60、(16-10) choose the best answer:

Evaluate the following sql commands:

sql>CREATE SEQUENCE ord_seq

INCREMENT BY 10

START WITH 120

MAXVALUE 9999

NOCYCLE;

sql>CREATE TABLE ord_items

(ord_no NUMBER(4) DEFAULT ord_seq.NEXTVAL NOT NULL,

item_no NUMBER(3),

qty RIUNBER(3) CHECK (qty BETWEEN 100 AND 200),

expiry_date date CHECK (expiry_date > SYSDATE),

CONSTRAINT it_pk PRIMARY REY (ord_no,item_no),

CONSTRAINT ord_fk FOREIGN KEY(ord_no) REFERENCES orders(ord_no));

The command to create a table fails. Identify the reason for the sql statement failure.

A) You cannot use SYSDATE in the condition of a CHECK constraint.

B) You cannot use the NEXTVAL sequence value as a DEFAULT value for a column.

C) You cannot use the BETWEEN clause in the condition of a CHECK constraint.

D) You cannot use ORD_NO and ITEM_NO columns as a composite primary key because ORD_NO is also the FOREIGN KEY.

Answer：A

(check 约束中明确要求不能：

参考 CURRVAL,NEXTVAL,LEVEL,和 ROWNUM 这样的伪列

调用 SYSDATE,UID,USER,和 USERENV 函数

参考其它列值的查询

)