What are Views in Databases ?

A view is a virtual or logical table composed of the result set of a query. Unlike ordinary tables (base tables) in a relational database, a view is not part of the physical schema: it is a dynamic, virtual table computed or collated from data in the database. Changing the data in a table alters the data shown in the view.
Views can provide advantages over tables;
* They can subset the data contained in a table
* They can join and simplify multiple tables into a single virtual view
* Views can act as aggregated tables, where aggregated data (sum, average etc.) are calculated and presented as part of the data
* Views can hide the complexity of data, for example a view could appear as Sales2000 or Sales2001, transparently partitioning the actual underlying table
* Views do not incur any extra storage overhead
* Depending on the SQL engine used, views can provide extra security.
Just like functions (in programming) provide abstraction, views can be used to create abstraction. Also, just like functions, views can be nested, thus one view can aggregate data from other views.