Oracle-1Z0-051－６１

QUESTION NO: 61

You created an ORDERS table with the following description:

Exhibit:

You inserted some rows in the table. After some time, you want to alter the table by creating the

PRIMARY KEY constraint on the ORD_ID column.

Which statement is true in this scenario?

A. You cannot add a primary key constraint if data exists in the column

B. You can add the primary key constraint even if data exists, provided that there are no duplicate

values(即使数据存在，如果没有重复值，你能添加主键约束）

C. The primary key constraint can be created only a the time of table creation

D. You cannot have two constraints on one column

Answer: B

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