G. Features Introduced in Ingres 9.1 (Ingres 2006 Release 2) : New Features in the DBMS Server : Derived Tables
 
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Derived Tables
A derived table results when you code a SELECT in the FROM clause of a SELECT or UPDATE statement.
Derived tables let you create or simplify complex queries. Useful in data warehousing applications, they provide a way to isolate complex portions of query syntax from the rest of a query.
Some complex queries cannot be implemented without using either pre-defined views or derived tables. The derived table behaves like an inline view, but is more concise and avoids having to define persistent objects that may be used for a single query only.
For details on derived tables, see the SQL Reference Guide.