• A view is a logical representation of datafrom one or more tables or views
• A view contains no data itself.
• Only the query is stored in the data dictionary, i.e., the actual data is not copied anywhere.

Uses of View

• To represent a subset or superset of data.
• To restrict data access from other user. (Only by displaying selective columns)
• To present different views of the same kind  data.
• To minimize application and data source changes

Example:
CREATE VIEW emp_view AS
SELECT ename as Emp_Name, sal*12 as Annual_Sal
FROM empWHERE deptno= 20;
 We can retrieve data from a view  from any table.
  SELECT * from emp_view;

Restrictions on the view subquery

• The view subquery cannot select the CURRVAL or NEXTVAL pseudocolumns.
• If the view subquery selects the ROWID, ROWNUM, or LEVEL pseudocolumns, those columns must have aliases in the view subquery.
• If the view subquery uses an asterisk (*) to select all columns of a table, and if  later  we are adding  new columns to the table, the view will not contain those columns until we re-create the view.

Read-Only View Example
The following statement creates a read-only view named view_ empof the emptable. Only the employee’s names and salary are visible in this view:
CREATE OR REPLACE VIEW view_emp
AS SELECT ename, salFROM emp
WITH READ ONLY;

CREATE MATERIALIZED VIEW scott.emp AS
 SELECT * FROM This email address is being protected from spambots. You need JavaScript enabled to view it.;

Updatable Materialized Views
CREATE MATERIALIZED VIEW scott.emp FOR UPDATE AS
 SELECT * FROM This email address is being protected from spambots. You need JavaScript enabled to view it.;