connect_by_root equivalente in postgres

Dovresti usare un'espressione di tabella comune ricorsiva che semplicemente "porta" la radice attraverso i livelli di ricorsione:

with recursive fg_tree as (
  select fg_id, 
         fg_id as fg_clasifier_id -- <<< this is the "root" 
  from fg
  where parent_fg_id is null -- <<< this is the "start with" part
  union all
  select c.fg_id, 
         p.fg_clasifier_id
  from fg c 
    join fg_tree p on p.fg_id = c.parent_fg_id -- <<< this is the "connect by" part
) 
select *
from fg_tree;

Maggiori dettagli sulle espressioni di tabelle comuni ricorsive nel manuale:http://www.postgresql.org/docs/current/static/queries-with.html">http://www.postgresql.org/docs/current/static/queries-with.html www.postgresql.org/docs/current/static/queries-with.html