标量值声明错误

Question

我一直在尝试将SQLcmd参数用于我的代码：

Dim Conn As SqlConnection = New SqlConnection(MSSQLstring)
    Conn.Open()

    Dim strUserCode = CType(Session("usrCd"), String)

    Dim SQLstring As String

    If strUserCode = "ADMIN" Then
        SQLstring = "SELECT COUNT(AskAOID) AS credits, CatCode AS category, ProductCode " _
                                & "FROM dbo.AskAO_Stats " _
                                & "WHERE (FirstResponse BETWEEN @dateFrom; AND @dateTo;) " _
                                & "AND (Status='ACTIVE' OR Status='CLOSED') " _
                                & "AND (FirstResponse IS NOT NULL) AND (CatCode IS NOT NULL) AND (ProductCode IS NOT NULL) " _
                                & "GROUP BY ProductCode, CatCode " _
                                & "ORDER BY CatCode"
    Else
        SQLstring = "SELECT COUNT(AskAOID) AS credits, CatCode AS category, ProductCode " _
                                & "FROM dbo.AskAO_Stats " _
                                & "WHERE (FirstResponse BETWEEN @dateFrom; AND @dateTo;) " _
                                & "AND (Status='ACTIVE' OR Status='CLOSED') " _
                                & "AND (Deferred = '" & strUserCode & "') " _
                                & "AND (FirstResponse IS NOT NULL) AND (CatCode IS NOT NULL) AND (ProductCode IS NOT NULL) " _
                                & "GROUP BY ProductCode, CatCode " _
                                & "ORDER BY CatCode"
    End If

    Dim SQLcmd As SqlCommand = New SqlCommand(SQLstring, Conn)
    SQLcmd.Parameters.AddWithValue("@dateFrom", dpFrom.SelectedDate.ToString)
    SQLcmd.Parameters.AddWithValue("@dateTo", dpTo.SelectedDate.ToString)
    Dim DA As New SqlDataAdapter(SQLstring, Conn)
    Dim DS As New DataSet
    DA.Fill(DS)

    Conn.Close()

dpFrom和dpTo是日期选择器，我试图消除我的SQL声明中的连接。不幸的是，从上面的代码中，我收到此错误消息：

必须声明标量变量“@dateFrom”。

到目前为止我还没有使用SQLcmd参数别名，所以我想知道我做错了什么：（

全部谢谢：）

更新

我也尝试了以下代码更改，但我没有运气:(

Dim Conn As SqlConnection = New SqlConnection(MSSQLstring)
    Conn.Open()

    Dim strUserCode = CType(Session("usrCd"), String)

    Dim SQLstring As String

    If strUserCode = "ADMIN" Then
        SQLstring = "SELECT COUNT(AskAOID) AS credits, CatCode AS category, ProductCode " _
                                & "FROM dbo.AskAO_Stats " _
                                & "WHERE (FirstResponse BETWEEN @dateFrom AND @dateTo) " _
                                & "AND (Status='ACTIVE' OR Status='CLOSED') " _
                                & "AND (FirstResponse IS NOT NULL) AND (CatCode IS NOT NULL) AND (ProductCode IS NOT NULL) " _
                                & "GROUP BY ProductCode, CatCode " _
                                & "ORDER BY CatCode"
    Else
        SQLstring = "SELECT COUNT(AskAOID) AS credits, CatCode AS category, ProductCode " _
                                & "FROM dbo.AskAO_Stats " _
                                & "WHERE (FirstResponse BETWEEN @dateFrom AND @dateTo) " _
                                & "AND (Status='ACTIVE' OR Status='CLOSED') " _
                                & "AND (Deferred = '" & strUserCode & "') " _
                                & "AND (FirstResponse IS NOT NULL) AND (CatCode IS NOT NULL) AND (ProductCode IS NOT NULL) " _
                                & "GROUP BY ProductCode, CatCode " _
                                & "ORDER BY CatCode"
    End If

    Dim SQLcmd As SqlCommand = New SqlCommand(SQLstring, Conn)
    SQLcmd.Parameters.AddWithValue("@dateFrom", dpFrom.SelectedDate)
    SQLcmd.Parameters.AddWithValue("@dateTo", dpTo.SelectedDate) 
    Dim DA As New SqlDataAdapter(SQLstring, Conn)
    Dim DS As New DataSet
    DA.Fill(DS)

    Conn.Close()