2. View the Exhibit to examine the description for the SALES table.
    Which views can have all DML operations performed on it? (Choose all that apply.)


A. CREATE VIEW v3
AS SELECT * FROM SALES WHERE cust_id = 2034
WITH CHECK OPTION;

B. CREATE VIEW v1
AS SELECT * FROM SALES
WHERE time_id <= SYSDATE - 2*365
WITH CHECK OPTION;
C. CREATE VIEW v2
AS SELECT prod_id, cust_id, time_id FROM SALES
WHERE time_id <= SYSDATE - 2*365
WITH CHECK OPTION;

D. CREATE VIEW v4
AS SELECT prod_id, cust_id, SUM(quantity_sold) FROM SALES WHERE time_id <= SYSDATE - 2*365
GROUP BY prod_id, cust_id
WITH CHECK OPTION;


---updateable的视图有二种,一种是继承基表的视图, 一种是使用instead of的触发器来实现

继承的视图DML操作需要满足一下条件:
1. 视图必须包含基表的每一列.
2. 视图不能包含一下操作: set, distinct, aggregate or analytic function, group by, order by, model, connect by, start with
                                   subquery in select, with read only.



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