How to Group by Column and Merge Multiple Rows into One with a Dynamic Number of Columns in SQL?

SQL Server dynamic column grouping and multi-row merging

Question:

In the database table, there are multiple rows of results for each TestType and WorkOrder combination. The goal is to group by TestType and merge the results into a single row, with each Result value in a separate column.

Solution:

Dynamic solutions are needed to handle an uncertain number of results. The following script can handle up to 100 results. More than 100 results, need to add more CROSS JOINs in CTE Tally.

<code class="language-sql">DECLARE @SQL nvarchar(MAX),
        @CRLF nchar(2) = NCHAR(13) + NCHAR(10),
        @MaxTally int;

SELECT @MaxTally = MAX(C)
FROM (SELECT COUNT(*) AS C
      FROM dbo.Result
      GROUP BY WorkOrder,
               TestType) R;

WITH N AS(
    SELECT N
    FROM (VALUES(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL))N(N)),
Tally AS(
    SELECT TOP (@MaxTally) ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) AS I
    FROM N N1, N N2) --100 行，更多行需要添加更多 N
SELECT @SQL = N'WITH RNs AS(' + @CRLF +
              N'    SELECT WorkOrder,' + @CRLF +
              N'           TestType,' + @CRLF +
              N'           Result,' + @CRLF +
              N'           ROW_NUMBER() OVER (PARTITION BY WorkOrder, TestType ORDER BY (SELECT NULL)) AS RN --ORDER BY 应为您的 ID/始终递增列' + @CRLF +
              N'    FROM dbo.Result)' + @CRLF +
              N'SELECT WorkOrder,' + @CRLF +
              N'       TestType,' + @CRLF +
              --由于不知道 SQL Server 版本，使用 FOR XML PATH
              STUFF((SELECT N',' + @CRLF +
                            CONCAT(N'       MAX(CASE RN WHEN ',T.I,N' THEN Result END) AS Result',T.I)
                     FROM Tally T
                     ORDER BY T.I ASC
                     FOR XML PATH(N''),TYPE).value('(./text())[1]','nvarchar(MAX)'),1,3,N'') + @CRLF +
              N'FROM RNs R' + @CRLF +
              N'GROUP BY WorkOrder,' + @CRLF +
              N'         TestType;';

PRINT @SQL; --您的好帮手。

EXEC sys.sp_executesql @SQL;</code>

Sample data:

<code class="language-sql">CREATE TABLE Result(WorkOrder varchar(10), TestType varchar(20), Result decimal(10,2));
INSERT INTO Result (WorkOrder, TestType, Result) VALUES 
('HP19002316','VitaminA', 10.3),
('HP19002316','VitaminA', 11.3),
('HP19002316','VitaminA', 12.3),
('HP19002316','VitaminB', 13.4),
('HP19002316','VitaminB', 14.4),
('HP19002316','VitaminC', 15.5),
('HP19002316','VitaminD', 17.0)</code>

Expected output:

<code>WorkOrder       TestType        Result1   Result2  Result3 
==========================================================
HP19002316      VitaminA        10.3        11.3    12.3    
HP19002316      VitaminB        13.4        14.4    NULL
HP19002316      VitaminC        15.5        NULL    NULL
HP19002316      VitaminD        17.0        NULL    NULL</code>

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