Difference between Views & Materialized views

Materialized views are disk based and update periodically base upon the query
definition.

Views are virtual only and run the query definition each time they are accessed.

Views evaluate the data in the tables underlying the view definition at the time the view
is queried. It is a logical view of your tables, with no data stored anywhere else. The
upside of a view is that it will always return the latest data to you. The downside of
a view is that its performance depends on how good a select statement the view is
based on. If the select statement used by the view joins many tables, or uses joins
based on non-indexed columns, the view could perform poorly.

Materialized views are similar to regular views, in that they are a logical view of your
data (based on a select statement), however, the underlying query resultset has been
saved to a table. The upside of this is that when you query a materialized view, you are
querying a table, which may also be indexed. In addition, because all the joins have
been resolved at materialized view refresh time, you pay the price of the join once (or
as often as you refresh your materialized view), rather than each time you select from
the materialized view. In addition, with query rewrite enabled, Oracle can optimize a
query that selects from the source of your materialized view in such a way that it
instead reads from your materialized view. In situations where you create materialized
views as forms of aggregate tables, or as copies of frequently executed queries, this
can greatly speed up the response time of your end user application. The downside
though is that the data you get back from the materialized view is only as up to date as
the last time the materialized view has been refreshed.

Materialized views can be set to refresh manually, on a set schedule, or based on
the database detecting a change in data from one of the underlying tables. Materialized
views can be incrementally updated by combining them with materialized view logs,
which act as change data capture sources on the underlying tables.


Materialized views are most often used in data warehousing / business intelligence
applications where querying large fact tables with thousands of millions of rows would
result in query response times that resulted in an unusable application.


Some other excellent stuff on difference between Views & Materialized views:
SQL Snippets: http://www.sqlsnippets.com/en/topic-12874.html
Code Project: http://www.codeproject.com/Articles/16346/Materialized-Views-in-Oracle