View and nested table expression access

A nested table expression is the specification of a subquery in the FROM clause of an SQL SELECT statement. The processing of table expressions is similar that for a view.

You can determine the methods that are used by executing EXPLAIN for the statement that contains the view or nested table expression. In addition, you can use EXPLAIN to determine when set operators are used and how Db2 might eliminate unnecessary subselect operations to improve the performance of a query.

Materialization for views and nested table expressions

Materialization means that the data rows that are selected by the view or nested table expression are put into a work file that is to be processed like a table. When the column TNAME names a view or nested table expression and column TABLE_TYPE contains a W, it indicates that the view or nested table expression is materialized.