View (SQL)

Article summary

In a database, a view is the result set of a stored query that presents a limited perspective of the database to a user. This pre-established query command 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 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 Sales2020 or Sales2021, 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.…

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