4 ms·

A subset of a Cartesian product is not a Cartesian product. inb4, spare me the wisecrack “It's the Cartesian product of itself and no other factors”.

• timjver 9y ago
  > It’s a really compact syntax that deals with Cartesian product of lists. Couldn't taking the subset of a Cartesian product be considered to be dealing with one?
  • falcor84 9y ago
    Exactly. Indeed, from what I recall from relational database theory, joins are usually treated as cartesian products (outer joins) which are then filtered by the join condition.
    • catnaroek 9y ago
      An outer join a Cartesian product is not. Even if you stick to ordinary (inner) joins, they are pullbacks, not products. https://en.wikipedia.org/wiki/Pullback https://en.wikipedia.org/wiki/Pullback
      • falcor84 9y ago
        D'oh, sorry, I meant "cross join"