A virtual table that does not necessarily exist in the database but is generated by the DBMS from the underlying base tables whenever it’s accessed. A view is usually defined as a query that operates on the base tables to produce another virtual table.
As well as reducing complexity by letting users see the data in the way they want to see it, views have several other benefits:
- Views provide a level of security:- Views can be set up to exclude data that some users should not see. For example, we could create a view that allows a branch manager and the Payroll Department to see all staff data, including salary details. However, we could create a second view that excludes salary details, which other staff uses.
- Views provide a mechanism:- to customize the appearance of the database. For example, the Stock Control Department may wish to call the Daily Rental Rate column for videos by the simpler name, Daily Rental.
- A view can present a consistent, unchanging picture of the structure of the database:- even if the underlying database is changed (for example, columns added or removed, relationships changed, data files split, restructured, or renamed). If columns are added or removed from a data file, and these columns are not required by the view, the view is not affected by this change. Thus, a view helps provide additional data independence to that provided by the system catalog.