I'm not sure how to do this without using a JOIN (which ODB doesn't have, of course). In "generic" SQL, you might do something like this:
Select * FROM table
INNER JOIN
(SELECT max(field) AS max_of_field, key FROM table GROUP BY key) sub
ON table.field = sub.max_of_field AND table.key = sub.key
Is there an efficient way to do this in ODB, using SELECT and/or MATCH?