嵌套SQL语句（简单）

Question

我正在尝试运行一个查询，该查询获取订购了产品p01和p07的客户（cid）的ID。

这是我可以使用的，但是什么也没返回：

SELECT cid
FROM customers
WHERE cid IN (SELECT cid
              FROM orders
              WHERE pid IN (SELECT pid
                            FROM products
                            WHERE pid = 'p01'
                            AND pid = 'p07'));

Answer 1

您的原始查询不会返回任何行，因为

 SELECT pid 
 FROM products
 WHERE pid = 'p01' AND pid = 'p07';

永远不会返回任何行，因为将永远不会满足WHERE pid = 'p01' AND pid = 'p07'的条件。

您应该做的是：

SELECT cid
FROM customers
WHERE cid IN (SELECT cid
              FROM orders
              WHERE pid IN (SELECT pid
                            FROM products
                            WHERE pid IN ('p01', 'p07')));

您还可以使用JOIN：

SELECT DISTINCT C.cid
FROM   customers AS C 
       INNER JOIN 
       orders AS O ON O.cid = C.cid
       INNER JOIN 
       products AS P ON P.pid = O.pid
WHERE   P.pid IN ('p01', 'p07')

如果您不想使用DISTINCT，则可以执行以下操作：

SELECT  C.cid
FROM    customers AS C 
WHERE   EXISTS  (SELECT O.cid 
              FROM   orders AS O INNER JOIN 
                     products AS P ON P.pid = O.pid
              WHERE  P.pid IN ('p01', 'p07') AND O.cid = C.cid)

根据您的评论“它返回c001，c004和c006，但是客户c004只订购了其中一种产品（p01），而没有订购两种产品（p07和p01）”，我认为您需要这样做：

SELECT  C.cid
FROM    customers AS C 
WHERE   EXISTS  (SELECT O.cid 
              FROM   orders AS O INNER JOIN 
                     products AS P ON P.pid = O.pid
              WHERE  P.pid IN ('p07') AND O.cid = C.cid) AND 
        EXISTS (SELECT O.cid 
              FROM   orders AS O INNER JOIN 
                     products AS P ON P.pid = O.pid
              WHERE  P.pid IN ('p01')  AND O.cid = C.cid ) 

Answer 2

pid永远不是'p01' 和 'p07' 'p01' 'p07' 。 使用OR ，或者使用IN ：

SELECT DISTINCT customers.cid
FROM customers
JOIN orders ON orders.cid = customers.cid
WHERE orders.pid IN ('p01', 'p07')