NULL Values in Fact Table

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NULL Values in Fact Table

Post  jimbo1580 on Thu Jan 14, 2010 6:53 pm

In an Accumulating Snapshot that has multiple dates, where we are revisiting the fact rows as additional events occur, should the foreign keys to the date dimension for dates that have not yet occurred be set to NULL or should they point to a "dummy" row in the date dimension.

Thanks

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Re: NULL Values in Fact Table

Post  amarpal on Thu Jan 14, 2010 8:04 pm

Reference to an inferred (dummy) row in the Dim table is always preferred. Following are some of the reasons:
1. The where clause in the queries on the fact table doesn't need to consider null different from other values ("IS NULL" vs. "= Value").
2. The absence of a late arriving dimension value may be for multiple reasons and you can have one inferred (dummy) row in the Dim table for each of these reasons. These reasons will be visible in your reports based on what attribute values you store for the inferred row.

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