Filter comboBox (dependent to comboBox) mysql

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C#

MySQL

combobox

im trying to make a combobox filter depending from another combobox. its from two different tables in the same database. comboBox2 is already filled from type table. the next should display another value dpending on what you selected in the first combobox

this is the code for the combobox

MySqlConnection con = new MySqlConnection("datasource=localhost;port=3306;username=root;password=Deprisa!79849;");
       private void comboBox2_SelectedIndexChanged(object sender, EventArgs e)
       {
           //comboBox2,3,and 9
           comboBox3.SelectedIndex = -1;
           comboBox3.Items.Clear();
           if (con.State == ConnectionState.Closed)
           {
               con.Open();
           }

           MySqlCommand cmd = new MySqlCommand("Select Distinct(idbrand) from machine where idtype='" + comboBox2.SelectedItem + "'", con);

           MySqlDataReader rd = cmd.ExecuteReader();
           while (rd.Read())
           {
               comboBox3.Items.Add(rd[0]);
           }

           rd.Close();
           cmd.Dispose();



       }

       private void comboBox3_SelectedIndexChanged(object sender, EventArgs e)
       {
           comboBox9.SelectedIndex = -1;
           comboBox9.Items.Clear();

           if (con.State == ConnectionState.Closed)
           {
               con.Open();
           }

           MySqlCommand cmd = new MySqlCommand("select idmodel from machine where idtype='" + comboBox2.SelectedItem + "' and idmodel = '" + comboBox3.SelectedItem + "'", con);

           MySqlDataReader rd = cmd.ExecuteReader();

           while (rd.Read())
           {
               comboBox9.Items.Add(rd[0]);
           }
           rd.Close();
           cmd.Dispose();
       }