VIEWS

Views

A view can be understood as a logical or virtual table which does not exist physically in the database. Views are also called Dictionary Objects. Advantages of Views can be listed as below:

• Security- The confidential columns can be suppressed from viewing and manipulation.
• Complexity can be avoided.
• Logical columns can be created.
• Views can represent a subset of the data which is contained in a table.
• Views can join and simplify multiple tables into a single virtual table.
• Views can behave as aggregated tables where the database engine aggregates data such as sum, average etc. and presents the results calculated as part of the data.
• Views take very little space to store. The database contains only the definition of a view not a copy of all the data it contains.

Views can be classified into two categories based on the way they are created and they are:

• Simple View: If the view is created from a single table, it is called as the simple view. DML operations can be performed if it is Simple View.
• Complex View: If the view is created on multiple tables, it is called as a complex view.

In order to create view, we must write the following syntax:

Create View <View Name> as <Query>

For example:

• A view of instructions without their salary
  Create view faculty as
  select ID, name, dept_name
  from instructor
• Create a view of department salary totals
  create view department_total_salary(dept_name, total_salary)as
  select dept_name,sum(salary)
  from instructor
  group by dept_name;

References:

1. H.F.Korth and A. Silberschatz,"Database system concepts",McGraw Hill,2010
2. A.K.Majumdar and p, Bhattacharya,"Database Management Systems",Tata McGraw Hill,India,2004
3. F.Korth, Henry. Database System Concepts. 6th edition.