oracle 的初始情况（子查询的东西）

Question

对于甲骨文， 从这些表中，

表 1 CUSTOMER : has cust_fname, cust_lname, cust_id

表 2 SALESORDER : has so_number, so_custid

表 3 ITEM : has item_qty, item_sonum

while CUST_ID = SO_CUSTID and SO_NUMBER = ITEM_SONUM (FK relationship)

我想显示带有全名的客户名称（表示 cust_fname+cust_lname），而此客户（只有一个）是订购数量最多的客户（表示必须与 item_qty 做某事）。

如何为这个任务编写代码？

谢谢

Answer 1

试试

select cust_fname, cust_lname
from
(select c.cust_fname, c.cust_lname
from customer c join salesorder so on so.so_custid = c.cust_id
join ITEM i on i.item_sonum = so.so_number
group by c.cust_fname, cust_lname
order by sum(i.item_qty) desc)
where rownum = 1

Here is a sqlfiddle demo

select cust_fname, cust_lname
from
(select c.cust_fname, c.cust_lname, rank() over (order by sum(i.item_qty) desc) rnk
from customer c join salesorder so on so.so_custid = c.cust_id
join ITEM i on i.item_sonum = so.so_number
group by c.cust_fname, cust_lname
)
where rnk = 1;