Er der en måde at give en underforespørgsel et alias i Oracle 11g SQL?

Du kan give en forespørgsel et navn eller alias med CTE's (Common Table Expressions) aka WITH-klausul aka af Oracle som Subquery Factoring:

WITH abc as (select client_ref_id, request from some_table where message_type = 1)
select * 
from abc
    inner join 
    (select client_ref_id, response  from some_table where message_type = 2) defg
       on abc.client_ref_id = def.client_ref_id;