Has someone ready created an aggregate function that reduces a set of
numbers to a reduced form.  I'm writing some middleware software that needs
to know the IDs of some tuples but the query could return tens or thousands
of tuples.  I'm thinking if there were an aggregate function that would
reduce the network traffic.

select reduced_to_ranges(id)
from some_large_table
where some_field = some_value

 ID
----
1
2
3
4
5
11
12
45

Reduced form: 1-5,11-12,45