True about updates through a view

Question

hi frds
i just need the right answer for the choices mentioned below with explanation
plz help me
What is true about updates through a view?
A. You cannot update a view with group functions.
B. When you update a view group functions are automatically computed.
C. When you update a view only the constraints on the underlying table will be in effect.
D. When you update a view the constraints on the views always override the constraints on the underlying tables.

Answer 1

And a very tricky only it is.
Peter, you are correct that view constraints are not enforced in the sense of PKs and FKS, but there are two other view constraints that are enforced.
SQL> CREATE TABLE t AS
  2  SELECT rownum id, object_name
  3  FROM all_objects
  4  WHERE rownum < 11;
Table created.
SQL> CREATE VIEW t_read AS
  2  SELECT * FROM t
  3  WITH READ ONLY;
View created.
SQL> CREATE VIEW t_check AS
  2  SELECT * FROM t
  3  WHERE mod(id,2) = 0
  4  WITH CHECK OPTION;
View created.
SQL> CREATE VIEW t_nocheck AS
  2  SELECT * FROM t
  3  WHERE MOD(id, 2) = 0;
View created.
SQL> INSERT INTO t_read VALUES (100, 'READ ONLY');
INSERT INTO t_read VALUES (100, 'READ ONLY')
ERROR at line 1:
ORA-01733: virtual column not allowed here
SQL> INSERT INTO t_check VALUES (100, 'EVEN ID');
1 row created.
SQL> INSERT INTO t_check VALUES (101, 'ODD ID');
INSERT INTO t_check VALUES (101, 'ODD ID')
ERROR at line 1:
ORA-01402: view WITH CHECK OPTION where-clause violation
SQL> INSERT INTO t_nocheck VALUES(100, 'EVEN ID');
1 row created.
SQL> INSERT INTO t_nocheck VALUES(101, 'ODD ID');
1 row created.
SQL> UPDATE t_check SET id = 201
  2  WHERE id = 2;
UPDATE t_check SET id = 201
ERROR at line 1:
ORA-01402: view WITH CHECK OPTION where-clause violation
SQL> UPDATE t_nocheck SET id = 201
  2  WHERE id = 2;
1 row updated.The WITH READ ONLY constraint bars all changes to the view. The WITH CHECK OPTION stops any changes that would make the record invisible to the view. It is essentially a CHECK constraint on the view.
John