如何加入选择顶部

Question

我对多个表的组合有疑问。 我的SQL查询：

SELECT *
FROM CRM.Bank as a
JOIN CRM.Documents as b ON a.Bank_ID = b.Documents_ID
JOIN CRM.Counterparties as c ON c.Counterparties_ID = b.Documents_ID
JOIN CRM.Items as d ON d.Document_tran_ID = b.Documents_ID 

我有表CRM.Items，该表具有以下列：

Item_ID     Document_tran_ID    Name
=======     ================    ====
1           1                   Advertising banner
2           1                   Shipping costs
3           2                   Garden tent
4           2                   Additional fasteners
5           2                   Shipping costs

现在我有一个问题，如何仅将第一个项目连接到文档（d.Document_tran_ID = b.Documents_ID）？ 我知道我应该使用SELECT TOP。但是，我在创建正确的查询时遇到了问题

以以下形式期待结果

Bank_ID     Documents_ID        Counterparties_ID       Document_tran_ID    Name
=======     ============        =================       ================    ====
22          1                   4                       1                   Advertising banner
23          2                   20                      2                   Garden tent
24          3                   21                      3                   Other

仅匹配文档中的第一个项目。

Answer 1

我认为您可以尝试使用 CROSS APPLY 联接。在内部查询中，您可以应用订单条件以选择 TOP 行

SELECT *
FROM CRM.Bank as a
JOIN CRM.Documents as b ON a.Bank_ID = b.Documents_ID
JOIN CRM.Counterparties as c ON c.Counterparties_ID = b.Documents_ID
CROSS APPLY
  (select top 1 * from CRM.Items i where  i.Document_tran_ID = b.Documents_ID) as d

Answer 2

对文档表使用子查询

SELECT *
FROM CRM.Bank as a
JOIN ( select min(Document_tran_ID) as Documents_ID from CRM.Documents) as b ON a.Bank_ID = b.Documents_ID
JOIN CRM.Counterparties as c ON c.Counterparties_ID = b.Documents_ID
JOIN CRM.Items as d ON d.Document_tran_ID = b.Documents_ID