Database Reference
In-Depth Information
Example 15:
The following statements change methods used for materialized
view refresh.
13.4 Summary and Concluding Remarks
Let us summarize what we have covered in this chapter:
•
A logical view is a virtual relation that allows end users to
access information in a manner that is consistent with their
requirements. The view is created by the
Create-View
statement,
which simply allows few required keywords to be inserted ahead
of a query (see Figure
13-2
).
•
The view is treated just like a normal base table. It can be
designed to be updateable or read-only.
•
The
Alter-View
statement facilitates modification of the view, and
the
Drop-View
statement facilitates deletion of the view.
•
Views are very beneficial in enhancing logical data independence,
facilitation of assorted external views of the database,
simplification of the perception of end users, and enhancing
system security.
•
SQL facilitates the enforcement of a stringent security mechanism
at three levels: access to the system, access to system resources,
and access to data.
•
Access to the system is controlled by profiles and user accounts.
SQL provides statements for creating, altering and dropping of
profiles as well as user accounts.
•
Access to system resources is controlled by privileges and roles.
You can grant privileges and/or roles to users via the
Grant
statement, and revoke them via the
Revoke
statement. You can
lump privileges together by creating a role via the
Create-Role
statement, and then granting the privileges to the role. The role
can then be granted to or revoked from other users. Of course, a
role can be altered (via the
Alter-Role
statement) and dropped
(via the
Drop-Role
statement).
