Can you name the types of views in PostgreSQL and explain their features?

In PostgreSQL, there are several types of views:

1. Regular View — a virtual table defined by an SQL query. When accessed, the query is executed anew, and data is not stored separately.

2. Materialized View — stores the result of a query physically in the database. It allows faster data access but requires periodic refresh (REFRESH) to update the data.

3. Updatable View — a regular view to which INSERT, UPDATE, DELETE operations can be applied if it meets certain conditions (for example, contains data from a single table without aggregate functions).

Example of creating a regular view:

CREATE VIEW active_users AS
SELECT id, name FROM users WHERE status = 'active';

Materialized view:

CREATE MATERIALIZED VIEW sales_summary AS
SELECT product_id, SUM(amount) AS total_sales FROM sales GROUP BY product_id;

Materialized views are useful for speeding up complex queries but require management of data updates.