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是销售表参考产品表的外键，同样的，CUST_ID和TIME_ID也是销售表的外键，分别参照了客户表和日期表，评估下面创建表的语句，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 specified

columns 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，我们可以再创建表的同时，通过Default指定相关字段的默认值）
B: 可以创建表，NOT NULL约束也可以传递到新表中 （正确，可以通过desc NEW_SALES 查看新表的结构）
C: 不能创建表，因为创建表的字段名和被选中表的字段名不一样 （错误，只要是对应字段的数据类型一致就可以了，字段名可以不一样）
D：可以创建表，并且所有的外键约束也会传递到新表中 （错误，通过desc NEW_SALES可以发现只有非空约束传递到了新表）