Type III
This method tracks changes using separate columns and preserves limited history. The Type II preserves unlimited history as it's limited to the number of columns designated for storing historical data. The original table structure in Type I and Type II is the same but Type III adds additional columns. In the following example, an additional column has been added to the to record the supplier's original state - only the previous history is stored.
| Supplier_Key | Supplier_Code | Supplier_Name | Original_Supplier_State | Effective_Date | Current_Supplier_State |
|---|---|---|---|---|---|
| 123 | ABC | Acme Supply Co | CA | 22-Dec-2004 | IL |
This record contains a column for the original state and current state—cannot track the changes if the supplier relocates a second time.
One variation of this is to create the field Previous_Supplier_State instead of Original_Supplier_State which would track only the most recent historical change.
Read more about this topic: Slowly Changing Dimension
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