Views are customized presentations of data in one or more tables or other views. You
can think of them as stored queries. Views do not actually contain data, but instead
derive their data from the tables upon which they are based. These tables are referred
to as the base tables of the view.
Similar to tables, views can be queried, updated, inserted into, and deleted from, with
some restrictions. All operations performed on a view actually affect the base tables of
the view. Views can provide an additional level of security by restricting access to a
predetermined set of rows and columns of a table. They can also hide data complexity
and store complex queries.
Many important views are in the SYS schema. There are two types: static data dictionary
views and dynamic performance views. Complete descriptions of the views in the SYS
schema are in Oracle Database Reference.
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