Order by lower(column-alias) doesn't work...

Hi.

This works:
select p.firstname, p.lastname, p.firstname || p.lastname as fullname from
onp_crm_person p order by fullname;

But this doesn't:
select p.firstname, p.lastname, p.firstname || p.lastname as fullname from
onp_crm_person p order by lower(fullname);
ERROR: column "fullname" does not exist
LINE 1: ... as fullname from onp_crm_person p order by lower(fullname);

This is just an example-query, in my real query I have a more complex query
generating an array of a custom-type which is then referenced to as a
column-alias, and then ORDER BY on a function tranforming this array doesn't
work:

SELECT ...
ARRAY(WITH RECURSIVE t AS (SELECT
...
) SELECT ROW(t.entity_id, t.name)::BigIntVarChar from t order by level DESC)
as folder_parent_array

ORDER BY bigintvarchar_to_text_value_flatten(folder_parent_array) ASC;
column "folder_parent_array" does not exist

What bigintvarchar_to_text_value_flatten() does is to take the "varchar"-part
out of the BigintVarchar-type and "flatten" the array by that value so that it
sorts nicely.

Any way round this?

--
Andreas Joseph Krogh