Nest Groups with group by

Nest groups by including more than one column in the group by clause. 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, 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 groups within groups. The maximum number of group by columns (or expressions) is not explicitly limited.