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[单选题]
如题7图,两个关系R1和R2,运算能得到关系R3的是( )
A.连接
B.笛卡儿积
C.并
D.交
A
B
C
D
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试题答案:
A
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请用SQL语句完成如下授权:授予用户CHEN查询、修改关系S的权限,并且允许CHEN将这些权限转授给其他用户。
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在SQL Server 2000中,可以完成多个数据库之间的数据转换和转移的工具是()。
22.安全性确保用户被限制在做其想做的事情;而完整性确保用户所做的事情是________。
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在SQL查询语言中,用于合并查询的谓词是( )A.ExistsB.AllC.UnionD.Some
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1.
16.曹操的次子是
2.
11.下列关于行政征收的表述错误的是
3.
五、V. Daily Conversation ( 15 points )
4.
我国规定有五种法定社会保险项目:( )( )( )( )( )。养老保险是最为重要的险种。
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21.Many household accidents could have been prevented, but accidents seem to make news headlines every day. While accidents can happen anytime or anywhere, parents with young children can prevent accidents at home by taking a few steps. First, set your water heater correctly: To avoid burns from hot water, make sure your water heater’s temperature is set below 120° Fahrenheit, or set to “low”. Anything above that temperature can cause a child serious burns within seconds. Second, beware of candles: Statistics show that the small candle flames cause approximately 15,000 home fires a year. If you have young children and pets, stop using candles or be sure to blow them out before leaving a room. Third, recognize danger signals: It is important to pay attention to signs of danger from electrical appliances. If the wiring in your home does not function normally, you need to update it. Potential warning signs that might require an electrician’s inspection include wavering(摇晃的)TV pictures or computer screens, flickering(闪烁的)lights and shocks from appliances. It is impossible to prevent all accidents, so it is necessary to create a fire escape plan. In addition to having a smoke alarm on every floor of your home, draw a simple floor plan of your home. On it, mark two exits from every room, including windows and an outside family assembly point, such as a drive way or parking lot.(10分)21.1 The possible target readers of this passage are ______.(2分)A. grandparentsB. parentsC. grandparents with young childrenD. parents with small kids参考答案:D
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