Нова функция в PostgreSQL 9.2, но не тествах заявката:
Следвам урока от тук .
select row_to_json(t)
from (
select ParentTable.parentTableFirstProp, (
select array_to_json(array_agg(row_to_json(child)))
from (
select childTableFirstProp
from ChildTable
where ChildTable.id=ParentTable.parentToChildReference
) child
) as parentToChildReference
from ParentTable
) t