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【简答题】
PRIMARY KEY与UNIQUE比较 在一个基本表中只能定义一个_______约束,但可定义多个_______约束; 对于指定为PRIMARY KEY的一个列或多个列的组合,其中任何一个列都不能出现_______,而对于UNIQUE所约束的唯一键,则允许为空。 不能为同一个列或一组列既定义UNIQUE约束,又定义PRIMARY KEY约束。
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举一反三
【单选题】Read the introductory paragraph and pick the best thesis statement from the choices given below. : In many countries, families may live in the same geographic region for generation after generation, p...
A.
Geographic mobility is an essential ingredient of the American dream of material success and independence.
B.
Although this mobility has been essential to the economic growth of the country, it has led to many problems.
C.
Geographic mobility has contributed to a decline in traditional family relationships and a growing sense of alienation between the young and the old.
【简答题】Before having heard from Mao, I had considered myself at worst lightly singed by the last embers of Asian alienation. Indeed, given all the incredibly hip Asian artists and fashion designers and so fo...
【简答题】The theme of this story is everybody's guess. So what is yours? Attitudes towards interracial marriages (racism)? Man-woman relationships (feminism)? The unreasonable nature of women? The arrogance of...
【单选题】阅读以下程序,则执行下面语句后 m 的值是 。 int w=1,x=2,y=3,z=4,m; m=w
A.
1
B.
2
C.
3
D.
4
【多选题】活动受限对机体的影响有（）。
A.
对消化系统的影响有营养不良和便秘
B.
对泌尿系统的影响是造成原发感染
C.
对呼吸系统的影响的是形成坠积性肺炎
D.
对皮肤的主要影响是压疮
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