Type 3: Keep Previous Value

Concepts: dmScdType3

Limited History: Just the Last Two States Type 3 adds a 'previous' column alongside the current column. customer has city and previous_city. When the customer moves, the current city becomes the previous city, and the new city becomes current. Only one prior value is preserved. History beyond the immediately-previous state is lost. Type 3 is rarely used in practice. It is useful for exactly one scenario: before-and-after comparisons. 'Show me customers who changed region this quarter.' Beyond that, it is too limited. If the customer moves a third time, Portland is lost. For full history, use Type 2.