Materialized views improve query performance by precalculating expensive join and aggregation operations on the database prior to execution and storing the results in the database. The query optimizer automatically recognizes when an existing materialized view can and should be used to satisfy a request.

Why materialized view is faster?

the big advantage of a Materialized View is extremely fast retrieval of aggregate data, since it is precomputed and stored, at the expense of insert/update/delete. The database will keep the Materialized View in sync with the real data, no need to re-invent the wheel, let the database do it for you.

What happens when materialized view is refreshed?

REFRESH MATERIALIZED VIEW completely replaces the contents of a materialized view. To execute this command you must be the owner of the materialized view. The old contents are discarded.