You can list more than one column in the group by clause to nest groups. Once the sets are established with group by, the aggregates are applied. This statement finds the average price and the sum of book sales, grouped first by publisher identification number and then by type:
select pub_id, type, avg(price), sum(total_sales) from titles group by pub_id, type
pub_id type ------ ------------ ------ ------- 0736 business 2.99 18,722 0736 psychology 11.48 9,564 0877 UNDECIDED NULL NULL 0877 mod_cook 11.49 24,278 0877 psychology 21.59 375 0877 trad_cook 15.96 19,566 1389 business 17.31 12,066 1389 popular_comp 21.48 12,875 (8 rows affected)
You can nest many groups within groups, up to the maximum of 16 columns or expressions specified with group by.
