How-To select on a "group" function

Hi,

I would like to retrieve a record using the following SQL-Like statement:
"select max(value) from " + className

Does anyone know how to "convert" this to OQL?

I know it would be possible to retrieve all the records, then sort them
out, and pick up the first, but I would prefer to reduce the amount of
data retrieved from the database.

I also wonder if it were possible to order the "resultset" according to
one field, e.g. of SQL-like would be:
"select xxx from " + className + " order by value".

Thenk you,
Francesco.