Set visualizer with support for operations on them?

Question

SQL

Hello. Has anyone ever come across a subject from a question? The point is. I want to explain to a friend how SQL works, but it is hard to understand the visual representation of tables. Is there something like a visualizator that will have some kind of fixed data set (not the essence of what), which, using set-theoretic operations, will visually display something like Venn diagrams?
Type {A} INTERSECT {B} will show 2 sets and color the intersection area.