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lang=EN-US>(</SPAN><SPAN
style="FONT-FAMILY: 宋体">学号，课程号，名次</SPAN><SPAN
lang=EN-US>)</SPAN><SPAN
style="FONT-FAMILY: 宋体">，若每一名学生每门课程有一定的名次，每门课程每一名次只有一名学生，则以下叙述中错误的是</SPAN><U><SPAN
lang=EN-US> (39) </SPAN></U><SPAN
style="FONT-FAMILY: 宋体">。</SPAN></P>
<P class=MsoNormal><SPAN lang=EN-US> (35)
A</SPAN><SPAN style="FONT-FAMILY: 宋体">、层次模型</SPAN><SPAN lang=EN-US>
B</SPAN><SPAN style="FONT-FAMILY: 宋体">、网状模型</SPAN><SPAN
lang=EN-US> C</SPAN><SPAN
style="FONT-FAMILY: 宋体">、关系模型</SPAN><SPAN lang=EN-US>
D</SPAN><SPAN style="FONT-FAMILY: 宋体">、三级模式结构</SPAN></P>
<P class=MsoNormal><SPAN lang=EN-US> (36)
A</SPAN><SPAN style="FONT-FAMILY: 宋体">、结构完全不一致</SPAN><SPAN
lang=EN-US> B</SPAN><SPAN
style="FONT-FAMILY: 宋体">、结构完全一致</SPAN><SPAN
lang=EN-US> C</SPAN><SPAN
style="FONT-FAMILY: 宋体">、结构部分一致</SPAN><SPAN
lang=EN-US> D</SPAN><SPAN
style="FONT-FAMILY: 宋体">、主键一致</SPAN></P>
<P class=MsoNormal><SPAN lang=EN-US> (37)
A</SPAN><SPAN style="FONT-FAMILY: 宋体">、去掉相同的属性名</SPAN><SPAN
lang=EN-US> B</SPAN><SPAN
style="FONT-FAMILY: 宋体">、去掉了重复的列</SPAN><SPAN
lang=EN-US> </SPAN></P>
<P class=MsoNormal style="TEXT-INDENT: 49.65pt"><SPAN
lang=EN-US>C</SPAN><SPAN style="FONT-FAMILY: 宋体">、行都不相同</SPAN><SPAN
lang=EN-US>
D</SPAN><SPAN style="FONT-FAMILY: 宋体">、属性值都不相同</SPAN></P>
<P class=MsoNormal style="TEXT-INDENT: 13.25pt"><SPAN
style="FONT-FAMILY: 宋体">（</SPAN><SPAN lang=EN-US>38</SPAN><SPAN
style="FONT-FAMILY: 宋体">）</SPAN><SPAN lang=EN-US> A</SPAN><SPAN
style="FONT-FAMILY: 宋体">、</SPAN><SPAN lang=EN-US><SPAN
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style="FONT-FAMILY: 宋体">（</SPAN><SPAN lang=EN-US>R</SPAN><SPAN
style="FONT-FAMILY: 宋体">）为取属性值为</SPAN><SPAN lang=EN-US>A</SPAN><SPAN
style="FONT-FAMILY: 宋体">、</SPAN><SPAN lang=EN-US>C</SPAN><SPAN
style="FONT-FAMILY: 宋体">的两列组成新关系</SPAN></P>
<P class=MsoNormal style="TEXT-INDENT: 49.65pt"><SPAN
lang=EN-US>B</SPAN><SPAN style="FONT-FAMILY: 宋体">、</SPAN><SPAN
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style="FONT-FAMILY: 宋体">（</SPAN><SPAN lang=EN-US>R</SPAN><SPAN
style="FONT-FAMILY: 宋体">）为取属性值为</SPAN><SPAN lang=EN-US>A</SPAN><SPAN
style="FONT-FAMILY: 宋体">、</SPAN><SPAN lang=EN-US>C</SPAN><SPAN
style="FONT-FAMILY: 宋体">的两列组成新关系</SPAN></P>
<P class=MsoNormal style="TEXT-INDENT: 49.65pt"><SPAN
lang=EN-US>C</SPAN><SPAN style="FONT-FAMILY: 宋体">、</SPAN><SPAN
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</xml><![endif]-->(R)</SPAN><SPAN
style="FONT-FAMILY: 宋体">与</SPAN><SPAN lang=EN-US><SPAN
style="POSITION: relative; TOP: 6pt"><!--[if gte vml 1]><v:shape
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style="FONT-FAMILY: 宋体">（</SPAN><SPAN lang=EN-US>R</SPAN><SPAN
style="FONT-FAMILY: 宋体">）是等价的</SPAN></P>
<P class=MsoNormal style="TEXT-INDENT: 49.65pt"><SPAN
lang=EN-US>D</SPAN><SPAN style="FONT-FAMILY: 宋体">、</SPAN><SPAN
lang=EN-US><SPAN style="POSITION: relative; TOP: 6pt"><!--[if gte vml 1]><v:shape
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<o:OLEObject Type="Embed" ProgID="Equation.3" ShapeID="_x0000_i1029" DrawAspect="Content" ObjectID="_1150541252">
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</xml><![endif]-->(R)</SPAN><SPAN
style="FONT-FAMILY: 宋体">与</SPAN><SPAN lang=EN-US><SPAN
style="POSITION: relative; TOP: 6pt"><!--[if gte vml 1]><v:shape
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style="FONT-FAMILY: 宋体">（</SPAN><SPAN lang=EN-US>R</SPAN><SPAN
style="FONT-FAMILY: 宋体">）是不等价的</SPAN></P>
<P class=MsoNormal><SPAN lang=EN-US> (39)
A</SPAN><SPAN style="FONT-FAMILY: 宋体">、</SPAN><SPAN
lang=EN-US>(</SPAN><SPAN style="FONT-FAMILY: 宋体">学号，课程号</SPAN><SPAN
lang=EN-US>)</SPAN><SPAN style="FONT-FAMILY: 宋体">和</SPAN><SPAN
lang=EN-US>(</SPAN><SPAN style="FONT-FAMILY: 宋体">课程号，名次</SPAN><SPAN
lang=EN-US>)</SPAN><SPAN style="FONT-FAMILY: 宋体">都可以作为候选键</SPAN></P>
<P class=MsoNormal style="TEXT-INDENT: 49.65pt"><SPAN
lang=EN-US>B</SPAN><SPAN style="FONT-FAMILY: 宋体">、只有</SPAN><SPAN
lang=EN-US>(</SPAN><SPAN style="FONT-FAMILY: 宋体">学号，课程号</SPAN><SPAN
lang=EN-US>)</SPAN><SPAN style="FONT-FAMILY: 宋体">能作为候选键</SPAN></P>
<P class=MsoNormal style="TEXT-INDENT: 49.65pt"><SPAN
lang=EN-US>C</SPAN><SPAN
style="FONT-FAMILY: 宋体">、关系模式属于第三范式</SPAN></P>
<P class=MsoNormal style="TEXT-INDENT: 49.65pt"><SPAN
lang=EN-US>D</SPAN><SPAN style="FONT-FAMILY: 宋体">、关系模式属于</SPAN><SPAN
lang=EN-US>BCNF</SPAN></P>
<P class=MsoNormal
style="MARGIN-LEFT: 18pt; TEXT-INDENT: -18pt"></FONT><SPAN
lang=EN-US style="FONT-FAMILY: 宋体"><FONT lang=ZH-CN face=宋体
size=2>●<SPAN
style="FONT-WEIGHT: normal; FONT-STYLE: normal; FONT-FAMILY: Times New Roman; FONT-VARIANT: normal">
</SPAN></FONT></SPAN><FONT lang=ZH-CN face=宋体 size=5><FONT
lang=ZH-CN face=宋体 size=2><!--[if gte vml 1]><v:shapetype
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<P class=MsoNormal
style="LAYOUT-GRID-MODE: char; LINE-HEIGHT: 12pt"><SPAN
lang=EN-US>R.C<S.B</SPAN></P></v:textbox></v:shape><![endif]--><![if !vml]><span style='mso-ignore:vglayout;position:
absolute;z-index:1;left:300px;top:31px;width:62px;height:21px'><img width=62
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<P></P></FONT><![if !mso]><![endif]><FONT lang=ZH-CN face=宋体 size=2>
<P> </P>
<P><SPAN style="FONT-FAMILY: 宋体">关系</SPAN><SPAN
lang=EN-US>R</SPAN><SPAN style="FONT-FAMILY: 宋体">和</SPAN><SPAN
lang=EN-US>S</SPAN><SPAN
style="FONT-FAMILY: 宋体">如下表所示，关系代数表达式</SPAN><SPAN lang=EN-US><SPAN
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style="FONT-FAMILY: 宋体">的结果为</SPAN><U><SPAN lang=EN-US>
(40) </SPAN></U><SPAN
style="FONT-FAMILY: 宋体">，与该表达式等价的</SPAN><SPAN
lang=EN-US>SQL</SPAN><SPAN
style="FONT-FAMILY: 宋体">语句为</SPAN><U><SPAN lang=EN-US>
</SPAN><SPAN style="FONT-FAMILY: 宋体">（</SPAN><SPAN
lang=EN-US>41</SPAN><SPAN style="FONT-FAMILY: 宋体">）</SPAN><SPAN
lang=EN-US> </SPAN></U><SPAN
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