Sql 从发生重复键匹配的联接中排除结果

我处理的数据来自多个我无法控制的来源。这些源的“键”值往往重复。我需要在联接中保持这些重复值中的任何一个形式匹配

使用以下数据

T1
| ID | FirstKey | SecondKey | ThirdKey | AdditionalColumns   |
+----+----------+-----------+----------+---------------------+
| 01 | Prod1    | ABC1      | 201      | Jun 2010, A, 101    |
| 02 | Prod2    | DEF2      | 202      | May 2009, A, 101    |
| 03 | Prod2    | DEF2      | 202      | May 2010, S, 101    |
| 04 | Prod3    |           | 206      | Jun 2010, A, 103    |
| 05 | Prod4    |           | 207      | Jun 2011, S, 103    |


T2
| ID | FirstKey | SecondKey | ThirdKey | AdditionalColumns   |
+----+----------+-----------+----------+---------------------+
| 01 | Prod1    | ABC1      | 201      | Jun 2010, A, 101    |
| 02 | Prod2    | DEF2      |          | May 2009, A, 101    |
| 03 | Prod2    | DEF2      | 202      | May 2010, S, 101    |
| 04 | Prod3    |           |          | Jun 2010, A, 103    |
| 05 | Prod4    |           | 207      | Jun 2011, S, 103    |
| 06 | Prod1    | ABC1      | 201      | Jun 2010, T, 101    |

现在，如果我们进行查询：

SELECT 
       T1.FirstKey, T1.SecondKey, T1.ThirdKey,
       T2.FirstKey, T2.SecondKey, T2.ThirdKey,
       T1.AdditionalColumns, T2.AdditionalColumns
FROM 
       T1 JOIN T2 ON T1.FirstKey = T2.FirstKey 
          AND T1.SecondKey = T2.SecondKey
          AND T1.SecondKey IS NOT NULL
UNION
SELECT 
       T1.FirstKey, T1.SecondKey, T1.ThirdKey,
       T2.FirstKey, T2.SecondKey, T2.ThirdKey, 
       T1.AdditionalColumns, T2.AdditionalColumns
FROM 
       T1 JOIN T2 ON T1.FirstKey = T2.FirstKey 
          AND T1.ThirdKey = T2.ThirdKey
          AND T1.SecondKey IS NULL

我们得到以下结果

FirstKey  SecondKey  ThirdKey  FirstKey  SecondKey  ThirdKey  AdditionalColumns  AdditionalColumns
--------  ---------  --------  --------  ---------  --------  -----------------  -----------------
Prod1     ABC1       201       Prod1     ABC1       201       Jun 2010, A, 101   Jun 2010, A, 101
Prod1     ABC1       201       Prod1     ABC1       201       Jun 2010, A, 101   Jun 2010, T, 101
Prod2     DEF2       202       Prod2     DEF2       202       May 2009, A, 101   May 2010, S, 101
Prod2     DEF2       202       Prod2     DEF2       202       May 2010, S, 101   May 2010, S, 101
Prod4     NULL       207       Prod4     NULL       207       Jun 2011, S, 103   Jun 2011, A, 103

我需要查询只返回具有权威匹配的记录。e、 g.两个表之间只有1个匹配项

FirstKey  SecondKey  ThirdKey  FirstKey  SecondKey  ThirdKey  AdditionalColumns  AdditionalColumns
--------  ---------  --------  --------  ---------  --------  -----------------  -----------------
Prod4     NULL       207       Prod4     NULL       207       Jun 2011, S, 103   Jun 2011, A, 103

在连接中有没有这样做的方法

目前，我可以通过为每个表生成CTE来获得唯一性，从而保证联接中使用的键的唯一性。这是可行的，但很难看，并为查询添加了大量工作

是否有其他方法来执行此联接，以排除重复的匹配项？这假设我不能基于AdditionalColumns数据以编程方式排除任何重复的行

---

我一次又一次地遇到这个问题，所以CTE方法看起来很困难，因为它一定是一个已经解决的问题。

在查询中使用GROUP BY如何：

SELECT T1.FirstKey, T1.SecondKey, T1.ThirdKey, T2.FirstKey, T2.SecondKey, T2.ThirdKey, T1.AdditionalColumns, T2.AdditionalColumns, COUNT(*)
FROM (
SELECT 
       T1.FirstKey, T1.SecondKey, T1.ThirdKey,
       T2.FirstKey, T2.SecondKey, T2.ThirdKey,
       T1.AdditionalColumns, T2.AdditionalColumns
FROM 
       T1 JOIN T2 ON T1.FirstKey = T2.FirstKey 
          AND T1.SecondKey = T2.SecondKey
          AND T1.SecondKey IS NOT NULL
UNION
SELECT 
       T1.FirstKey, T1.SecondKey, T1.ThirdKey,
       T2.FirstKey, T2.SecondKey, T2.ThirdKey, 
       T1.AdditionalColumns, T2.AdditionalColumns
FROM 
       T1 JOIN T2 ON T1.FirstKey = T2.FirstKey 
          AND T1.ThirdKey = T2.ThirdKey
          AND T1.SecondKey IS NULL
)
GROUP BY T1.FirstKey, T1.SecondKey, T1.ThirdKey, T2.FirstKey, T2.SecondKey, T2.ThirdKey, T1.AdditionalColumns, T2.AdditionalColumns
HAVING COUNT(*) = 1;

一个建议

让您的整个系统选择一个子查询。让我们把它命名为SUBQ

然后你这样做：

SELECT *
FROM (SUBQ)
GROUP BY `ThirdKey`
HAVING COUNT(*) = 1