ocp試題解析:11g-1Z0-051-v9.02-035題
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35. Which two statements are true regarding constraints? (Choose two.)
A. A table can have only one primary key and one foreign key.
B. A table can have only one primary key but multiple foreign keys.
C. Only the primary key can be defined at the column and table levels.
D. The foreign key and parent table primary key must have the same name.
E. Both primary key and foreign key constraints can be defined at both column and table levels.
Answer: BE
試題解析:
A. 一個表只能有一個主鍵和一個外鍵,不正確因為一個表只能有一個主鍵,但可以有多個外鍵
B. 一個表只能有一個主鍵,但可以有多個外鍵,正確。
C. 只有主鍵能被定義成列級或表級,不正確因為除了NOT NULL只有被定義成列級,其它的約束都可以被定義成列級或表級
D. 外鍵和父表主鍵必須名字相同,不正確因為名字可以不同,但是數據類型需一致
E. 主鍵和外鍵都可以被定義成列級或表級