Limitation of Update through views

When modifying data through a view (that is, using INSERT or UPDATE statements) certain limitations exist depending upon the type of view.

1. Views that access multiple tables can only modify one of the tables in the view.
2. Views that use functions, specify DISTINCT, or utilize the GROUP BY clause may not be updated.
3. Views having columns with derived (i.e., computed) data in the SELECT-list
4. Views that do not contain all columns defined as NOT NULL from the tables from which they were defined

ref:http://www.craigsmullins.com/cnr_0299b.htm