1. ORACLE用来判断列值是否为空的操作符是____

A ==NULL

B IS NULL

C AS NULL

D NULLIS

2 分析以下的 SQL命令

SELECT i.id_number, m.id_number

FROM inventory i, manufacturer m

WHERE i.manufacturer_id = m.id_number

ORDER BY inventory.description;

如何修改上述命令使其成功执行（）

A ORDER BY description

B ORDER BY i.description

C WHERE inventory.manufacturer_id = m.id_number

ORDER BY inventory.description

D ORDER BY inventory.description;

3. 在客户定单表(CUSTOMER)中有一列为单价（PRICE），写一个SELECT命令显示所有单价在500以上的查询语句。

A SELECT * FROM CUSTOMER WHERE PRICE>500;

B SELECT * FROM CUSTOMER WHERE PRICE BETWEEN 500 AND *;

C SELECT * FROM CUSTOMER WHERE PRICE  LIKE ‘P0%’;

D SELECT * FROM CUSTOMER WHERE PRICE>=500;

4. 分析以下SQL 命令:

SELECT price

FROM inventory

WHERE price BETWEEN 1 AND 50

AND (pri