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Calculations using Physical Tables vs Logical Tables

User_HHQJ3Nov 20 2008 — edited Sep 15 2009
It's easy to find an example of where you would want to use Logical Tables instead of Physical Tables to create fact columns in the repository. Any measure such as Profit Margin (i.e. Profit / Sales) must be computed in the Logical Tables, so that the division operation occurs after the dimensional aggregations are passed to it from the physical layer. In the example of (Profit / Sales), using Physical Columns returns an incorrect result, because it does the division operation first, then aggregates all of those results into a nonsense value.

So, is there some type of formula in which the reverse is true, such that using Logical Tables would return an incorrect result, while the Physical Tables would return the correct result?

If not, then under what circumstances would we want to use the Physical Tables instead of the Logical Tables? Is there some type of formula that performs better with Physical Tables?