CP363 Lecture Notes - Lecture 17: Data Definition Language, Virtual Method Table, Database
8 Apr 2019
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Document Summary
Single table derived from other tables called the defining tables. Considered to be a virtual table that is not necessarily populated. Give table name list of attribute names, and a query to specify the contents of a view. In vi attributes retain the names from base tables in v2 attributes are assigned names. Once a view is defined sql queries can use the view relation in the from clause. Responsibility of the dbms and not the user. Complex problem of efficiently implementing a view for querying. Compute the view as and when needed. do not store permanently. Modify view query into a query on underlying base tables. Physically create a temporary view table when the view is fist queried. Keep that table on the assumption that other queries on the view will follow. Requires efficient strategy for automatically updating the view table when the base tables are updated. Dbms determines what new tuples must be inserted deleted or modified
