OCP题库解析：11g-1Z0-051-v9.02-029题

OCP题库解析：11g-1Z0-051-v9.02-029题，完整题库请点击这里联系老师咨询了解

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

试题解析：

A不对因为外键可以包含空值

C不对因为约束可以作用在INSERT,UPDATE,DELETE操作上

B正确，唯一约束可以包含空值。

D正确，可以多个组合列组成一个表的主键。