there is currently no way to perform queries across different buckets.
So, you should just manually repeat the same query on all buckets
you're interested in, and then group the results by yourself; or, you
could arrange your data in a single bucket, using composite keys to
differentiate (i.e., department-empolyee_code where "department" would
be your "bucket"), and then perform your queries on both keys and
values.
Regards,
Sergio B.
--
Sergio Bossa
http://www.linkedin.com/in/sergiob