sql - 同一张表上的多个Join-Oracle

Question

我尝试了以下查询

SELECT Customer.*,
       ElectrnicItem.Product1 AS ElectronicItem1,
       ElectrnicItem.Product2 AS ElectronicItem2,
       ElectrnicItem.Product3 AS ElectronicItem3,
       ApparelItem.Product1 AS ApparelItem1,
       ApparelItem.Product2 AS ApparelItem2,
       ApparelItem.Product3 AS ApparelItem3
FROM Customer
LEFT JOIN Inventory AS ElectrnicItem 
ON (Customer.CustomerID = ElectrnicItem.CustomerID)
LEFT JOIN Inventory AS ApparelItem 
ON (Customer.CustomerID = ApparelItem.CustomerID)

但它总是返回：

ORA-00918 列定义不明确

Answer 1

我创建了表 Customer 和 Inventory，还插入了您提供的值。以下是查询：

select customer.*,ElectrnicItem.Product1 as ElectronicItem1,
ElectrnicItem.Product2  as ElectronicItem2,
ElectrnicItem.Product3 as ElectronicItem3,
ApparelItem.Product1 as ApparelItem1,
ApparelItem.Product2 as ApparelItem2,
ApparelItem.Product3 as ApparelItem3 
from customer 
left join inventory as ElectrnicItem on 
(customer.CustomerID = ElectrnicItem.CustomerID ) 
left join inventory as ApparelItem 
on (customer.CustomerID = ApparelItem.CustomerID )

它工作正常并给出以下结果：

    1   David Miller    mobile  headphone   trimmer mobile  headphone   trimmer
    2   Johnson         jeans   tshirt      NULL   jeans    tshirt      NULL               
    3   Diggs           NULL    NULL        NULL    NULL    NULL        NULL            

您提到的预期输出将永远无法实现。因为Customer表包含CustomerIdand CustomerName，所以Customer.*将同时检索CustomerIdand CustomerName。所以CustomerName列不能包含任何NULL 值。

Answer 2

这个怎么样？

SELECT a.customer_id, a.customer_name, b.product1 electronicitem1,
       b.product2 electronicitem2, b.product3 electronicitem3,
       c.product1 apparelitem1, c.product2 apparelitem2,
       c.product3 apparelitem3
 FROM customer a, inventory b, inventory c
WHERE a.customer_id = b.customer_id(+)
  AND b.product_type(+) = 'Electronic'
  AND a.customer_id = c.customer_id(+)
  AND c.product_type(+) = 'Apparel';

Answer 3

您缺少任何用于将库存中的行标识为“电子”或“服装”的谓词。不确定这是解决方法。

Answer 4

好的，有点晚了，但是...您不使用 AS 为 Oracle 中的表起别名，而只是为列起别名。尝试从表别名中删除所有这些 AS：

SELECT Customer.*,
       ElectrnicItem.Product1 AS ElectronicItem1,
       ElectrnicItem.Product2 AS ElectronicItem2,
       ElectrnicItem.Product3 AS ElectronicItem3,
       ApparelItem.Product1 AS ApparelItem1,
       ApparelItem.Product2 AS ApparelItem2,
       ApparelItem.Product3 AS ApparelItem3
FROM Customer
LEFT JOIN Inventory ElectrnicItem 
ON (Customer.CustomerID = ElectrnicItem.CustomerID)
LEFT JOIN Inventory ApparelItem 
ON (Customer.CustomerID = ApparelItem.CustomerID)