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In set theory, every relation is a subset of a Cartesian product. In relational algebra, relations resulting from set theory operators like Union, Intersection, etc. are new relations.

What Cartesian product are these new relations a subset of?

Even with unary operators it is not clear to me.

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    $\begingroup$ Please do not cross-post to multiple sites, you are wasting readers efforts & subverting site protocols. Please edit per feedback. $\endgroup$
    – philipxy
    Commented Nov 13 at 1:06
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    $\begingroup$ Where did you see "every relation is a subset of Cartesian product" & who said it & what do you think they meant? If you don't know what it means, why are you trying to apply it in random situations? (Rhetorical.) PS If you have a question about an operator quote the definition & format as a quote & say where you got it & who wrote it & where/why you are 1st stuck understanding. How to Ask Help center $\endgroup$
    – philipxy
    Commented Nov 13 at 1:09
  • $\begingroup$ I already told you at your 1st post "The set of rows of a relation value is a subset of (the set of rows that is) the Cartesian product of the domains of its attributes. This is independent of operators." And the book that you took the image from for your 1st post says the same thing. $\endgroup$
    – philipxy
    Commented Nov 13 at 1:11
  • $\begingroup$ "If you have a question about an operator quote the definition & format as a quote & say where you got it & who wrote it & where/why you are 1st stuck understanding." PS There are many relational algebras. They differ in operators & even what a relation is. Give operator definitions & your reference for yours. Eg textbook name, edition & page. $\endgroup$
    – philipxy
    Commented Nov 14 at 0:52

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