ช่วยดูโค้ดให้หน่อยคับว่าทำไม รหัสไม่รัน Auto คับ VB2008 กับ MySQL

txtid.Text = LastID.ToString("M000")

txtid.Text =  "M" & LastID.ToString("000")

txtid.Text =  "M" & LastID.ToString("000")

Private Sub showcode()
        cn.Open()
        Dim sql As String = "SELECT * FROM mytable ORDER BY T_id DESC LIMIT 0,1"
        
        dt = New DataTable
        da = New MySqlDataAdapter(sql, cn)
        da.Fill(dt)

        If dt.Rows.Count > 0 Then

            Dim i As Integer = dt.Rows(0).Item("T_id") + 1
            txtid.Text = i.ToString("000#")
        Else
            txtid.Text = "0001"
        End If
    End Sub

Private Sub showcode()
        cn.Open()
        Dim sql As String = "SELECT * FROM mytable ORDER BY T_id DESC LIMIT 0,1"
        
        dt = New DataTable
        da = New MySqlDataAdapter(sql, cn)
        da.Fill(dt)

        If dt.Rows.Count > 0 Then

            Dim i As Integer = dt.Rows(0).Item("T_id") + 1
            txtid.Text = "M"+ i.ToString("000#")
        Else
            txtid.Text = "M"+"0001"
        End If
    End Sub

Private Sub AutoGenerateRun()
        Dim myConnection As MySqlConnection
        myConnection = New MySqlConnection("Database=testconn;Data Source=localhost;User Id=root;Password=root")
        myConnection.Open()
        Dim sqlTmp As String = ""
        Dim comTmp As MySqlCommand = New MySqlCommand
        Dim drTmp As MySqlDataReader
        Dim tmpID As String = ""

             Dim LastID As Integer = 0

        sqlTmp = "SELECT * FROM mytable ORDER BY T_id DESC LIMIT 0,1"
       

        

        Try
            With comTmp
                .CommandType = CommandType.Text
                .CommandText = sqlTmp
                .Connection = Conn
                drTmp = .ExecuteReader()
                drTmp.Read()

                tmpID = CStr(drTmp.Item("T_id"))
                LastID = CInt(StringFromRight(tmpID, 3))
                LastID = LastID + 1
                txtid.Text = "M"&LastID
                drTmp.Close()
            End With
        Catch
            txtid.Text = "M001"
        End Try

    End Sub

Private Sub AutoGenerateRun()
        Dim myConnection As MySqlConnection
        myConnection = New MySqlConnection("Database=testconn;Data Source=localhost;User Id=root;Password=root")
        myConnection.Open()
        Dim sqlTmp As String = ""
        Dim comTmp As MySqlCommand = New MySqlCommand
        Dim drTmp As MySqlDataReader
        Dim tmpID As String = ""

             Dim LastID As Integer = 0

        sqlTmp = "SELECT * FROM mytable ORDER BY T_id DESC LIMIT 0,1"
       

        

        Try
            With comTmp
                .CommandType = CommandType.Text
                .CommandText = sqlTmp
                .Connection = Conn
                drTmp = .ExecuteReader()   '<<<ดีบัคแล้วตรง drTmp มันไม่มีค่าเลยอะครับ 
                drTmp.Read()

                tmpID = CStr(drTmp.Item("T_id"))
                LastID = CInt(StringFromRight(tmpID, 3))
                LastID = LastID + 1
                txtid.Text = "M"&LastID
                drTmp.Close()
            End With
        Catch                    '<<<แล้วก็มารันตรงบรรทัดนี้เลยครับ
            txtid.Text = "M001"
        End Try

    End Sub

Private Sub auto_id()
        Dim sqlcmd As MySqlCommand = New MySqlCommand
        Dim dr As MySqlDataReader
        Dim tempSql As String = "SELECT * FROM mytable ORDER BY T_id DESC LIMIT 0,1"

        Dim tempId As String
        cn.Open()
        Try
            sqlcmd.CommandType = CommandType.Text
            sqlcmd.CommandText = tempSql
            sqlcmd.Connection = cn
            dr = sqlcmd.ExecuteReader
        Catch ex As Exception
            MessageBox.Show(ex.Message)
            Exit Sub
        End Try
        dr.Read()
        If IsDBNull(dr.Item("T_id")) = True Then    
            txtid.Text = "M" & "0001"
        Else
            tempId = dr.Item("T_id")
            txtid.Text = "M" & (tempId.Substring(3) + 1).ToString("0000")
        End If
        cn.Close()
    End Sub