PIVOT 语句中的 SQL 子字符串问题

Question

我有一个非常大的表（100 多个字段），我需要在其中比较两条记录。为此，我决定使用 PIVOT。记录将由用户选择（因此它们将是动态的），但现在我将它们作为静态放入。

我的 SQL 如下所示：

-- Where clause params
DECLARE @whereClauseParam VARCHAR(MAX) = '[42] <> [600]' --<-- User will need to determine what the condition will be

--Get the Fields required for the initial pivot
DECLARE @Fields VARCHAR(MAX)= '';

SELECT @Fields+=QUOTENAME(t.name)+', '
FROM sys.columns AS t
WHERE t.object_id = OBJECT_ID('tblSQLAdminInventory')
    AND t.name <> 'TransID'
    AND t.system_type_id = '60';
--36
--48
--52
--56
--60
--61
--62
--104
--106
--127
--165
--167
--231
--239


-- Get the KeyId's with alias added
DECLARE @keyIDs VARCHAR(MAX)= '';

SELECT @keyIDs+=QUOTENAME(t.TransID)+' AS [KeyID_'+CAST(t.TransID AS VARCHAR(10))+'], '
FROM tblSQLAdminInventory AS t
WHERE TransID IN ('42', '600');

-- Get the KeyId's without alias
DECLARE @keyIDs1 VARCHAR(MAX)= '';

SELECT @keyIDs1+=QUOTENAME(t.TransID)+', '
FROM tblSQLAdminInventory AS t
WHERE TransID IN ('42', '600');

--Generate Dynamic SQL
DECLARE @SQL2 VARCHAR(MAX)= 'SELECT Value AS FieldName, ';

PRINT @SQL2+SUBSTRING(@keyIDs, 1, LEN(@keyIDs)-1)
PRINT @keyIDs
PRINT LEN(@keyIDs)

SELECT @SQL2+=SUBSTRING(@keyIDs, 1, LEN(@keyIDs)-1)+'
FROM
(SELECT TransID , Value , FieldName
FROM 
   (SELECT TransID,'+SUBSTRING(@Fields, 1, LEN(@Fields)-1)+'
   FROM tblSQLAdminInventory) p
UNPIVOT
   (FieldName  FOR Value IN 
      ('+SUBSTRING(@Fields, 1, LEN(@Fields)-1)+')
)AS unpvt) AS SourceTable
PIVOT
(
MAX(FieldName)
FOR TransID IN ('+SUBSTRING(@keyIDs1, 1, LEN(@keyIDs1)-1)+')
) AS PivotTable
--WHERE '+@whereClauseParam

PRINT(@SQL2);
EXECUTE(@SQL2);

我的 PIVOT 上方的 3 个 PRINT 行打印如下：

SELECT Value AS FieldName, [42] AS [KeyID_42], [600] AS [KeyID_600]
[42] AS [KeyID_42], [600] AS [KeyID_600], 
41

一切看起来都很好。但是，我的 PIVOT 上有一个错误：

Msg 537, Level 16, State 5, Line 49
Invalid length parameter passed to the LEFT or SUBSTRING function.
SELECT Value AS FieldName, 
Msg 102, Level 15, State 1, Line 1
Incorrect syntax near ','.

谁能告诉我为什么我的 PRINT 语句可以识别所有 3 个字段名称，但我的 PIVOT 语句不能？

奖励问题：当我过滤 t.system_type_id = '56' 时，它会返回数据。对于任何其他 system_type_id，我都会收到错误消息，并且没有返回任何记录。

编辑

根据要求，这是运行时没有错误的 SQL2：

SELECT Value AS FieldName, [42] AS [KeyID_42], [600] AS [KeyID_600]
FROM
(SELECT TransID , Value , FieldName
FROM 
   (SELECT TransID,[ErisaPlanEndsMM], [ErisaPlanEndsDD], [MLRAvgLivesNumber], [MLRAvgLivesRptYear]
   FROM tblSQLAdminInventory) p
UNPIVOT
   (FieldName  FOR Value IN 
      ([ErisaPlanEndsMM], [ErisaPlanEndsDD], [MLRAvgLivesNumber], [MLRAvgLivesRptYear])
)AS unpvt) AS SourceTable
PIVOT
(
MAX(FieldName)
FOR TransID IN ([42], [600])
) AS PivotTable
--WHERE [42] <> [600]

Answer 1

不确定这是否能解决您的所有问题，但您可以使用它来构建您的 @keyIds 并消除对 Substring() 的需要

-- Get the KeyId's with alias added
DECLARE @keyIDs VARCHAR(MAX),       
        @keyIDs1 VARCHAR(MAX);

SELECT  @keyIDs = COALESCE(@keyIDs + ',','') + QUOTENAME(t.TransID) + ' AS [KeyID_' + CAST(t.TransID AS VARCHAR(10)) + ']',
        @keyIDs1 = COALESCE(@keyIDs1 + ',','') + QUOTENAME(t.TransID)
FROM    tblSQLAdminInventory AS t
WHERE   TransID IN ('42', '600');