OCP-1Z0-051-V9.02-31题

31. 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 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 command to create a table fails. Identify the reason for the SQL statement failure? (Choose all that

apply.)

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

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

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

D. You cannot use ORD_NO and ITEM_NO columns as a composite primary key because ORD_NO is

also the FOREIGN KEY.

Answer: AC



答案解析：

scott@TESTDB> create sequence ord_seq

2 increment by 10

3 start with 120

4 maxvalue 9999

5 nocycle;



Sequence created.



scott@TESTDB> CREATE TABLE ord_items

2 (expiry_date date CHECK (expiry_date > SYSDATE));

(expiry_date date CHECK (expiry_date > SYSDATE))

*

ERROR at line 2:

ORA-02436: date or system variable wrongly specified in CHECK constraint

A 、SYSDATE不能用在CHECK约束中，对



scott@TESTDB> CREATE TABLE ord_items

2 (qty NUMBER(3) CHECK (qty BETWEEN 100 AND 200));



Table created.

B、BETWEEN可以用在约束中，B错





scott@TESTDB> CREATE TABLE ord_items

2 (ord_no NUMBER(4)DEFAULT ord_seq.NEXTVAL NOT NULL);

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

*

ERROR at line 2:

ORA-00984: column not allowed here



C、NEXTVAL不能用作默认值，C对





sh@TESTDB> create table orders

2 (ord_no number primary key);



Table created.



sh@TESTDB> create table ord_items

2 (ord_no number not null,

3 item_no number,

4 constraint ord_fk foreign key(ord_no) references orders(ord_no),

5 constraint it_pk primary key(ord_no,item_no));



Table created.



D、外键约束和字段可以和本表组合成主键，D错。