Wednesday, August 1, 2007

materialized view

I think there are only 2 important types of views -- traditional view ^ materialized view

materialized view = a db-server-side cache. Compare with mysql query cache [[ mysql stored procedures ]]

Compared to a standard view, A materialized view takes a different approach in which the query result is cached as a concrete (rather than virtual) table that is infrequently (rather than on-each-query) updated from the original base tables. This enables much more efficient access, at the cost of some data being potentially out-of-date. Whenever the underlying tables of a materialized view are updated, Oracle marks the materialized view as stale.

When a SQL query is issued, the query rewrite facility within Oracle will determine whether a suitable materialized view is available. If it is, Oracle will transparently rewrite the query to use the materialized view instead. This results in significantly improved performance since the query accesses the small set of rows in the materialized view rather than all the rows in the tables referenced by the query.

materialized view is most frequently used in data warehouse applications. Data warehousing applications also do not typically require access to real-time data.

MySQL does not provide Materialised Views by itself. But it is easy to build Materialised Views yourself.

MS SQL server has something similiar to materialized view -- "indexed view"

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