问题 单项选择题

SQL中可使用的通配符有______。

A.*(星号).

B.%(百分号)

C._(下划线)

D.B和C

答案

参考答案:D

解析:[知识点] 关系数据库标准语言SQL/SQL的数据查询功能 [评析] SQL中的表达式中可用的通配符有%(百分号)和(下划线),而在SELECT子句中虽然可用*(星号)来表示从表中取出所有列,但它不是通配符。 %匹配包含零个或多个字符的任意字符串。这个通配符既可以用作前缀又可以用作后缀。 匹配任意单个字符,可以作前缀也可作后缀。

填空题
阅读理解

An Australian company, Smart Car Technologies, has developed a system that lets drivers know when they’re speeding.When the technology becomes commercially available, it could help lead-footed drivers avoid tickets and also save lives.The company that developed the product hopes to convince Australian government agencies to put the technology into use in their automobile fleets.

The product, called Speed Alert, links real-time location data and speed obtained with the help of GPS(全球定位系统) to a database of posted speed limits stored in a driver’s PDA or programmable mobile phone.The setup of the product does not need to be hooked(钩住) up to a car’s speedometer.In fact, it is entirely portable.It will also work with newer phones and PDAs that have built-in GPS receivers.If a driver exceeds(超过) the speed limit, the speed is shown and an alert sounds.

Michael Paine, an Australian vehicle design engineer and traffic safety consultant, was hired to analyze the product.He told Live Science  that his colleagues in the road safety field are “very enthusiastic” about what they’re now calling “intelligent speed alert.” Other research, according to Paine, shows that 40 percent of all traffic deaths involve speeding.There is also a potentially future use: “Since the system is so portable, it would be easy to make it a requirement for teenage drivers to always use a speed alert device when driving,” Paine said.“The system even has the function to record speeding violations(违背), so parents can monitor their teenage drivers.”

The product will soon go on sale in Sydney.

41.What’s the purpose of the new product_______.

A.To inform us of the new car system.     B.To introduce some improvement in cars.

C.To limit certain drivers to safe driving.   D.To popularize the built-in car system.

42.Lead-footed drivers refer to the ones        .

A.who drive too carelessly   B.that drive extremely fast

C.who are partly disabled     D.that drive too slowly

43.The second paragraph mainly talks about        .

A.the project of the built-in product     B.why the system becomes popular

C.the functions of GPS in cars       D.how the product is programmed

44.Which of the following is true of Speed Alert according to Michael Paine?

A.Most of the traffic deaths can be avoided. 

B.Speeding violations can be easily found out.

C.The system will excite some teenage drivers.

D.The product will not be available for adults.