En Oracle esto se hace fácilmente usando CONNECT BY
select message_id, parent_id, message_content
from messages
start with message_id = 97 -- this is the root of your conversation
connect by prior message_id = parent_id;
Esto recorre el árbol de arriba a abajo.
Si desea recorrer el árbol desde un solo mensaje hasta la raíz, cambie el start with y el connect by parte:
select message_id, parent_id, message_content
from messages
start with message_id = 100 -- this is the root of your conversation
connect by prior parent_id = message_id; -- this now goes "up" in the tree
