MySQL查詢->在子表中查找具有兩個條件的記錄

Question

我有兩個簡單的數據庫：

顧客：

+----+--------------------------+
| id |           customer       |
+----+--------------------------+
|  1 | Dent, Arthur             |
|  2 | Prefect, Ford            |
|  3 | Beeblebrox, Zaphod       |
+----+--------------------------+

購買：

+-------------+--------------------------+
| Customer ID |  SKU       |  Date       |
+-------------+--------------------------+
|     1       | PRODUCT1   | 2016-01-16  |
|     1       | PRODUCT3   | 2016-01-18  |
|     2       | PRODUCT2   | 2015-12-12  |
|     2       | PRODUCT1   | 2016-02-10  |
|     3       | PRODUCT3   | 2016-03-01  |
+-------------+------------+-------------+

我想做的是構造一個查詢，該查詢返回已購買PRODUCT1和PRODUCT3的所有客戶（因此在上面的示例中，應該只是Arthur Dent）。

我可以輕松地選擇一種產品； 例如

SELECT `Customer ID` FROM `Customers` a LEFT JOIN `Purchases` b 
ON a.`Customer ID` = b.`Customer ID` WHERE `SKU`=`PRODUCT1'

...但是我不知道如何僅在“客戶”中選擇“采購”中有匹配兩個SKU的相應記錄的記錄？

Answer 1

有兩種不同的方法可以做到這一點。 一種是使用聚合，另一種是多次join到purchases表：

select c.customer
from customer c
   join purchases p1 on c.id = p1.customerid and p1.sku = 'PRODUCT1'
   join purchases p2 on c.id = p2.customerid and p2.sku = 'PRODUCT3'

根據您的資料，您可能需要使用distinct這種消除重復。

---

這是聚合的替代方法：

select c.customer
from customer c
where exists (
   select 1
   from purchases p
   where sku in ('PRODUCT1','PRODUCT2')
       and c.id = p.customerid
   having count(distinct sku) = 2
)

Answer 2

您可以通過幾個exists子句來做到這一點，例如：

select c.id, c.customer
from customer 
where exists (
 select customer_id from purchases 
 where customer_id = c.id and sku = 'PRODUCT1'
)
and exists(
 select customer_id from purchases 
 where customer_id = c.id and sku = 'PRODUCT3'
);