Average by group in mysql database ASP.NET

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ASP.NET

MySQL

C#5.0

I want to obtain the average by group in a mysql database and grapg them in a chart.
I am able to group the items in the db and graph, but when I use the avg function on a column, I get column not found exception.
Can someone please help?
Thanks.

What I have tried:

public void GetData()
    {
        String constr = System.Configuration.ConfigurationManager.ConnectionStrings["web"].ToString();
        //MySqlConnection con = new MySqlConnection(constr);

        using (MySqlConnection con = new MySqlConnection(constr))
        {
            MySqlCommand cmd = new MySqlCommand("select " + col1.Text.ToString() + ", AVG(" + col2.Text.ToString() + ") from avance_presupuestario group by "+col1.Text, con);
            //Series s = Chart1.Series["Series1"];
            Series series = Chart1.Series["Series1"];
            con.Open();
            MySqlDataReader rdr = cmd.ExecuteReader();
            while (rdr.Read())
            {
                series.Points.AddXY(rdr[col1.Text].ToString(), rdr[col2.Text].ToString());
                //this.Chart1.Series["Series1"].Points.AddXY(rdr.GetString(col1.Text), rdr.GetInt32(col2.Text));
            }
        }
    }