ocp題庫解析：11g-1Z0-051-v9.02-029題，完整題庫請點擊這里聯(lián)系老師咨詢了解

29. Which two statements are true regarding constraints? (Choose two.)

A. A foreign key cannot contain NULL values.

B. The column with a UNIQUE constraint can store NULLS .

C. A constraint is enforced only for an INSERT operation on a table.

D. You can have more than one column in a table as part of a primary key.

Answer: BD

試題解析：

A不對因為外鍵可以包含空值

C不對因為約束可以作用在INSERT,UPDATE,DELETE操作上

B正確，唯一約束可以包含空值。

D正確，可以多個組合列組成一個表的主鍵。