基于现有列数据创建列，重复数据存在

Question

我有这样的一个表：

Acct MasterAcct 
------- ------------- 
123  M01 
123  M02 
234  M03 
345  M04 
456  M05 
456  M06 
456  M07 

我想打破MasterAcct列到三列（Master1，Master2，为主设备）。一个帐户最多可以有三个与之关联的主帐户。上一个表的示例输出将在一行上具有账号＃456，然后在Master1，Master2和Master3中具有三个主账号。谁能帮忙？

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Answer 1

您可以结合使用PIVOT与ROW_NUMBER()排名功能。

SELECT Acct, [1] as [Master1], [2] as [Master2], [3] as [Master3] 
FROM 
    (
     SELECT Acct, 
      MasterAcct, 
      ROW_NUMBER() OVER(PARTITION BY acct ORDER BY MasterAcct) as mid 
     FROM tbl 
    ) as t 
PIVOT 
(
    MIN(MasterAcct) 
    FOR mid IN ([1], [2], [3]) 
) as p 

SQL FIDDLE DEMO

可以实现在不使用PIVOT相同的结果。以下查询很容易理解。

SELECT 
    Acct, 
    MAX(CASE WHEN mid=1 THEN MasterAcct END) as [Master1], 
    MAX(CASE WHEN mid=2 THEN MasterAcct END) as [Master2], 
    MAX(CASE WHEN mid=3 THEN MasterAcct END) as [Master3] 
FROM 
    (
     SELECT Acct, 
      MasterAcct, 
      ROW_NUMBER() OVER(PARTITION BY acct ORDER BY MasterAcct) as mid 
     FROM tbl 
    ) t 
GROUP BY Acct 

SQL FIDDLE DEMO