将动态查询中的逻辑从 Access VBA 转换为 SQL Server 视图

Question

我正在将 Access 应用程序转换为 Web 应用程序，但我无法将此 vb/SQL 转换为视图。这似乎不是那么难的问题，但它真的让我陷入困境。

Public Function GetProjectNumber(ByVal HeaderID As Long) As String
    Dim retval As String
    Dim rst As New ADODB.Recordset
    Dim tempID As Long

On Error GoTo Err_Handler

    rst.Open "SELECT TransferID, ProjectID FROM dbo.tblProject WHERE HeaderID = " & HeaderID
    If Not (rst.EOF And rst.BOF) Then
        If IsNull(rst!TransferID) Then
            retval = rst!ProjectID
        Else
            tempID = rst!TransferID
            If rst.State = adStateOpen Then rst.Close
            rst.Open "SELECT ProjectID FROM dbo.tblProject WHERE HeaderID = " & tempID
            If rst.EOF And rst.BOF Then
                retval = "Transfer from ????"
            Else
                retval = "Transfer from " & rst!ProjectID
            End If
        End If
    End If

If rst.State = adStateOpen Then rst.Close

Exit_Handler:
    Set rst = Nothing
    GetProjectNumber = retval
    Exit Function

End Function

我尝试使用嵌套的case 语句，但不能将案例应用于返回的每一行。有没有办法用IIF 做到这一点？还是让它成为一个函数？

Answer 1

以下查询为表中的所有记录（即所有 HeaderID）模仿您的代码。

SELECT P1.HeaderID,
(CASE 
    WHEN P1.TransferID IS NULL THEN P1.ProjectID
    WHEN P2.ProjectID IS NULL THEN 'Transfer from ???' 
    ELSE "Transfer from " + P2.ProjectID
 END) AS Returns
FROM dbo.tblProject P1
LEFT JOIN dbo.tblProject P2 ON P1.TransferID = P2.HeaderID 

如果您从中创建 SQL 服务器视图，则可以使用特定的 HeaderID 轻松查询它，就像您在 VBA 子中所做的那样

SELECT Returns FROM the_view WHERE HeaderID='xxxxx'

它应该返回与您的过程完全相同的结果