SCD Type 1, the attribute value is overwritten with the new value, obliterating the historical attribute values.For example, when the product roll-up changes for a given product, the roll-up attribute is merely updated with the current value. SCD Type 2,a new record with the new attributes is added to the dimension table. Historical fact table rows continue to reference the old dimension key with the old roll-up attribute; going forward, the fact table rows will reference the new surrogate key with the new roll-up thereby perfectly partitioning history. SCDType 3, attributes are added to the dimension table to support two simultaneous roll-ups - perhaps the current product roll-up as well as “current version minus one”, or current version and original.
SCD Type 1 the attribute value is overwritten with the new value obliterating the historical attribute values.For example when the product roll-up changes for a given product the roll-up attribute is merely updated with the current value. SCD Type 2 a new record with the new attributes is added to the dimension table. Historical fact table rows continue to reference the old dimension key with the old roll-up attribute; going forward the fact table rows will reference the new surrogate key with the new roll-up thereby perfectly partitioning history. SCDType 3 attributes are added to the dimension table to support two simultaneous roll-ups - perhaps the current product roll-up as well as current version minus one or current version and original.
Type I Type II Type III Dimensions: Type I -Changed attribute overwrites the existing one. eg: If income of customer changes from 4000 to 5000 it will simply replace 4000 by 5000. Type II Dimension - For the changed attribute a new record is created. eg: If the income of customer is changed from 4000 to 5000 then a new record is created with income 5000 and the previous one will remain as itis.This will help us to record the history of data. Type III Dimension -Here a new column will be added to capture the change. eg: If the income of customer increases from 4000 to 5000 then a new column will be added to the existing row titled new income .So in that record 2 cols will be there income and new income .
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