dashilo.... :)
nepazymejau, kad visos lentos pasiekiamos per mirror schema, taip butu 
teisingai

with query_1 as
(select ... from mirror.table_B)
select
  col_1,
  ...
  col_N,
  ...
from mirror.table_A, mirror.table_B, mirror.table_C
where ....
UNION ALL
select
  col_1,
  ...
  (select col_x from query_1 where ...) col_N
  ...
from mirror.table_A, mirror.table_B, mirror.table_C
where ...
order by ...