我得到的Conversion from type 'DBNull' to type 'Integer' is not valid." error on the line "Dim avgObject As string = Cstr(avgCom.ExecuteScalar())
的DBNull到整数转换错误
命令的工作时,where module_ID='" & moduleSelect & "'
语句删除,我不知道如何解决这个问题,谁能帮助?
Dim moduleSelect As String = moduleRadio.SelectedValue
Using connection As New SqlConnection("Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\Database.mdf;Integrated Security=True;User Instance=True")
Using avgCom As New SqlCommand("SELECT AVG(exam) FROM completed_module where module_ID='" & moduleSelect & "' ", _
connection)
connection.Open()
Dim avgObject As Integer = CInt(avgCom.ExecuteScalar())
Dim averageVar As String
averageVar = avgObject.ToString
avgLabel.Text = averageVar
End Using
谷歌搜索'从类型'DBNull'转换为键入'整数'无效.'有近8000个结果。 – 2013-04-08 14:47:51
你可以运行查询'SELECT AVG(exam)..其中Module_ID = nnn'?我认为,它返回null,因为没有你传入的module_ID的记录。 – shahkalpesh 2013-04-08 14:49:14
当页面加载时没有从列表中选择任何值,从而给出null,谢谢大家的帮助。 – d99 2013-04-08 15:28:47