HP 3000 Manuals

ALLBASE/SQL Release F.0 Application Programming Bulletin for MPE/iX

Defining and Dropping View Constraints 

In contrast to table constraints, unique and referential constraints
cannot be defined on a view.  A type of check constraint is available
with the CREATE VIEW statement.  The WITH CHECK OPTION ensures that
modifications made through an updatable view satisfy all conditions of
the view definition. 

The following example defines a view check constraint named DateCheck
based on the view definition of the updatable view named RecDB.EventView:

             CREATE VIEW RecDB.EventView
                         (Event,
                          Date)
                      AS
                  SELECT RecDB.Event,
                         RecDB.Date
                    FROM RecDB.Events
                    WHERE Date >= CURRENT_DATE 
        WITH CHECK OPTION CONSTRAINT DateCheck 

When modifications are made through a view defined WITH CHECK OPTION, the
new values must be visible in the view definition.  That is, any attempt
to change data through such a view must satisfy all conditions in the
query specification.  If this is not so, the view check is violated, an
error is returned, and the statement has no effect.

Note that view check constraints are not deferrable, and a SET CHECK
DEFERRED statement does not affect them. 

Also note that to drop a view check constraint, you must drop the view
and recreate it. 

MPE/iX 5.0 Documentation