以前没见过。。。
数据库这一块这是大啊。。。
select distinct y.cid from orders x, orders y where y.pid = x.pid and x.aid = 'a06';
1
2原来要实现的目的是：
3Get cid values of customers who order a product for which an order is also placed by agent a06.
4~~关键就是这个词了
5ps:几个表
6CUSTOMERS cid cname city discnt
7PRODUCT pid pname city quantity price
8AGENTS aid aname city percent
9ORDERS ordno month cid aid pid qty dollars