Question

我有许多记录代表相同的信息，但与其他表的键不同。我需要按照它们的公共属性（Att1，Att2，Att3）对这些记录进行分组，然后选择所有公共记录的单个RecordID作为这些公共记录的masterID。仅当masterID为null时，才需要将masterID添加到它所代表的每个记录中。我无法更改数据结构，所有表值都是GUID。我试过MAX，但是我没有得到分组。

TableA (Current State)

RecordID          Att1         Att2     Att3     MasterID
1                 A            B        C        
2                 A            B        C
3                 A            B        C
4                 D            E        F
5                 D            E        F
6                 D            E        F
7                 G            H        I         7
8                 G            H        I         7
9                 G            H        I         7

更新：添加了预期结果。

TableA (Expected Result)

RecordID          Att1         Att2     Att3     MasterID
1                 A            B        C        1
2                 A            B        C        1
3                 A            B        C        1
4                 D            E        F        4
5                 D            E        F        4
6                 D            E        F        4
7                 G            H        I        7
8                 G            H        I        7
9                 G            H        I        7

Answer 1

哎呀，我不喜欢这个设置。你违反了良好的规范化实践，并且存在一些需要“外部”知识的固有假设。但是，你已经说过你不能改变它......

我相信以下内容应该有效（供应商中立）：

UPDATE TableA as a SET masterId = (SELECT MIN(b.recordId) 
                                   FROM TableA as b
                                   WHERE b.att1 = a.att1
                                   AND b.att2 = a.att2
                                   AND b.att3 = a.att3)
WHERE masterId IS NULL

<小时/> 编辑：

一旦发现可以订购GUID，但无法传递MIN()或MAX()（什么？） -

你有（至少）三个选择：

将guid转换为可传递类型（即 - SELECT MIN(CAST(b.recordId as CHAR(36)))）。但是，这很可能表现不佳，仅仅是因为它会抛出每一行（参见，这就是为什么内部ID最好是简单的整数）。

尝试此供应商中立声明：

UPDATE TableA as a SET masterId = (SELECT b.recordId
                                   FROM TableA as b
                                   LEFT JOIN TableA as c
                                   ON c.att1 = b.att1
                                   AND c.att2 = b.att2
                                   AND c.att3 = b.att3
                                   AND c.recordId < b.recordId
                                   WHERE b.att1 = a.att1
                                   AND b.att2 = a.att2
                                   AND b.att3 = a.att3
                                   AND b.recordId <= a.recordId
                                   AND c.recordId IS NULL)
WHERE masterId IS NULL

SQL Server还有这个更惯用的版本：

UPDATE Updating
SET Updating.masterId = Origin.recordId
FROM TableA Updating
JOIN (TableA Origin
      LEFT JOIN TableA Exclusion
             ON Exclusion.att1 = Origin.att1
                AND Exclusion.att2 = Origin.att2
                AND Exclusion.att3 = Origin.att3
                AND Exclusion.recordId < Origin.recordId) 
  ON Exclusion.recordId IS NULL
     AND Origin.att1 = Updating.att1
     AND Origin.att2 = Updating.att2
     AND Origin.att3 = Updating.att3
WHERE Updating.masterId IS NULL

SQL Fiddle example

Answer 2

试试这个：

UPDATE m
SET
    MasterID = s.RecordID
FROM TableA AS m
INNER JOIN (
    SELECT Att1, Att2, Att3, MIN(RecordID) AS RecordID          
    FROM TableA 
    GROUP BY Att1, Att2, Att3
) AS s
    ON m.Att1 = s.Att1 AND m.Att2 = s.Att2 AND m.Att3 = s.Att3
WHERE
    MasterID  IS NULL

Answer 3

如果您只想选择，则可以使用以下查询 -

select recordid ,
       Att1,
       Att2,
       Att3,
       COALESCE( MasterID , (select min(a2.recordid) from tableA a2
                            where a2.Att1 = a1.Att1
                            and a2.Att2= a1.Att2
                            and a1.Att3 = a2.Att3))
from TableA a1

Answer 4

您可以使用交叉申请进行选择。 cross apply基本上选择匹配Att1，Att2和Att3的最低RecordID，并将RecordID作为名为MasteRID的列加入。

WITH temp as (SELECT RecordID, Att1, Att2, Att3, c.MasterID FROM dbo.TableA b
    CROSS APPLY (SELECT TOP 1 RecordID as MasterID 
    FROM dbo.TableA a 
    WHERE a.Att1=b.Att1 
    AND a.Att2=b.Att2 AND a.Att3=b.Att3 
    ORDER BY RecordID) c)

UPDATE TableA 
SET MasterID=t.MasterID
FROM temp t
WHERE RecordID=t.RecordID

更新将使用适当的RecordID更新每个RecordID条目的MasterID列。

SQL选择MAX查找组的单个记录

4 个答案: