SQL & PL/SQL :: Avoiding Repetition Of Condition In Not Exist Clause?

Given two tables in a 1:N relationship, I want to retrieve, for each parent row, any child row which either satisfies some condition cond1 or, if no child rows matching cond1 exist, which satisfies another condition cond2.

I can easily write such a query using NOT EXISTS, but I am forced to repeat the condition cond1. This is inconvenient, as the repeated condition is quite long (involving other tables as well), and I would like to write it only once.

For example (using the HR schema included in Oracle 10g XE): I want to retrieve, for each department, all the "new" employees (hired after a certain date) or, if no "new" employees exist, the department manager.

SELECT d.department_id,
d.department_name,
d.manager_id,
e.employee_id,
e.first_name,
e.last_name,

[code].....