给定关系R（A,B,C,D）和关系S（C,D,E），对其进行自然连接运算R S后的属性列为（ ）个；与σR.B>S.E（R S）等价的关系代数表达式为（ ）。
问题1选项
A.4
B.5
C.6
D.7
问题2选项
A.σ2＞7(R×S)
B.π1,2,3,4,7(σ‘2’＞‘7’Λ3=5Λ4=6(R×S))
C.σ‘2’＞‘7’(R×S)
D.π1,2,3,4,7(σ2＞7Λ3=5Λ4=6(R×S))
正确答案及解析
正确答案
解析
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