41.Which two statements are true regarding views? (Choose two.)

41.Which two statements are true regarding views? (Choose two.)
A.A subquery that defines a view cannot include the GROUP BY clause.
B.A view that is created with the subquery having the DISTINCT keyword can be updated.
C.A view that is created with the subquery having the pseudo column ROWNUM keyword cannot be updated.
D.A data manipulation language ( DML) operation can be performed on a view that is created with the subquery having all the NOT NULL columns of a table.
答案：CD
解析：
视图有两种
1.简单视图:包含一个子查询，只从一个基表中检索数据
2.复杂视图:包含一个子查询，从多个基表中检索数据，使用group by或distince子句对行分组，包含函数的调用,或者伪列
只能对简单视图执行dml操作
A:错误，复杂视图可以包括group by语句
B:错误，复杂视图不能执行dml语句
C:正确，包含rownum列，属于复杂视图，不能执行dml操作
D:正确，视图可以执行插入操作的前提是，该视图包含所有基表中not null的列