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OCP-1Z0-051-2015-54題

QUESTION NO: 54
Which statements are correct regarding indexes? (Choose all that apply.)
A. For each data manipulation language (DML) operation performed, the corresponding indexes
are automatically updated.
B. A nondeferrable PRIMARY KEY or UNIQUE KEY constraint in a table automatically creates a
unique index.
C. A FOREIGN KEY constraint on a column in a table automatically creates a non unique key
D. When a table is dropped, the corresponding indexes are automatically dropped
Answer: A,B,D

Explanation:

A正確,在具有索引的表上提交每項DML 操作後,都意味著必須更新相應的索引。 B正確,在表定義中定義了PRIMARY KEY 或UNIQUE 約束條件,則會自動建立一個唯一的索引。 C錯誤,外來鍵不能夠自動建立索引,只有主鍵約束和唯一性約束才能自動建立唯一的索引。
D正確,在刪除表時,會刪除相應的索引。