Summary: An alternate approach, offered in response to our original post, provides excellent improvements for smaller databases, but clustered indexes offer better performance as database size increases. (This posting is by Dave.)
Jay Pipes suggested an alternate approach to improving MySQL performance of Query 17 on a TPC-H-like database.
select
sum(li.l_extendedprice) / 7.0 as avg_yearly
from lineitem li
inner join part p on li.l_partkey = p.p_partkey
inner join ( select
l_partkey, 0.2 * avg(l_quantity) as quantity
from lineitem
group by l_partkey