Slowly Changing Dimensions Explained: How Data Warehouses Keep History Accurate
Slowly Changing Dimensions (SCD) are techniques used in data warehousing to manage changes in dimension data over time while preserving historical accuracy. They help ensure that analytics and reports reflect the correct context of past events, even when descriptive data like customer location or product category changes. Different SCD types offer various strategies for handling these changes, from overwriting values to maintaining full historical records.
- ▪Slowly Changing Dimensions help maintain accurate historical data in data warehouses when descriptive attributes change over time.
- ▪Common SCD types include Type 0 (retain original value), Type 1 (overwrite with new value), Type 2 (track full history with new records), and Type 3 (store limited history with previous and current values).
- ▪An example use case is preserving a customer's original city at the time of sale, even if they later move to a different city.
- ▪Overwriting dimension data without using SCD methods can lead to inaccurate business reporting, such as misattributing past sales to a new customer location.
- ▪SCD Type 0 is often used for immutable fields like original signup date or first acquisition channel, which should never be updated.
- ▪SCD Type 2 is the most common method when full historical tracking is required, allowing fact tables to reference the correct dimension version at a given time.
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