This is particularly useful to implement trees with materialized paths [1]. Since you can filter / order by those array fields, you can implement very efficient

This is particularly useful to implement trees with materialized paths [1]. Since you can filter / order by those array fields, you can implement very efficient trees that do anything in one query, with all the benefits of relational algebra / DBMS. No need to resort to document stores to implement trees. [1] http://justcramer.com/2012/04/08/using-arrays-as-materialized-paths-in-postgres/ http://justcramer.com/2012/04/08/using-arrays-as-materialize...