sql - 动态行数据入列

Question

我有一列有 100 行数据。我需要获得前 4 名，但我需要将其转换为列而不是行。像 Col1、Col2、Col3 和 Col4。

我努力了

SELECT 
    MAX (CASE 
            WHEN rss_name = 'BBC-Sports' 
               THEN rss_name 
         END) AS col1,
    MAX (CASE 
            WHEN rss_name = 'Talk Sports' 
               THEN rss_name 
         END) AS col2,
    MAX (CASE 
            WHEN rss_name = 'Sky Sports' 
               THEN rss_name 
         END) AS col3,
    MAX (CASE 
            WHEN rss_name = 'Crick Info' 
               THEN rss_name 
         END) AS col4 
FROM 
    RSS

但它只适用于静态值：

我需要

 Col1,   Col2,       Col3,      Col4
 Sports,Talk Sports,Sky Sports,Crick Info

但由于这不是恒定数据，它会发生变化，并且 Col 中的值会不断变化。

Answer 1

您可以使用派生表来设置列顺序，然后在其上使用条件聚合。

SELECT 
    MAX(CASE WHEN Col_Rn = 1 THEN Rss_Name END) AS Col1,
    MAX(CASE WHEN Col_Rn = 2 THEN Rss_Name END) AS Col2,
    MAX(CASE WHEN Col_Rn = 3 THEN Rss_Name END) AS Col3,
    MAX(CASE WHEN Col_Rn = 4 THEN Rss_Name END) AS Col4
FROM (
       SELECT    Rss_Name, 
                 Row_Number() OVER (ORDER BY Rss_Name) AS Col_Rn -- set your order here
       FROM      RSS
    ) t

Answer 2

你需要使用Dynamic Pivot. 但在你的情况下，除了你需要一个额外的列用于 Pivot 中的列名，例如COL_1, COL_2....

架构：（来自您的图像。如果您在文本中提供此示例数据会更好）。

CREATE TABLE #TAB (Rss_Name VARCHAR(50))

INSERT INTO #TAB
SELECT 'Sports'
UNION ALL
SELECT 'Talk Sports'
UNION ALL
SELECT 'Sky Sports'
UNION ALL
SELECT 'Crick Info'

现在准备您的动态查询，如下所示

DECLARE @SQL VARCHAR(MAX)='',@PVT_COL VARCHAR(MAX)='';

--Preparing Dynamic Column List 
SELECT @PVT_COL =@PVT_COL
+ '[COL_'+CAST(ROW_NUMBER() OVER(ORDER BY (SELECT 1)) AS VARCHAR(4))+'],'
FROM #TAB
SELECT @PVT_COL = LEFT(@PVT_COL,LEN(@PVT_COL)-1)


SELECT @SQL = 
'SELECT * FROM (
SELECT Rss_Name
,''COL_''+CAST(ROW_NUMBER() OVER(ORDER BY (SELECT 1)) AS VARCHAR(4)) AS COL_NME 
FROM #TAB
)AS A
PIVOT
(
    MAX(Rss_Name) FOR COL_NME IN ('+@PVT_COL+')
)PVT'

EXEC (@SQL)

结果：

+--------+-------------+------------+------------+
| COL_1  |    COL_2    |   COL_3    |   COL_4    |
+--------+-------------+------------+------------+
| Sports | Talk Sports | Sky Sports | Crick Info |
+--------+-------------+------------+------------+