performance good.

BUT you could also amalgamate both FACTs into a single table if performance becomes an issue.

AND you will always need shared dimensions to be able to bridge between fact tables to make them work properly.


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