Is there a way to give a subquery in Oracle 11g an alias like:
select *
from
(select client_ref_id, request from some_table where message_type = 1) abc,
I don't have an Oracle instance to test with, but what you posted should be valid ANSI-89 JOIN syntax. Here it is in ANSI-92:
SELECT *
FROM (SELECT client_ref_id, request
FROM SOME_TABLE
WHERE message_type = 1) abc
JOIN (SELECT client_ref_id, request
FROM SOME_TABLE
WHERE message_type = 1) defg ON defg.client_ref_id = abc.client_ref_id