OCP-1Z0-051-题目解析-第1题

1. View the Exhibit and examine the structure of the SALES, CUSTOMERS, PRODUCTS, and TIMES tables.

The PROD_ID column is the foreign key in the SALES table, which references the PRODUCTS table.

Similarly, the CUST_ID and TIME_ID columns are also foreign keys in the SALES table referencing the CUSTOMERS and TIMES tables,

respectively.

Evaluate the following CREATE TABLE command:

CREATE TABLE new_sales(prod_id, cust_id, order_date DEFAULT SYSDATE)
AS
SELECT prod_id, cust_id, time_id
FROM sales;

Which statement is true regarding the above command?

题目翻译：查看下图并检查销售、客户、产品、日期表的结构。PROD_ID是销售表參考产品表的外键，相同的，CUST_ID和TIME_ID也是销售表的外键，分别參照了客户表和日期表，评估以下创建表的语句。CREATE……，哪一个表述是正确的？

A. The NEW_SALES table would not get created because the DEFAULT value cannot be specified in the column definition.

B. The NEW_SALES table would get created and all the NOT NULL constraints defined on the specifiedcolumns would be passed to the new table. 

C. The NEW_SALES table would not get created because the column names in the CREATE TABLE command and the SELECT clause do not match. 

D. The NEW_SALES table would get created and all the FOREIGN KEY constraints defined on the specified columns would be passed to the new table.

Answer: B

 答案解析：

A：不能创建表，原因是不能在定义字段指定默认值 （错误，我们能够再创建表的同一时候。通过Default指定相关字段的默认值）
B: 能够创建表。NOT NULL约束也能够传递到新表中 （正确，能够通过desc NEW_SALES 查看新表的结构）
C: 不能创建表，由于创建表的字段名和被选中表的字段名不一样 （错误，仅仅要是相应字段的数据类型一致就能够了，字段名能够不一样）
D：能够创建表，而且全部的外键约束也会传递到新表中 （错误，通过desc NEW_SALES能够发现仅仅有非空约束传递到了新表）