在关系代数中,从两个关系的笛卡尔积中选取它们的属性或属性组间满足一定条件的元组的操作

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问题:

在关系代数中,从两个关系的笛卡尔积中选取它们的属性或属性组间满足一定条件的元组的操作称为______连接。

考点:计算机等级考试数据库技术三级数据库技术笔试92
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显微镜和望远镜中都有两组透镜,每组透镜的作用都相当于一个______,靠近眼睛的透镜叫做______.

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直放站主要由以下()设备组成。

A.施主天线

B.重发天线

C.馈缆系统

D.直放主机

E.功放

F.电源以及防雷避雷系统

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国家《节水型社会建设“十一五”规划》提出工业节水的主要任务?

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A 61-year-old woman was saved on Saturday evening by Russian rescuers after being buried for up to 127 hours in rubble in the quake-ravaged southwest China's Sichuan Province.

Local residents told Russian rescuers that there was someone alive under two collapsed residential buildings in Dujiangyan, a city southeast of the epicenter of Monday's earthquake.

The rescuers explored the buildings with dogs and machines. Then, they cut out a section of the floor, and successfully pulled out the woman.

The woman was in good condition and was still able to think clearly. She was still able to move her hands and feet and could still speak.

The Parsurvivor had lived on the first floor of the six-story building. And she was buried in the debris of the concrete ceiling after the quake.

The unidentified woman was the first survivor found by foreign rescue teams. A total of 237 rescuers from Japan, Russia, South Korea and Singapore are currently in Sichuan, aiding the disaster relief efforts.

The Russian rescuers are still trying to save a second possible survivor trapped in the debris of the building.

Into the sixth day since the devastating earthquake, China's worst in more than 30 years, rescuers, including more than 130,000 troops, were still struggling to pull possible survivors from debris of collapsed houses, schools and factories.

61. The passage mentions the following EXCEPT_______.

A. how old the survivor is

B. where the survivor lived

C. how long the survivor was trapped

D. what the survivor’s name is

62. The underlined word “debris” in Paragraph 5 can be replaced by _______.

A. ruins             B. centre                    C. middle    D. surrounding

63. The best title for the passage should be _______.

A. Russian rescue team save a woman in Dujiangyan

B. Russian rescuers find a survivor in China's quake

C. Woman saved by Russian rescuers 127 hours after quake

D. Miracle rescues save buried people in Dujiangyan

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细分市场是指具有()的一群人。每个公司都无法充分地满足市场的所有需求,因此,应选择对本公司最有吸引力的一个或多个细分市场作为营销目标,所选定的细分市场就是本公司的()。

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