【判断题】【消耗次数：1】
关系代数中，自然连接操作要求两个关系的连接属性不仅具有相同的域，还需具有相同的属性名。
①
正确
②
错误
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相关题目
【单选题】
设两个关系中分别包含有m和n个属性，他们具有同一个公共属性，当对它们进行等值连接时，运算结果的关系中包含的属性个数为（ ）。
①
m*n
②
m+n-1
③
m+n
④
m+n+1
随机题目
【单选题】
Now Mike isn’t here. He ________ Mr. Green’s. Perhaps he ________ back in a few minutes.
①
went to ; is coming
②
has gone to ; will come
③
has been to ; will be
④
is going to ; has come
【单选题】
This bright girl __________ the truth in front of the enemy.
①
didn’t say
②
couldn’t speak to
③
said
④
didn’t tell
【单选题】
Every time I _________ there, I will buy him something nice.
①
went
②
will go
③
go
④
have gone
【单选题】
The bridge which ________ last year looks really beautiful.
①
was built
②
built
③
was set up
④
had been built
【单选题】
She ________ the door before she goes away.
①
had locked
②
is locking
③
has locked
④
was locking