我的查询没有'；I don’我不想显示在我的文本框中

我做了两个查询，第一个他一直很好地显示，第二个几乎相同，他没有显示。。我从一个组合框中选择，他必须在文本框中显示姓名，但他在第二个文本框中第一次显示姓名后第二次显示id，我不知道出了什么问题

    private void comboBox3_SelectedIndexChanged(object sender, EventArgs e)
    {
        //1
            con.Open();
            cmd = new SqlCommand("SELECT a.naam FROM [dbo].activiteiten_in_reserveringen air, [dbo].activiteiten a , [dbo].reserveringen r ,[dbo].klanten k WHERE a.id = air.activiteit_id AND air.reservering_id = r.id AND k.id = r.klant_id", con);
            SqlDataReader myReader = cmd.ExecuteReader();
            string SUM;
            while (myReader.Read())
            {
                SUM = myReader.GetString(0);
                Console.WriteLine(SUM);
                tbbActiviteit.Text = SUM;
            }

            con.Close();
        //2
            con.Open();
            cmd = new SqlCommand("SELECT k.naam FROM [dbo].activiteiten_in_reserveringen air, [dbo].activiteiten a , [dbo].reserveringen r ,[dbo].klanten k WHERE a.id = air.activiteit_id AND air.reservering_id = r.id AND k.id = r.klant_id", con);
            SqlDataReader myReadera = cmd.ExecuteReader();
            string SUM2;
            while (myReadera.Read())
            {
                SUM2 = myReadera.GetString(0);
                Console.WriteLine(SUM2);
                tbbNaam.Text = SUM2;
            }

            con.Close();
    }