QUESTION 30 关于check约束

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QUESTION 30
Evaluate the following CREATE TABLE commands:
CREATE TABLE orders
(ord_no NUMBER(2) CONSTRAINT ord_pk PRIMARY KEY,
ord_date DATE,
cust_id NUMBER(4));
CREATE TABLE ord_items
(ord_no NUMBER(2),
item_no NUMBER(3),
qty NUMBER(3) CHECK (qty BETWEEN 100 AND 200),
expiry_date date CHECK (expiry_date > SYSDATE),
CONSTRAINT it_pk PRIMARY KEY (ord_no,item_no),
CONSTRAINT ord_fk FOREIGN KEY(ord_no) REFERENCES orders(ord_no));

The above command fails when executed. What could be the reason?

A. SYSDATE cannot be used with the CHECK constraint.
B. The BETWEEN clause cannot be used for the CHECK constraint.
C. The CHECK constraint cannot be placed on columns having the DATE data type.

D. ORD_NO and ITEM_NO cannot be used as a composite primary key because ORD_NO is also theFOREIGN KEY

答案：A

解析：

A选项错，sysdate不能用在check约束中，如果去掉sysdate，其他都运行成功。

SQL> CREATE TABLE orders  2  (ord_no NUMBER(2) CONSTRAINT ord_pk PRIMARY KEY,  3  ord_date DATE,  4  cust_id NUMBER(4));Table created.SQL> CREATE TABLE ord_items  2  (ord_no NUMBER(2),  3  item_no NUMBER(3),  4  qty NUMBER(3) CHECK (qty BETWEEN 100 AND 200),  5  expiry_date date CHECK (expiry_date > to_date('20140201','YYYYmmdd')),  6  CONSTRAINT it_pk PRIMARY KEY (ord_no,item_no),  7  CONSTRAINT ord_fk FOREIGN KEY(ord_no) REFERENCES orders(ord_no));Table created.SQL> CREATE TABLE ord_items1  2  (ord_no NUMBER(2),  3  item_no NUMBER(3),  4  qty NUMBER(3) CHECK (qty BETWEEN 100 AND 200),  5  expiry_date date CHECK (expiry_date >sysdate),  6  CONSTRAINT it_pk PRIMARY KEY (ord_no,item_no),  7  CONSTRAINT ord_fk FOREIGN KEY(ord_no) REFERENCES orders(ord_no));expiry_date date CHECK (expiry_date >sysdate),                                     *ERROR at line 5:ORA-02436: date or system variable wrongly specified in CHECK constraint

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