SCD type and its types

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SCD, or Slowly Changing Dimensions, is a common data warehousing technique used to manage changes in dimension data over time. A dimension is a table that contains descriptive data about an object, such as a customer or a product. The data in dimensions often changes over time, for example, a customer may change their address or a product’s description may be updated.

There are three types of SCD, each with its own approach to handling changes in dimension data:

  1. Type 1 (Overwrite): In this type of SCD, the latest data overwrites the existing data. This is the simplest approach to handling changes in dimension data, but it also discards any historical data.
  2. Type 2 (Add new version): In this type of SCD, a new version of the record is added when the data changes, instead of overwriting the existing data. This allows for the preservation of historical data, but it also results in multiple versions of the same record in the dimension table, which can make querying more complex.
  3. Type 3 (Add a new record): In this type of SCD, a new record is added when the data changes, instead of overwriting the existing data or adding a new version. This approach allows for the preservation of historical data, but it also results in multiple records for the same object in the dimension table, which can also make querying more complex.

The choice of which type of SCD to implement depends on the specific requirements of the data and the use case. For example, if historical data is not important and query performance is a priority, then Type 1 SCD may be the best option. If historical data is important and query performance is not a concern, then Type 2 or Type 3 SCD may be the better choice.