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我有三个表（没有创建数据库）。它们本质上相同，但数据略有不同，它们有 Company_Id 和 Category_Id。我还想将类别名称链接到此表，因此我必须加入类别。在加入之前，这有效

Select Distinct CompanyId, Category_ID From Product1 where Product1.CompanyId = 10
union
Select Distinct Distinct CompanyId, Category_ID From Product2 where Product2.CompanyId = 10
union
Select Distinct Distinct CompanyId, Category_ID From Product3 where Product3.CompanyId = 10

这让我得到了一个基于产品 ID 的产品和类别的不同列表。

我现在需要将类别名称添加到类别表中。我试过了：

    Select Distinct CompanyId, Category_ID From Product1 where Product1.CompanyId = 10
inner join Category on Category.Id=Product1.Category_ID
    union
    Select Distinct Distinct CompanyId, Category_ID From Product2 where Product2.CompanyId = 10
inner join Category on Category.Id=Product2.Category_ID
    union
    Select Distinct Distinct CompanyId, Category_ID From Product3 where Product3.CompanyId = 10
inner join Category on Category.Id=Product3.Category_ID

但返回的多部分标识符“Company.CATEGORY_ID”无法绑定。

有什么方法可以仅显示所有 3 个表中具有类别名称的不同项目？

（所以如果 product1 和 product2 都有一个 Company_ID = 10 的产品，并且有两个类别，它只会显示两次）

4

3 回答 3

2

在子句where之后。from关键字是 of的join一部分from，所以它需要放在前面where：

Select CompanyId, Category_ID
From Product1 inner join
     Category
     on Category.Id = Product1.Category_ID
where Product1.CompanyId = 10
union
Select CompanyId, Category_ID From Product2 
From Product2 inner join
     Category
     on Category.Id = Product1.Category_ID
where Product2.CompanyId = 10
union
Select CompanyId, Category_ID From Product3
From Product3 inner join
     Category
     on Category.Id = Product3.Category_ID
where Product1.CompanyId = 10;

此外，distinct distinct可能会返回错误。您不需要distinct关键字，因为您使用的是union而不是union all.

于 2013-09-06T21:00:22.757 回答
1 
    Select distinct CompanyId, Category_ID From Product1
inner join Category on Category.Id=Product1.Category_ID where Product1.CompanyId = 10
    union
    Select distinct CompanyId, Category_ID From Product2
inner join Category on Category.Id=Product2.Category_ID  where Product2.CompanyId = 10
    union
    Select distinct CompanyId, Category_ID From Product3
inner join Category on Category.Id=Product3.Category_ID where Product3.CompanyId = 10

这没有经过测试，但如果没有错字，它应该可以解决您的问题。

于 2013-09-06T21:22:34.857 回答
0

尝试这个。union我认为首先和之后执行该连接Category表会更具可读性和可维护性：

with cte as (
    select distinct CompanyId, Category_ID from Product1 where Product1.CompanyId = 10
    union 
    select distinct CompanyId, Category_ID from Product2 where Product2.CompanyId = 10
    union
    select distinct CompanyId, Category_ID from Product3 where Product3.CompanyId = 10
)
select
   P.CompanyId, P.Category_ID, c.Category_Name
from cte as P
   inner join Category as c on c.Id = P.Category_ID

或者，如果您不喜欢公用表表达式，请使用子查询：

select
   P.CompanyId, P.Category_ID, c.Category_Name
from (
    select distinct CompanyId, Category_ID from Product1 where Product1.CompanyId = 10
    union 
    select distinct CompanyId, Category_ID from Product2 where Product2.CompanyId = 10
    union
    select distinct CompanyId, Category_ID from Product3 where Product3.CompanyId = 10
)as P
   inner join Category as c on c.Id = P.Category_ID
于 2013-09-06T21:05:56.223 回答