select
　t1.cateid, catename, t1.bookname, t1.price
from books t1
join category c on c.cateid=t1.cateid
where 3 >= (
　select count(*)
　from books t2
　where
　　t1.cateid = t2.cateid and
　　t1.price <= t2.price
)
order by cateid, price desc;