Question

我的代码有问题吗？我有一个＆＃34; 转换类型＆＃39; DBNull＆＃39;输入＆＃39; String＆＃39;无效＆＃34;错误。

调用的函数（GetNoofHoursOfTImeIn）：

Public Shared Function GetNoofHoursofTImeIn(ByVal search As String, ByVal dfrom As   DateTime, ByVal dto As DateTime) As DataTable
Dim dtoffenseinfo As New DataTable

If Not DBConnection.State = ConnectionState.Open Then       
    DBConnection.Open()
End If

Using cmd As New OleDbCommand
    cmd.Connection = DBConnection
    cmd.CommandText = _
            "SELECT SUM(No_of_Hour) AS THour FROM EmployeeAttendance " & _
            "WHERE EmployeeID = ? " & _
                "AND WorkingDate BETWEEN ? AND ?"
    cmd.Parameters.AddWithValue("?", search)
    cmd.Parameters.AddWithValue("?", dfrom.Date)
    cmd.Parameters.AddWithValue("?", dto.Date)
    Using adapter As New OleDbDataAdapter(cmd)
        adapter.Fill(dtoffenseinfo)
    End Using
End Using

DBConnection.Close()
Return dtoffenseinfo
End Function

代码背后：

 txtPresentDays.Text = ClsAttendance.GetNoofHoursofTImeIn(EmployeeID.Text, MyDateString, MyDateString2).Rows(0).Item("THour")

我知道这个错误很常见，但直到现在我还不知道我是如何或为什么会这样做的。

感谢任何启蒙！

Answer 1

当零记录与条件匹配时，您将获得空值。您可以使用iif函数将该值转换为零：

SELECT IIF(SUM(No_of_Hour) Is Null, 0, SUM(No_of_Hour)) ...

我的代码出了什么问题？

1 个答案: