retrieving all rows from a "tree" in one select - how ?

Hi,
 I realize that a relational database may not be ideal for storing (and 
retrieving) tree-like strucutres, but it looks like you guys are doing 
with PostgreSQL the impossible anyway.

Having table t of all nodes:

CREATE SEQUENCE nodeIDseq START 1;
CREATE TABLE t(id int PRIMARY KEY DEFAULT NEXTVAL('nodeIDseq'),parent int REFERENCES t,mydata int4);
INSERT INTO t VALUES (0,0);
I was wondering whether there is a known (and perhaps working) way to do 
things like:
-- select a tree starting with node 1234 and all its descendants:
SELECT * FROM t WHERE id=1234 OR ANCESTOR(t.parent) IS 1234;

and-- select the path from tree node 2345 to the root 
SELECT * FROM t WHERE id=2345 OR DESCENTANT(t.parent) IS 2345;

(I've seen some terse soutions at 
http://www.brasileiro.net/postgres/cookbook/view-recipes.adp?section_id=2&format=long 
but they don't seem to be complete.)

(Also I've looket at ltrees from GiST, but "ltree" seems to require that 
the ID attribute contains all ancestors.)
 Thanks,
   John

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