Database Reference
In-Depth Information
Figure 19.8
Joining Four Tables
Is Easy When Three
Are Joined in a
View.
19.5.2
Views and DML Commands
Although views have no data of their own, it is possible in certain cases to
use views to modify data in the base table that is queried by the view. This
can be very useful for tables for which the user does not have permission to
access the base table but has access to a view.
Oracle Database has rules that it tests against any view to determine
whether it is inherently updatable. An inherently updatable view is one in
which some or all of the view's columns pass the test and can be used to update
the base table. Some of the rules for simple views include the following:
The view must not be created with the WITH READ ONLY clause.
The view cannot contain GROUP BY, group functions, ORDER BY,
or DISTINCT.
The view cannot contain a subquery in the SELECT clause.
The view must include the primary key and all NOT NULL col-
umns, unless there are provisions (such as default values or a trigger)
that plug values into the NOT NULL columns.
