12. Managing Tables and Views : Views
 
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Views
A view can be thought of as a virtual table. Only the definition for the view is stored, not the data. A table on which a view operates is called a base table.
A view definition can encompass 1 to 380 base tables. It can involve multiple tables joined together by their common columns using a where qualification.
A view can be created on other views or on physical database tables.
Notes:
A view can be defined on any valid SELECT query that does not contain an ORDER BY, FIRST n, or FETCH FIRST clause.
Up to 128 table objects (table, view, synonym, and index) can used in a view with the default DBMS Server stack size. To allow the full count of 380 table objects the stack_size needs to be raised to 1.5m (1572864). Failure to do so may result in the session error E_OP08A2.
Primary uses for views include:
Providing security by limiting access to specific columns in selected tables, without compromising database design
Simplifying a commonly used query
Defining reports
UNION ALL views that combine tables of current, recent, and archived data
Because a view is a device designed primarily for selecting data, all selects on views are fully supported. Simply use a view name in place of a table name in the SELECT statement. Updating views is also supported on simple single table views (see Updates on Views), but updating a database by means of a view is not recommended.