From [the documentation][1]:

You can specify only unique, primary key, and foreign key constraints on views. However, you can define the view using the WITH CHECK OPTION clause, which is equivalent to specifying a check constraint for the view.

So it seems that there is no way to hint to the RDBMS that the underlying data (after the UNION ALL inline view is created) is NOT NULL.

This all seems a bit silly, given the UNION/UNION ALL/INTERSECT/MINUS statements all require matching datatypes! [1]: http://docs.oracle.com/cd/E11882_01/server.112/e26088/clauses002.htm#i1002565

From the documentation:

You can specify only unique, primary key, and foreign key constraints on views. However, you can define the view using the WITH CHECK OPTION clause, which is equivalent to specifying a check constraint for the view.

So it seems that there is no way to hint to the RDBMS that the underlying data (after the UNION ALL inline view is created) is NOT NULL.

This all seems a bit silly, given the UNION/UNION ALL/INTERSECT/MINUS statements all require matching datatypes!