ocp考试051题库解析：第29题
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ocp考试051题库解析：第29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
答案解析：
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。
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