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