choose two
Exammine the desciption of the PRODUCT DETALS table:
NAME NULL TYPE
--------------------------------------------------
PRODUCT_ID NOT NULL NUMBER(2)
PRODUCT_NAME NOT NULL VARCHAR2(25)
PRODUCT_PRICE NUMBER(8,2)
EXPIRY_DATE DATE
Which two statements are true?
A) PRODUCT_ID can be assigned the PEIMARY KEY constraint.
B) EXPIRY_DATE cannot be used in arithmetic expressions.
C) EXPIRY_DATE contains the SYSDATE by defalt if no date is assigned to it
D) PRODUCT_PRICE can be used in an arithmetic expression even if it has no value stored in it
E) PRODUCT_PRICE contains the value zero by default if no value is assigned to it.
F) PRODUCT_NAME cannot contain dupicate values.
Answer：AD
(解析：A 答案考的是如果有非空约束还能不能再添加主键约束，答案是可以。number 型的列即使是空值也可以出现在数学表达式上，但是最后的结果会是空值。)