In a query, listing more than one column after the by keyword breaks a group into subgroups, and applies the specified row aggregate to each level of grouping.
select type, pub_id, price from titles where type = "psychology" order by type, pub_id, price compute sum(price) by type, pub_id
type pub_id price ----------- ------- ------------- psychology 0736 7.00 psychology 0736 7.99 psychology 0736 10.95 psychology 0736 19.99 Compute Result: --------------- 45.93 type pub_id price ----------- ------- ------------- psychology 0877 21.59 Compute Result: --------------- 21.59 (7 rows affected)