是否可以使用临时列WHERE子句

Question

1. 我想在RequestStatus_hod为IN PROCESS
2. 但查询似乎显示所有的数据通过忽略where子句
3. 当你只显示数据可以看到，我试图重复WHERE RequestStatus_hod = 'IN PROCESS'但它只是显示为NULL
4. 我试图使用临时列RequestStatus_hods并获得an invalid column error

SQL语句：

SELECT DISTINCT 
    A.RequestNumber, A.EmployeeId, 
    STUFF((SELECT ', ' + CAST(B.RequestDetailsId AS VARCHAR(255)) 
      FROM [dbo].[REQUISITION] C 
      JOIN [dbo].[REQUISITION_DETAILS] B ON C.RequestDetailsId = B.RequestDetailsId 
      WHERE C.RequestNumber = A.RequestNumber AND C.EmployeeId = A.EmployeeId -- AND RequestStatus_hod = 'IN PROCESS' 
      FOR XML PATH ('')), 1, 2, '') AS RequestDetailIds, 
    STUFF((SELECT ', ' + CAST(B.StockId AS VARCHAR(255)) 
      FROM [dbo].[REQUISITION] C 
      JOIN [dbo].[REQUISITION_DETAILS] B ON C.RequestDetailsId = B.RequestDetailsId 
      JOIN [dbo].[STOCK] F ON F.StockId = B.StockId 
      WHERE C.RequestNumber = A.RequestNumber AND C.EmployeeId = A.EmployeeId -- AND RequestStatus_hod = 'IN PROCESS' 
      FOR XML PATH ('')), 1, 2, '') AS StockIds, 
    STUFF((SELECT ', ' + CAST(B.RequestQuantity AS VARCHAR(255)) 
      FROM [dbo].[REQUISITION] C 
      JOIN [dbo].[REQUISITION_DETAILS] B ON C.RequestDetailsId = B.RequestDetailsId 
      WHERE C.RequestNumber = A.RequestNumber AND C.EmployeeId = A.EmployeeId -- AND RequestStatus_hod = 'IN PROCESS' 
      FOR XML PATH ('')), 1, 2, '') AS RequestQuantity, 
    STUFF((SELECT ', ' + G.ItemName 
      FROM [dbo].[REQUISITION] C 
      JOIN [dbo].[REQUISITION_DETAILS] B ON C.RequestDetailsId = B.RequestDetailsId 
      JOIN [dbo].[STOCK] F ON F.StockId = B.StockId 
      JOIN [dbo].[ITEM_MASTER] G ON F.ItemId = G.ItemId 
      WHERE C.RequestNumber = A.RequestNumber AND C.EmployeeId = A.EmployeeId -- AND RequestStatus_hod = 'IN PROCESS' 
      FOR XML PATH ('')), 1, 2, '') AS ItemNames, 
    STUFF((SELECT ', ' + CAST(F.StockQuantity AS VARCHAR(255)) 
      FROM [dbo].[REQUISITION] C 
      JOIN [dbo].[REQUISITION_DETAILS] B ON C.RequestDetailsId = B.RequestDetailsId 
      JOIN [dbo].[STOCK] F ON F.StockId = B.StockId 
      WHERE C.RequestNumber = A.RequestNumber AND C.EmployeeId = A.EmployeeId -- AND RequestStatus_hod = 'IN PROCESS' 
      FOR XML PATH ('')), 1, 2, '') AS AvailableQuantity, 
    STUFF((SELECT ', ' + B.RequestStatus_hod 
      FROM [dbo].[REQUISITION] C 
      JOIN [dbo].[REQUISITION_DETAILS] B ON C.RequestDetailsId = B.RequestDetailsId 
      WHERE C.RequestNumber = A.RequestNumber AND C.EmployeeId = A.EmployeeId -- AND RequestStatus_hod = 'IN PROCESS' 
      FOR XML PATH ('')), 1, 2, '') AS RequestStatus_hods -- Temporary Column -- 
FROM 
    [dbo].[REQUISITION] A 
JOIN 
    [dbo].[USER] D ON D.EmployeeId = A.EmployeeId 
JOIN 
    [dbo].[REQUISITION_DETAILS] E ON E.EmployeeId = D.EmployeeId 
WHERE 
    RequestStatus_hods = 'IN PROCESS' -- Col RequestStatus_hod FROM table REQUISITION_DETAILS -- 

结果：

Answer 1

一种解决方案是重复WHERE子句中的临时列的定义。 SQL Server不支持直接在WHERE中使用别名，但它仍然足够智能（在大多数情况下）可以确定不需要对表达式进行两次评估。因此，不要在WHERE中写入RequestStatus_hod = 'IN PROCESS'，而要将该列的实际定义复制并粘贴到RequestStatus_hods的位置。

但是，更好的选择可能是将您的列提取到APPLY子句中。这样，你肯定知道它不会运行两次。

例如：

SELECT DISTINCT 
    A.RequestNumber, A.EmployeeId, 
    STUFF((SELECT ', ' + CAST(B.RequestDetailsId AS VARCHAR(255)) 
      FROM [dbo].[REQUISITION] C 
      JOIN [dbo].[REQUISITION_DETAILS] B ON C.RequestDetailsId = B.RequestDetailsId 
      WHERE C.RequestNumber = A.RequestNumber AND C.EmployeeId = A.EmployeeId -- AND RequestStatus_hod = 'IN PROCESS' 
      FOR XML PATH ('')), 1, 2, '') AS RequestDetailIds, 
    STUFF((SELECT ', ' + CAST(B.StockId AS VARCHAR(255)) 
      FROM [dbo].[REQUISITION] C 
      JOIN [dbo].[REQUISITION_DETAILS] B ON C.RequestDetailsId = B.RequestDetailsId 
      JOIN [dbo].[STOCK] F ON F.StockId = B.StockId 
      WHERE C.RequestNumber = A.RequestNumber AND C.EmployeeId = A.EmployeeId -- AND RequestStatus_hod = 'IN PROCESS' 
      FOR XML PATH ('')), 1, 2, '') AS StockIds, 
    STUFF((SELECT ', ' + CAST(B.RequestQuantity AS VARCHAR(255)) 
      FROM [dbo].[REQUISITION] C 
      JOIN [dbo].[REQUISITION_DETAILS] B ON C.RequestDetailsId = B.RequestDetailsId 
      WHERE C.RequestNumber = A.RequestNumber AND C.EmployeeId = A.EmployeeId -- AND RequestStatus_hod = 'IN PROCESS' 
      FOR XML PATH ('')), 1, 2, '') AS RequestQuantity, 
    STUFF((SELECT ', ' + G.ItemName 
      FROM [dbo].[REQUISITION] C 
      JOIN [dbo].[REQUISITION_DETAILS] B ON C.RequestDetailsId = B.RequestDetailsId 
      JOIN [dbo].[STOCK] F ON F.StockId = B.StockId 
      JOIN [dbo].[ITEM_MASTER] G ON F.ItemId = G.ItemId 
      WHERE C.RequestNumber = A.RequestNumber AND C.EmployeeId = A.EmployeeId -- AND RequestStatus_hod = 'IN PROCESS' 
      FOR XML PATH ('')), 1, 2, '') AS ItemNames, 
    STUFF((SELECT ', ' + CAST(F.StockQuantity AS VARCHAR(255)) 
      FROM [dbo].[REQUISITION] C 
      JOIN [dbo].[REQUISITION_DETAILS] B ON C.RequestDetailsId = B.RequestDetailsId 
      JOIN [dbo].[STOCK] F ON F.StockId = B.StockId 
      WHERE C.RequestNumber = A.RequestNumber AND C.EmployeeId = A.EmployeeId -- AND RequestStatus_hod = 'IN PROCESS' 
      FOR XML PATH ('')), 1, 2, '') AS AvailableQuantity, 
    xx.RequestStatus_hods -- Temporary Column -- 
FROM 
    [dbo].[REQUISITION] A 
JOIN 
    [dbo].[USER] D ON D.EmployeeId = A.EmployeeId 
JOIN 
    [dbo].[REQUISITION_DETAILS] E ON E.EmployeeId = D.EmployeeId 
CROSS APPLY 
    (SELECT STUFF((SELECT ', ' + B.RequestStatus_hod 
      FROM [dbo].[REQUISITION] C 
      JOIN [dbo].[REQUISITION_DETAILS] B ON C.RequestDetailsId = B.RequestDetailsId 
      WHERE C.RequestNumber = A.RequestNumber AND C.EmployeeId = A.EmployeeId 
      FOR XML PATH ('')), 1, 2, '') as RequestStatus_hods) xx 
WHERE 
    xx.RequestStatus_hods = 'IN PROCESS' -- Col RequestStatus_hod FROM table REQUISITION_DETAILS -- 

Answer 2

尝试

WHERE E.RequestStatus_hod = 'IN PROCESS'

Answer 3

完全取出WHERE条款，并尝试这而不是

JOIN 
[dbo].[REQUISITION_DETAILS] E 
ON E.EmployeeId = D.EmployeeId 
AND E.RequestStatus_hod = 'IN PROCESS' 

Answer 4

好吧首先，让我们叫的东西与他们的名字，RequestStatus_hods是不是“临时列”，这是摆在查询的结果集的列与计算别名“RequestStatus_hods”。

我并不真正理解那些涉及CROSS JOINS的解决方案，所以我无法评估它们，但我估计在这些情况下性能并不是最好的。

我对这类问题有两种不同的方法 1.-而不是在where子句中的“RequestStatus_hods”，使用完全相同的表达式，您正在使用该表达式来构建列中的值。它会工作，但如果结果集包含大量记录，则性能将受到影响。 2：我包围查询如下

SELECT * FROM (<YOUR-QUERY>) AS 
RESULTSET WHERE RESULTSET.[RequestStatus_hods] = 'IN PROCESS' 

所以您的查询变为内，由临时表（取决于谁的引擎解析查询），但效果是，你必须要与表你想要的领域。这种方法的表现通常不是很糟糕。

希望这会有所帮助。