【edited】 Constraints on database -


i have following table called students. if want put constraint -- each state, there no more 2 students can come same state, how express such constraint in relational algebra?

   name   |  hometown      |  gender  -----------------------------------    bob    |  nyc           |  male    alice  |  washington d.c|  female    linda  |  london        |  female    peter  |  miami         |  male    amy    |  philadelphia  |  female    lucy   |  nyc           |  female    james  |  albany        |  male    jason  |  los angeles   |  male    cindy  |  salt lake city|  female    jackson|  princeton     |  male    judy   |  seattle       |  female    marcia |  san francisco |  female    steve  |  nyc           |  male    john   |  miami         |  male

you're going need relation providing state each town. join table (on town) , give state. group result state , count occurrences, constraining count less or equal two. haven't provided required relation or relation names, can't give algebra, should find helps homework done.


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