In SQL, a view is a virtual table based on the result-set of an SQL statement. It is a pre-established query command that is kept in the data dictionary). Unlike ordinary base tables in a relational database, a view does not form part of the physical schema: as a result set, it is a virtual table computed or collated dynamically from data in the database when access to that view is requested). Changes applied to the data in a relevant underlying table are reflected in the data shown in subsequent invocations of the view).

Views can provide several advantages over tables):

• Views can represent a subset of the data contained in a table. Consequently, a view can limit the degree of exposure of the underlying tables to the outer world: a given user may have permission to query the view, while denied access to the rest of the base 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 that it presents.
• Structures data in a way that classes of users find natural and intuitive.

To create a view, we use the CREATE VIEW statement followed by the SELECT statement that defines the view. The view always shows up-to-date data, and the database engine recreates the view every time a user queries it. Views can be updated with the CREATE OR REPLACE VIEW statement.