问题 单项选择题

在关系数据库中,索引(index)是3级模式结构中的( )。

A.概念模式

B.内模式

C.模式

D.外模式

答案

参考答案:B

解析: SQL支持数据库的3级模式结构。在SQL中,模式对应于基本表(base table),内模式对应于存储文件,外模式对应于视图(view)和部分基本表.元组对应于表中的行(row),属性对应于表中的列(column)。一个表可以带若干索引,索引也存放在存储文件中。存储文件的逻辑结构组成了关系数据库的内模式,存储文件的物理结构是任意的,对用户是透明的。

阅读理解

Last Monday we did a survey about how often the students do the housework in Shiyan High School. Here are the results.

Most students do the housework twice or three times a week. They often clean their rooms. Some students do the housework five times a week. They often clean the floor. Some students help their parents on the farm. They think their parents are too busy, so they help them.

The results for “wash clothes” are interesting. Some students wash clothes once or twice a week. They often wash clothes on Saturdays or Sundays. Some students wash clothes three or four times a week. They only wash their own clothes. But most students wash their clothes once a week. And they wash clothes on Sundays.

Liu Ying, a girl in Class 4, Grade 8, has lots of housework to do. She washes the dishes and cleans the floor every day. She often cooks, sometimes three times a day. She says, “My mother isn’t healthy. My father works in another city. So I have to do most of the housework at home.”

根据短文内容,选择正确答案(10分)

小题1:From the results we know      students do the housework five times a week.

A、all                  B、most             C、some

小题2:Some students help their parents on the farm because        .

A、they think they are old enough              

B、they think their parents are too busy

C、they don’t have too much homework

小题3:How often do most students wash their clothes?

A、Once a week.         B、Twice a week.        C、Three times a week.

小题4:From the passage we know that       .

A、Liu Ying is an unhealthy student

B、Liu Ying is good at homework

C、Liu Ying has to do much housework

小题5:Which of the following is NOT true?

A、They did the survery last Monday.

B、Most students don’t do the housework.

C、Liu Ying is a student from Class 4, Grade 8.

填空题