1、select * from t_customer where cust_name like '__a%';
2、create index idx_fu_order_date on t_order(to_char(order_date,'yyyy-mm-dd'));
3、select a.cust_id,b.cust_name,a.order_sum
from (select rownum rn,cust_id,order_sum from t_order order by order_sum desc) a,
t_customer b
where a.rn <=5
and a.cust_id = b.cust_id;