What is materialized view?

What is materialized view ?

Materialized views store both definitions of view plus rows resulting from the execution of the view. It is more efficient to use materialized views if query involves summaries, large or multiple joins or both. It is a pre-computed table comprising aggregated or joined data from fact and possibly dimensions tables. Also known as a summary or aggregate table and mainly used for improving query performance or providing replicated data.
Key Features:

1. Can define independent table space, storage parameters to Materialized views. 
2. Use Index & Partition 
3. Use query re-write feature – Process of modifying a query to use the view rather than the base table is called query rewrite. 

Types of materialized views 

1. Materialized view with Aggregates – The valid aggregate functions are: SUM, COUNT(x), COUNT(*), AVG, VARIANCE, STDDEV, MIN, and MAX 
2. Materialized views containing only joins 
3. Nested Materialized views – materialized view whose definition is based on another materialized view