Let R(A,B,C,D,E) be a relation schema and F = {A→C, B→D, C→E, E→A}, Find all candidate keys.
I believe that there exists no CK's in this set due to not being able to map. B or D to any other relation besides B -> D . Does this mean that that there are no Candiate Keys? Although I am able to map A to all other entities besides B and D.
There are three candidate keys.
B doesn't appear on the right-hand side of any functional dependency. That means B must be part of every candidate key. I think that alone doesn't guarantee there is at least one candidate key, but it should be clear from inspection that AB is one of the three candidate keys here.
Your textbook should include at least one algorithm for determining the set of all candidate keys. If you're lucky, it includes one algorithm suitable for paper and pencil, and another suitable for automation by programming.