Listing more than one column after the keyword BY breaks a group into subgroups and applies the specified row aggregate function at each level of grouping. For example, the following 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 28.00
psychology 0736 31.96
psychology 0736 43.80
psychology 0736 79.96
sum
==========================
183.72
type pub_id price
------------ ------ --------------------------
psychology 0877 21.59
sum
==========================
21.59
(7 row(s) affected)