This example is kind of tricky, bu perhaps it points one problem in the query builder. `distinct([field])` will not add that field to the select array, it will just make sure that the result does not have duplicated values for that set of columns. In the case of mysql, that is done by injecting that field list into the `GROUP BY`, whereas in postgres it uses `DISTINCT ON(country)`. Maybe have an example without the field list and then another for showing the filtering by columns.