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.
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.
There are some differences between views and permanent tables:
You cannot create indexes on views.
You cannot perform INSERT, DELETE, and UPDATE operations on all 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.
Views are used to tailor access to data in the database. Tailoring access serves several purposes:
