Question

我有两张桌子。一个由客户组成，另一个由他们购买的产品组成：

表客户

CustID, Name
  1,     Tom 
  2,     Lisa 
  3,     Fred

表产品

CustID, Item
  1,     Toaster
  1,     Breadbox
  2,     Toaster
  3,     Toaster

我想让所有购买烤面包机的顾客，除非他们还买了面包箱。

所以我尝试了以下内容：

SELECT * FROM Customer
JOIN Product
    ON Customer.CustID=Product.CustID
WHERE Product in
    (SELECT 
        Item
    FROM Product
    WHERE (Item = 'Toaster' AND Item != 'Breadbox'));

和

SELECT * FROM Customer
INNER Join Product
ON Customer.CustID=PRODUCT.CustID
WHERE Product.Item = 'Toaster'
AND Product.Item NOT IN ('Breadbox');

但两者都给出了相同的结果，其中包括已经拥有面包箱的汤姆。

如何确保只有拥有烤面包机但没有面包箱的客户才能上市？

Answer 1

SELECT * FROM Customer C
LEFT JOIN Product PT ON C.CustID = PT.CustID AND PT.Item = 'Toaster'
LEFT JOIN Product PB ON C.CustID = PB.CustID AND PB.Item = 'Breadbox'
WHERE PT.Item IS NOT NULL AND PB.Item IS NULL

Answer 2

这是我的第一篇文章，原谅任何失误。 Customer和Product表之间存在“多对一”关系。要制定要应用的逻辑限制，您需要聚合Product表或连接Product表两次。实际上，你正在寻求将多对一关系折叠成“一对一”的关系。

以下是Product表连接两次的一些示例。

SELECT DISTINCT
a.Name
FROM
Customer a
JOIN Product b ON a.CustID = b.CustID
LEFT JOIN Product c on a.CustID = c.CustID AND c.Item = 'Breadbox'
WHERE
b.Item = 'Toaster' AND
c.CustID IS NULL

或（根据索引效率略低）

SELECT DISTINCT
a.Name
FROM
Customer a
JOIN Product b ON a.CustID = b.CustID
WHERE
b.Item = 'Toaster' AND
NOT EXISTS (SELECT 1 FROM Product c where a.CustID = c.CustID AND c.Item = 'Breadbox')

并且，以下是Product表连接一次的示例 - 可能比您需要的更复杂。

SELECT
a.Name
FROM
Customer a
JOIN
(
    SELECT 
    CustID, 
    SUM(case when Item = 'Toaster' then 1 else 0 end) sum_Toaster,
    SUM(case when Item = 'Breadbox' then 1 else 0 end) sum_Breadbox
    FROM
    Product
    WHERE 
    Item in ('Toaster','Breadbox')
    GROUP BY
    CustID
    HAVING
    SUM(case when Item = 'Toaster' then 1 else 0 end) > 0 AND
    SUM(case when Item = 'Breadbox' then 1 else 0 end) = 0
) b ON a.CustID = b.CustID

Answer 3

试试这个：

SELECT c.CustID, c.Name
FROM customer AS c
JOIN product AS p ON c.CustID = p.CustID
GROUP BY c.CustID, c.Name
HAVING SUM(p.Item = 'Toaster') >= 1 AND SUM(p.Item = 'Breadbox') = 0

Answer 4

SELECT distinct * FROM Customer
 LEFT JOIN Product ON Customer.CustID=Product.CustID
WHERE Item = 'Toaster'
AND Customer.CustID NOT IN (
Select CustID FROM Product Where Item = 'Breadbox'
)

Answer 5

having
        count(case when p.Item = 'Toaster'  then 1 end) > 0
    and count(case when p.Item = 'Breadbox' then 1 end) = 0

或

where

对于第二种情况，您并不严格需要{{1}}，尽管它可能有助于在大型表上执行。

选择所有客户，除非他们有其他产品 - SQL

5 个答案: