Views

A view provides a mechanism to hide certain data from the view of certain users. Any relation that is not in the conceptual model but is made visible to a user as a “virtual relation” is called a view.

A view is defined using the create view statement which has the form:

create view v as <query expression>

where <query expression> is any legal SQL expression. The view name is represented by v.

Example: A view of instructors without their salary:

create view faculty as
select ID, name, dept_name
from instructor

Once a view is defined, the view name can be used to refer to the virtual relation that the view generates.

Note that updates made to a view will reflect in the relation from which the view was created. Since the view may not have all attributes of the relation, the remaining attributes will be given null values.

In the above example, if a new record is inserted into the view faculty, a new record will be inserted into instructor as well, but salary will be null.