Tell me about the different types of Slowly Changing Dimensions.

Slowly Changing Dimensions (SCD) are techniques used in data warehousing to manage changes in dimension attributes over time. The most common types are:

• Type 1: Overwrite the old value with the new one. No history is kept. Use when the change is a correction or the history is irrelevant.
• Type 2: Create a new record with a new surrogate key and set effective dates. This preserves full history. It’s the most widely used type for tracking changes.
• Type 3: Add a new column to store the previous value (e.g., "PrevCity"). Only a limited history is kept, useful when you need to compare current and previous values.
• Type 4: Store the current value in the dimension table and keep a separate history table. This keeps the dimension lean while still providing full history.
• Type 5: Combine Type 1 and Type 2 by keeping a current record and a history table, often used when you need both quick lookups and audit trails.

Choosing the right type depends on business requirements for auditability, query performance, and storage constraints.