What’s the difference between a view and a materialized view in Snowflake?

In Snowflake, both views and materialized views are database objects that allow you to organize and present data in a structured manner, but they have different purposes and behavior:

**Views:**

1. **Definition:** A view is a virtual table defined by a SQL query. It doesn't store data itself; it provides a dynamic way to access data from one or more underlying tables.
2. **Data:** Views don't store data. They retrieve data in real-time based on the query definition when queried.
3. **Usage:** Views are suitable for simplifying queries, abstracting complex data structures, enforcing data security, and providing a logical layer over the underlying tables.
4. **Maintenance:** Views are easy to maintain as they don't store data. Changes in the underlying tables are immediately reflected in the view's data.
5. **Performance:** Views can improve query performance by encapsulating complex joins, calculations, and filtering.

**Materialized Views:**

1. **Definition:** A materialized view is a precomputed, physical copy of a result set from a SQL query. It stores data, unlike regular views.
2. **Data:** Materialized views store data that is periodically refreshed based on the query's definition. The data is computed and saved at the time of refresh.
3. **Usage:** Materialized views are suitable for improving query performance by precomputing and storing aggregates, summaries, or other complex calculations.
4. **Maintenance:** Materialized views need periodic refreshes to stay up to date. Depending on the refresh frequency, there can be a lag between changes in the underlying data and updates in the materialized view.
5. **Performance:** Materialized views can significantly improve query performance for certain types of analytical queries by reducing the need for complex calculations during runtime.

In summary, the key differences lie in how data is stored and refreshed. Views provide a dynamic view of data in real-time, whereas materialized views offer improved performance by storing precomputed data that requires periodic refreshes. The choice between using a view or a materialized view depends on your specific use case and performance optimization requirements.