Very Small Dimension Table

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Very Small Dimension Table

Post  KKumar on Wed Apr 08, 2015 1:54 pm

While modeling the star schema for a construction project I came across a dimension which has only 3 values (Approved , Not Approved, Approval in Progress). I was wondering is it normal to have a dimension with only 3 rows or should I put them in the fact.

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Re: Very Small Dimension Table

Post  ngalemmo on Wed Apr 08, 2015 2:23 pm

You don't want to put descriptive columns into a fact table. It burns up a lot of space and slows queries. You may want to consider combining this attribute with similar status information in a junk dimension, reducing the number of dimension tables.
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Re: Very Small Dimension Table

Post  KKumar on Wed Apr 08, 2015 6:54 pm

I thought of having a junk dimension but I don't have any other attribute other than the approval indicator. So the junk dimension will have only 2 attribute - a surrogate key and approval indicator. Is that ok?

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Re: Very Small Dimension Table

Post  ngalemmo on Wed Apr 08, 2015 7:04 pm

It's ok, and a 'pure' solution.  But, for practical purposes, if you are taking about a single character field and have no need for other information (no description or other attributes) then making it a degenerate dimension on the fact is the way to go.  Given there are a fixed and small number of possible values that are well understood, there is no need for the DW to house additional information.  That can easily be handled by supplementing the BI layer with enumerated descriptions and other information.

For example you can simply put such information (descriptions, etc...) in a table whose PK is the code. It would not be a "dimension" but rather a lookup table the BI layer can use to provide more information.
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