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?
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答案：默认sysdate可以在列出被指定。
sh@TEST0924> CREATE TABLE new_sales(prod_id, cust_id, order_date DEFAULT SYSDATE) AS
2 SELECT prod_id, cust_id, time_id FROM sales;
Table created.
B答案：NULL约束会传递。由以下可以看出，not null是可以传递的。B正确
第一种方法，查看表的结构，可见not null约束是可以传递的。
sh@TEST0924> desc SALES
Name Null? Type
----------------------------------------------------- -------- ------------------------------------
PROD_ID NOT NULL NUMBER
CUST_ID NOT NULL NUMBER
TIME_ID NOT NULL DATE
CHANNEL_ID NOT NULL NUMBER
PROMO_ID NOT NULL NUMBER
QUANTITY_SOLD NOT NULL NUMBER(10,2)
AMOUNT_SOLD NOT NULL NUMBER(10,2)
sh@TEST0924> desc new_sales
Name Null? Type
----------------------------------------------------- -------- ------------------------------------
PROD_ID NOT NULL NUMBER
CUST_ID NOT NULL NUMBER
ORDER_DATE NOT NULL DATE
第二种方法：由下面的查询看出，not null也是传递的。B正确
sh@TEST0924> select a.owner,a.TABLE_NAME,b.COLUMN_NAME,a.CONSTRAINT_NAME,a.CONSTRAINT_TYPE,a.SEARCH_CONDITION
2 from USER_CONSTRAINTS a,USER_CONS_COLUMNS b
3 where a.CONSTRAINT_NAME=b.CONSTRAINT_NAME and A.table_name='SALES';
OWNER TABLE_NAME COLUMN_NAME CONSTRAINT_NAME CONSTRAINT SEARCH_CONDITION
---------- ---------- --------------- ------------------------------ ---------- ------------------------------
SH SALES CUST_ID SALES_CUSTOMER_FK R
SH SALES PROD_ID SALES_PRODUCT_FK R
SH SALES TIME_ID SALES_TIME_FK R
SH SALES CHANNEL_ID SALES_CHANNEL_FK R
SH SALES PROD_ID SYS_C0011009 C "PROD_ID" IS NOT NULL
SH SALES CUST_ID SYS_C0011010 C "CUST_ID" IS NOT NULL
SH SALES TIME_ID SYS_C0011011 C "TIME_ID" IS NOT NULL
SH SALES CHANNEL_ID SYS_C0011012 C "CHANNEL_ID" IS NOT NULL
SH SALES PROMO_ID SYS_C0011013 C "PROMO_ID" IS NOT NULL
SH SALES QUANTITY_SOLD SYS_C0011014 C "QUANTITY_SOLD" IS NOT NULL
SH SALES AMOUNT_SOLD SYS_C0011015 C "AMOUNT_SOLD" IS NOT NULL
SH SALES PROMO_ID SALES_PROMO_FK R
12 rows selected.
sh@TEST0924> l
1 select a.owner,a.TABLE_NAME,b.COLUMN_NAME,a.CONSTRAINT_NAME,a.CONSTRAINT_TYPE,a.SEARCH_CONDITION
2 from USER_CONSTRAINTS a,USER_CONS_COLUMNS b
3* where a.CONSTRAINT_NAME=b.CONSTRAINT_NAME and A.table_name='NEW_SALES'
sh@TEST0924> /
OWNER TABLE_NAME COLUMN_NAME CONSTRAINT_NAME CONSTRAINT SEARCH_CONDITION
---------- ---------- --------------- ------------------------------ ---------- ------------------------------
SH NEW_SALES PROD_ID SYS_C0011428 C "PROD_ID" IS NOT NULL
SH NEW_SALES CUST_ID SYS_C0011429 C "CUST_ID" IS NOT NULL
SH NEW_SALES ORDER_DATE SYS_C0011430 C "ORDER_DATE" IS NOT NULL
C答案：
由A中所见，此表是可以创建的，虽然字段名不一样，但数据库类型一样，就可以创建表。C错误。
D答案：
由B第二种方法看出，仅仅只是传递了not null约束，而SALES_PRODUCT_FK，SALES_CUSTOMER_FK，SALES_TIME_FK这三个外键约束是没有被传递的。