Explain the concept of materialized views in PostgreSQL and their usage.

A materialized view in PostgreSQL is a database object that stores the result of a query as a physical table. Unlike a regular view, which is computed each time it is accessed, a materialized view stores data and allows for quick retrieval of results without re-computation.

Usage:

• Accelerating complex and resource-intensive queries, especially when data does not change frequently.
• Caching aggregated or joined data.

Features:

• Data in a materialized view is not automatically updated when the underlying tables change.
• To update the data, the REFRESH MATERIALIZED VIEW command must be executed.

Example of creation:

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

Updating data:

REFRESH MATERIALIZED VIEW sales_summary;