18、（8-7） choose two
Which two statements are true regarding views? (Choose two.)
A) A simple view in which column aliases have been used cannot be updated.
B) The OR REPLACE option is used to change the definition of an existing view without dropping
and re-creating it.
C) The WITH CHECK OPTION constraint can be used in a view definition to restrict the columns
displayed through the view.
D) Rows added through a view are deleted from the table automatically when the view is dropped.
E) Rows cannot be deleted through a view if the view definition contains the DISTINCT keyword.
F) A subquery used in a complex view definition cannot contain group functions or joins.
Answer：BE
（解析：
只要是简单视图，使用别名的列是可以使用 UPDATE 命令更新的。
WITH CHECK OPTION 用于限制通过视图更改基表的条件，禁止更改不包含在子查询条件里的行。）
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