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关系模式和元组的集合通称为( )。
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对关系S和关系R进行集合运算结果中既包含关系s中的所有元组也包含关系R中的所有元组这样的集合运算称为
并运算
交运算
差运算
除运算
对关系S和关系R进行集合运算结果中既包含关系S中的所有元组也包含关系R中的所有元组这样的集合运算称为
并运算
交运算
差运算
除运算
下列叙述中哪些是正确的 I．一个关系对应一个二维表二维表名就是关系名 II．二维表中的列称为属性属
仅I、II和III
仅I、IV和V
仅II、III、IV
都正确
设关系R和S的元数分别为r和s那么由属于R但不属于S的元组组成的集合运算称为__1__在一个关系中找
元组
属性
关键码
关系模式
关系数据模型中关系是指
元组中的一个属性值
多个属性的总称
关系模式和元组的集合
元素之间的联系的集合
设关系R和S的元数分别为r和s那么由属于R但不属于S的元组组成的集合运算称为1在一个关系中找出所有满
元组
属性
关键码
关系模式
在关系数据库中元组的集合称为关系通常标识元组的属性或最小属性组称为______
主键
定义
属性
模式
在关系数据模型中通常可以把1称为属性而把2称为关系模式常用的关系运算是关系代数和3在关系代数中对一个
集合代数
逻辑演算
关系演算
集合演算
在关系数据模型中通常可以把45称为属性而把46称为关系模式常用的关系运算是关系代数和47在关系
集合代数
逻辑演算
关系演算
集合演算
下列叙述中哪些是正确的 Ⅰ．一个关系对应一个二维表二维表名就是关系名 Ⅱ．二维表中的列称为属性属性
仅Ⅰ、Ⅱ和Ⅲ
仅Ⅰ、Ⅳ和Ⅴ
仅Ⅱ、Ⅲ、Ⅳ
都正确
在关系数据中元组的集合称为关系通常标识元组的属性或最小属性组称为______
在关系数据库中元组的集合称为关系通常标识元组的属性或最小属性组称为______
对关系S和关系R进行集合运算结果中既包含关系S中的所有元组也包含关系R中的所有元组这样的集合运算称为
并运算
交运算
差运算
除运算
下列叙述中哪些是正确的Ⅰ．一个关系对应一个二维表二维表名就是关系名Ⅱ．二维表中的列称为属性属性的个数
仅Ⅰ、Ⅱ和Ⅲ
仅Ⅰ、Ⅳ和Ⅴ
仅Ⅱ、Ⅲ、Ⅳ和Ⅴ
都正确
在关系数据模型中通常可以把__1__称为属性而把__2__称为关系模式常用的关系运算是关系代数和__
集合代数
逻辑演算
关系演算
集合演算
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