private sub button_click() 
Dim Where As String = String.Empty

        Using MyConnection As SqlConnection = New SqlConnection()

            MyConnection.ConnectionString = ConfigurationManager.ConnectionStrings("MyConnectionString").ConnectionString
            Using MyCommand As SqlCommand = New SqlCommand()

                Dim sqlAdapter As New SqlDataAdapter()
                ' creo nuova tabella
                Dim Table As New DataTable()


                MyCommand.CommandType = CommandType.Text
                MyCommand.Connection = MyConnection

                MyCommand.Parameters.Clear()
                
                'inizio i parametri per i filtri
                If Not String.IsNullOrEmpty(ddlanno.SelectedValue.ToString) Then
                    MyCommand.Parameters.AddWithValue("@anno", ddlanno.SelectedValue.ToString)
                    Where = Where & " WHERE Anno = @anno "

                End If

                If Not String.IsNullOrEmpty(ddlcentro.SelectedValue.ToString) Then
                    MyCommand.Parameters.AddWithValue("@centro", ddlcentro.SelectedValue.ToString)
                    If Not String.IsNullOrEmpty(Where) Then

                        Where = Where & " AND Codcen = @centro "
                    Else
                        Where = Where & " WHERE   Codcen = @centro"
                    End If
                End If

               ' ....altri parametri

                If MyCommand.Parameters.Count = 0 Then
                    lblfiltri.Visible = True
                    lblfiltri.Text = "nessun filtro impostato"
                    Exit Sub
                Else
                    lblfiltri.Visible = False
                End If


                MyCommand.CommandText = " SELECT ..." & _
    " FROM  (SELECT ..." & _
    " ..." & Where & ") AS Tab1" & _
    " GROUP BY ..."

                Try

                    MyCommand.Connection.Open()
                    sqlAdapter = New SqlDataAdapter(MyCommand.CommandText, "Data Source=xx;Initial Catalog=xx;User ID=xx;Password=xx")
                    sqlAdapter.SelectCommand = MyCommand
                    sqlAdapter.Fill(Table)
                    
                    Session("Table") = Table

                    
                    GridView1.DataSource = Session("Table")

                    GridView1.DataBind()


                Catch ex As Exception
                    Console.WriteLine(ex.Message)
                End Try

                If GridView1.Rows.Count = 0 Then
                    lblrighe.Visible = True
                    lblrighe.Text = "nessun risultato per i criteri impostati"
                Else
                    lblrighe.Visible = False
                End If
            End Using
        End Using

    End Sub