Let be the following simplified database sketch:
R1(P,S),R2(S,T) and R3(T,S) with P= people S = Sport and T= Sports Center
How to find in relational algebra and relational calculus which couples such that each one has at least a sport that the other do and and another that the other do not.
Πp1,p2(σs1!=s2, p1!=p2(R1))P→P1,P→P2, S→S1, S→S2
But I know this is wrong, It doesn't express the second condition at least and I'm not sure on how to express variables renaming.
Can you help me express such inclusive and exclusive relations?