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What are slowly changing dimensions in simple terms?
Slowly changing dimensions are descriptive attributes, such as a customer's region or a product's category, that change over time. The question is whether reports should show the current value or the value at the time of each transaction, and the design depends on that choice.
Common approaches:
- Type 1: overwrite the old value, so history is lost.
- Type 2: add a new row with valid-from and valid-to dates, preserving history.
Example: if a salesperson moves region, Type 1 reassigns all past sales to the new region, while Type 2 keeps past sales in the old region.
Choose based on what the business needs to report. Type 2 is more accurate historically but more complex to build and query.
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