基于列值的透视，在多列中输出答案

【问题标题】：column value based pivot with output in multiple columns基于列值的透视，在多列中输出
【发布时间】：2021-06-27 22:35:24
【问题描述】：

我有一张桌子：

HostName	Application
SRV000001	App1
SRV000001	App2
SRV000002	App3
SRV000003	App1
SRV000003	App4
SRV000003	App5

我需要围绕主机名列进行旋转/分组，以便结果类似于。由于要获取的列数不固定，我发现很难在此上使用数据透视函数。

HostName	Col1	Col2	Col3
SRV000001	App1	App2
SRV000002	App3
SRV000003	App1	App4	App5

【问题讨论】：

标签： sql-server tsql pivot

【解决方案1】：

可以使用ROW_NUMBER() 窗口函数对列进行编号以确定列标题，例如Col1, Col2..，然后可以通过使用此查询应用条件聚合：

SELECT [HostName], 
       MAX(CASE WHEN [rn]=1 THEN [Application] END) AS [Col1],
       MAX(CASE WHEN [rn]=2 THEN [Application] END) AS [Col2],
       MAX(CASE WHEN [rn]=3 THEN [Application] END) AS [Col3]
  FROM( 
       SELECT *,
              ROW_NUMBER() OVER 
              (PARTITION BY [HostName] ORDER BY [Application]) AS [rn]
         FROM [t]
      ) AS t
 GROUP BY [HostName]

查询可能会通过以下代码块转换为动态查询：

DECLARE @cols  AS NVARCHAR(MAX),  @query AS NVARCHAR(MAX)

SET @cols = ( SELECT STRING_AGG('MAX(CASE WHEN [rn]='+
                                 CAST([rn] AS VARCHAR)+
                               ' THEN [Application] END) AS [Col'+
                                 CAST([rn] AS VARCHAR)+
                               ']',',') 
                FROM (SELECT DISTINCT ROW_NUMBER() OVER 
                            (PARTITION BY [HostName] ORDER BY [HostName]) AS [rn]
                        FROM [t] ) t );

SET  @query = 
     N'SELECT [HostName],' + @cols + 
     N'  FROM( 
              SELECT *,
                     ROW_NUMBER() OVER 
                     (PARTITION BY [HostName] ORDER BY [Application]) AS [rn]
                FROM [t]
             ) AS t
        GROUP BY [HostName]';

EXEC sp_executesql @query;

Demo

【讨论】：