Views are computed tables.
You can use views to show database users exactly the information
you want to present, in a format you can control.
Similarities between Views and Base Tables
Views are similar to the permanent tables of the database
(a permanent table is also called a base table)
in many ways:
- You can assign access permissions to views just as to base
tables.
- You can perform SELECT
queries on views.
- You can perform INSERT and
DELETE operations on some views.
- You can create views based on other views.
Differences Between Views and Permanent Tables
There are some differences between views and permanent tables:
- You cannot create indexes on views.
- INSERT, DELETE, and UPDATE operations can only be performed on certain views.
- You cannot assign integrity constraints and keys to views.
- Views refer to the information in base tables, but do not hold
copies of that information. Views are recomputed each time you invoke them.
Benefits of Tailoring Data Access
Views are used to tailor access to data in the database. Tailoring
access serves several purposes:
- By not allowing access to information that is not relevant.
- By presenting users and application developers with data in a
more easily understood form than in the base tables.
- By centralizing in the database the definition of common
queries.