If one of the purposes of relational databases is data modeling, I've always wondered why there aren't good semantics for sum types. The real world is full of them, but databases can't express them. When I bring this up, some people respond that this is the purpose of ORMs; however, this implies that we have an arbitrary bifurcation in which some of the processing happens efficiently in SQL and anything that depends on sum types has to get hoisted up and over a network to application code. Further, it allows for different clients to behave differently, possibly having different notions of what any given sum type's variants are (which leads invariably to data corruption). I really wish databases did better here, but maybe I'm missing something.