[solumunus]

How would you handle unmatched outer joins?

[benzayb]

By having a default value (non-null) for each declared type of those columns.

Or, the user must define a default value in the query itself.

Yes, tedious; but, precise and forces the programmer to really prepare for the "unknown" scenario.

[masklinn]

a left outer join b yields tuples of (A, Option<B>), a full outer join b yields tuples of (Option<A>, Option<B>)