【简答题】【消耗次数：1】
设有关系R（A,B,C）和关系S（C,D,E），则R与S自然连接的结果中包含的属性列个数为[填空1]列。
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相关题目
【单选题】
设有关系R(A,B,C)、S(B,C,D)，那么与R?S等价的关系代数表达式是( )。
①
π1，2，3，4（σ2=1∧3=2（R×S））
②
π1，2，3，6（σ2=1∧3=2（R×S））
③
π1，2，3，6（σ2=4∧3=5（R×S））
④
π1，2，3，4（σ2=4∧3=5（R×S））
【多选题】
设有关系模式R(A，B，C，D)，其数据依赖集：F＝{(A，B)→C，C→D}，则关系模式R不满足（ ）。
①
A.1NF
②
B.2NF
③
C.3NF
④
D.BCNF
【单选题】
若关系R和S分别有r和s个属性，分别含有m和n个元组，则R×S（ ）
①
A.包含r+s个属性和m+n个元组
②
B.包含r+s个属性和m×n个元组
③
C.包含r×s个属性和m+n个元组
④
D.包含r×s个属性和m×n个元组
【单选题】
若关系R和S分别有r和s个属性，分别含有m和n个元组，则R×S（ ）
①
包含r+s个属性和m+n个元组
②
包含r+s个属性和m×n个元组
③
包含r×s个属性和m+n个元组
④
包含r×s个属性和m×n个元组
随机题目
【单选题】
In June 1941 Hitler suddenly launched an attack ______ Russia.
①
for
②
to
③
on
④
against
【单选题】
When I awoke on the morning of Sunday, the news was brought ______ me ______Hitler’s invasion of Russia.
①
for…of
②
to…on
③
to… of
④
for… on
【单选题】
Hitler was wrong and we should ______ to help Russia.
①
go out all@go all out
②
make out all
③
make all out
【单选题】
This is no time to moralize ______ the follies of countries which have allowed themselves to be struck down one by one.
①
to
②
on
③
by
④
in
【单选题】
Hitler was however wrong and we should ______ to help Russia.
①
make all out
②
make out all
③
go all out
④
go out all
【单选题】
In June 1941 Hitler suddenly ______ an attack on Russia.
①
launched
②
exerted
③
developed
④
created
【单选题】
He said that everyone should turn their backs _____ a craving for fame and prestige.
①
for
②
down
③
up
④
on
【单选题】
The subjugation of the western Hemisphere______ his will…
①
to
②
in
③
according to
④
against
【单选题】
We shall ______ all our friends and allies in every part of the world to take the same course and pursue it.
①
appeal to
②
appeal for
③
appeal with
④
appeal of
【单选题】
He gambled ______ being able to buy a ticket at the last minute.
①
about
②
on
③
in
④
with