Oracle to Postgres

Hello All,

I am trying to migrate from Oracle to Postgres. I have a query in
Oracle which has clauses like STARTS WITH and CONNECT BY. For
ex::

SELECT field1, field2, field3 FROM table1
START WITH table1.some1||table1.some2 IN
(
SELECT ...FROM ....WHERE ...
)
CONNECT BY PRIOR ... AND PRIOR ....
...
...

How can i implement the same functionality in Postgres???

Please guide.
thanks and regards