Tree-like queries

[roberth]

rel8, a competing library, supports "tree-like queries", which seem to be a nice way of retrieving data from related tables without having to mess around with left outer joins. At least, that's what I use in beam to achieve a similar effect. Manually reconstructing the haskell values from a join is a little annoying.

https://rel8.readthedocs.io/en/latest/cookbook.html#tree-like-queries