What is view? why do we have view?

Views can represent a subset of the data contained in a table
Views can join and simplify multiple tables into a single virtual table
Views can act as aggregated tables, where the database engine aggregates data (sum, average etc) and presents the calculated results 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 take very little space to store; the database contains only the definition of a view, not a copy of all the data it presents
Depending on the SQL engine used, views can provide extra security
Views can limit the degree of exposure of a table or tables to the outer world