tl;dr: SQL hates you and it's your fault it hates you.

to elaborate: I'm rapidly appreciating that SQL is a "bondage and discipline" language where it is impossible for SQL to fail at any given task, it can only be failed by its users/developers.

edit: further, it occurs to me also that SQL hates you because in a sane language you'd be able to write up some generic method that says "compare every element of these collections to each other" that was reusable for all possible collections. But try defining a scalar user-defined function that takes two arbitrary resultsets as parameters. But not only can I not do that, I'm a bad person for wanting that because it violates Relational Theory.