问题 填空题

在关系数据库中,基本的关系运算有3种,它们是选择、投影和______。

答案

参考答案:连接

解析: 本题考查的是关系运算。关系数据库中,基本的关系运算有3种: 选择:从关系中找出满足给定条件的元组的操作。 投影:从关系模式中指定若干属性组成新的关系。 连接:是关系的横向结合,连接运算将两个关系模式拼接成一个更宽的关系模式,生成的新关系中包含满足连接条件的元组。

阅读理解

阅读理解。

     I needed to get some money so, after Christmas, I took a job in the clothes department at Graham's

for the first fortnight of the January sale. I can't say that I enjoyed it, but it was an experience I'll never

forget.

     I could never understand why there were so many things in the sales; where did they all come from?

Now I know the secret! Firstly, there is the special winter stock (货物) and the stock that people buy all

the year round; some of these things are slightly reduced. Secondly, there are the summer clothes they

couldn't sell last year; these are heavily reduced to clear them. Thirdly, there are cheap clothes bought in

specially for the sales; these are put out at high prices ten days before the sale begins and then are reduced

by 60% in the sale. Clever! Lastly, they buy in"seconds? (clothes not in perfect condition) for the sale and

they are sold very cheaply.

     When I arrived half an hour before opening on the first day of the sale, there was already a queue around

three sides of the building. This made me very nervous.

      When the big moment arrived to open the doors, the security guards, looking less confident than usual,

came up to them, keys in hand. The moment they had unlocked the doors, they hid behind the doors for

protection as the noisy crowd charged in. I couldn't believe my eyes; this wasn't shopping, it was a

battlefield! One poor lady couldn't keep her feet and was knocked over by people pushing from behind.

     Clothes were flying in all directions as people searched for the sizes, colors and styles they wanted.

Quarrels broke out. Mothers were using their small children to crawl (爬行) through people's legs and get

hold of things they couldn't get near themselves.

     Within minutes I had half a dozen people pushing clothes under my nose, each wanting to be the first

served. Where had the famous English Queue gone? The whole day continued like that, but I kept my

temper (脾气)! I was taking money hand over fist and began to realize why, twice a year, Graham's were

happy to turn their expensive store into a battlefield like this.

     In the sale fever, people were spending money like water without thinking whether they needed what

they were buying. As long as it was a bargain it was OK.

     You won't believe this but as soon as I got home I crashed out for four hours. Then I had dinner and

went back to bed, fearing the sound of the alarm which would tell me to get ready for the second day of

the sale.

1. Which of the following statements is true?

A. The customers gave up the queuing for which the English are famous.

B. The customers kept their temper while looking for clothes they wanted.

C. Small children enjoyed crawling through people's legs.

D. The security guards were fearless of the crowd.

2. In the author's opinion, why were Graham's happy to make their expensive store into"Battlefield?

A. There were too many clothes and they wanted to clear them in the sales.

B. They were eager to show that they were clever at doing business.

C. They could take the chance to raise the prices of all their clothes.

D. They wanted to make more money by having sales.

3. The expression "crashed out" means _______.

A. chatted with her friends

B. slept soundly

C. broke down

D. dined out

4. What would be the best title for the passage?

A. The Best Bargain.

B. Hunting for a job.

C. Sale Fever.

D. A Pleasant Fortnight.

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