What is a materialized view?

Answer

A materialized view is a database object that stores the precomputed result of a query physically on disk, unlike a regular view which runs its query every time it is accessed. This makes reads of expensive aggregations or joins very fast, at the cost of stale data and the need to refresh. Refreshes can be manual, scheduled, or in some databases incremental, updating only what changed. Materialized views are common in analytics and reporting where the same heavy query is run repeatedly and slight staleness is acceptable.