table usagelog:

 fk_username |      fk_domain      | diskusage  |          log_date          
-------------+---------------------+------------+----------------------------
 foo         | example.org         |  398107912 | 2010-12-11 13:48:00.385656
 foo         | example.org         |  398107912 | 2010-12-12 13:48:00.385656
 foo         | example.org         |  398107912 | 2010-12-13 13:48:00.385656
 bar         | example.org         |  398107912 | 2010-12-14 13:48:00.385656
 bar         | example.org         |  398107912 | 2010-12-11 13:48:00.385656
 bar         | example.org         |  398107912 | 2010-12-12 13:48:00.385656


table box:

 username |      fk_domain      
----------+---------------------
 foo      | example.org
 bar      | example.org
 jg       | example.com