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Slowing Changing Dimension (SCD) demystified – Part 2

May 4, 2012

In Part 1 of this series, we looked at SCD Type I. We would now look at the SCD Type II.  Let’s assume the table below holds historical info of call plans of a customer in the Telecom industry.

Historical information storage (As a row)

From the table above it is easy to note that customer with ID = 5 had a previous call plan/service with an ID of 3  and he’s currently on a new call plan with an ID of 5.
Even though there has been a change in the call plan/service subscribed by the customer, these changes are still kept thus making it easy to track historical changes.  Thus in SCD Type II, the old values are kept and a new row is created for each change.
Type II is the most elegant way of storing historical information of dimension attributes because it is possible to store many old records without altering the underlying table structure.

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