Explain slowly changing dimensions types 1, 2, and 3.

Slowly Changing Dimensions (SCD) manage attributes that evolve over time in a data warehouse. Type 1 overwrites the existing record with the new value, keeping only the latest state; it is simple but loses history. Type 2 adds a new row with a surrogate key and timestamps, preserving full history; it requires handling surrogate keys and effective dates. Type 3 stores the previous value in an additional column, keeping limited history; it is useful when only the last change matters. Choosing the type depends on business needs: use Type 1 for non‑critical attributes, Type 2 for audit trails and trend analysis, and Type 3 for attributes where only the immediate past is relevant. Implementing SCDs involves defining key columns, effective dates, and handling insert/update logic in ETL processes.