【2019年8月】OCP 071認證考試最新版本的考試原題-第25題

Choose three.

Which three statements are true about defining relations between tables in a relatonal database?

A) Foreign key columns allow null values.

B) Unique key columns allow null values

C) Primary key columns allow null values.

D) Every primary or unique key value must refer to a matching foreign key value.

E) Every foreign key value must refer to a matching primary or unique key value.

Answer：ABE

(解析：AB Answer：比較簡單明瞭;D Answer：說反了)