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Suppose that I have two union- and intersection-compatible relations; i.e., R1(A,B) and R2(C,D) as:

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Now , I want to find the join of both relations with equality conditions A=C and B=D.

I have taken the cartesian product of both relations and then picked those tuples which satisfy the equality condition. So, I get the resultant relation as:

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Since it is giving the intersection of both relations and both are union- and intersection-compatible, so, can I write resultant relation as:

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According to me ,resultant relation after equi join of R1(A,B) and R2(C,D) contains four attributes and intersection of R1(A,B) and R2(C,D) contains two attributes. So, both resultant relations are different. So, we can't write equijoin of R1(A,B) and R2(C,D) = intersection of R1(A,B) and R2(C,D) here.

Am I right?

  • Please give a reference to your relational algebra--there are many. PS What is that equality equation doing in your question? PS Please use text, not images/links, for text & tables. – philipxy Nov 15 '18 at 9:09

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