Listing more than one column after the by keyword affects the query by breaking a group into subgroups and applying the specified row aggregate to each level of grouping. For example, this query finds the sum of the prices of psychology books from each publisher:
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)
