A view must be enabled for optimization before its statistics
can be used to optimize a query. A view that is enabled for optimization
is known as a statistical view.
About this task
A view that is not a statistical view is said to be disabled
for optimization and is known as a regular view. A view
is disabled for optimization when it is first created. Use the ALTER
VIEW statement to enable a view for optimization. For privileges and
authorities that are required to perform this task, see the description
of the ALTER VIEW statement. For privileges and authorities that are
required to use the RUNSTATS utility against a
view, see the description of the RUNSTATS command.
A
view cannot be enabled for optimization if any one of the following
conditions is true:
- The view directly or indirectly references a materialized query
table (MQT). (An MQT or statistical view can reference a statistical
view.)
- The
view directly or indirectly references a catalog table.
- The view is inoperative.
- The view is a typed view.
- There is another view alteration request in the same ALTER VIEW
statement.
If the definition of a view that is being altered to enable
optimization contains any of the following items, a warning is returned,
and the optimizer will not exploit the view's statistics:
- Aggregation or distinct operations
- Union, except, or intersect operations
- OLAP specification