关于SQL查询的问题

时间:2011-04-03 19:35:41

标签: sql oracle

我正在开发一个涉及oracle数据库的小项目, 我有以下表格:

CUSTOMER ( Cid, CName, City, Discount )
PRODUCT ( Pid, PName, City, Quantity, Price )
ORDERS ( OrderNo, Month, Cid, Aid, Pid, OrderedQuantity, Cost )

如何检索订购所有产品的所有客户的名称?

例如,如果客户x订购了product1,product2和product3(这是公司提供的所有产品),他将被选中。如果客户y只订购了产品1和2而不是3,则不会选择它。

我怎样才能做到这一点?

2 个答案:

答案 0 :(得分:5)

你想要“关系师”。

select *
  from customer c
 where not exists( -- There are no product
          select 'x'
            from product p
           where not exists(  -- the customer did not buy
                    select 'x'
                      from orders o
                     where o.cid = c.cid 
                       and o.pid = p.id));

select c.cid
      ,c.name
  from customer c
  join orders   o using(cid)
 group
    by c.id
      ,c.name
having count(distinct o.pid) = (select count(*) from product);

以下是Joe Celko撰写的一篇精彩文章,其中介绍了实现关系划分(和变体)的几种方法:Divided We Stand: The SQL of Relational Division

答案 1 :(得分:2)

您可以使用group by并使用having子句要求客户订购了所有产品:

select  c.CName
from    Customers c
join    Orders o
on      o.Cid = c.Cid
group by
        c.Cid
,       c.CName
having  count(distinct o.Pid) = (select count(*) from products)

恕我直言,比“关系分割”方法更具可读性,但效率较低。