求助：asp.net使用textbox增加数据库数据显示成功但是数据库没有数据变化（纯小白毕设）

想实现gridview展示数据，下面textbox加button增加数据，连接了数据库，在textbox里输入数据后点添加，显示的添加成功但是回去看数据库并没有输入的记录。输入主键相同的会显示错误1，不输入点击会错误2.为什么有messagebox提示了添加信息成功了后台还是没有变化。

 public partial class table1 : System.Web.UI.Page
    {
        string connectionString = System.Configuration.ConfigurationManager.ConnectionStrings["ConnectionString"].ToString();    

        protected void Button1_Click(object sender, EventArgs e)
        {

            string concen = txt1.Text;
            string vconcen = txt2.Text;           
            string tyd = txt2.Text;
            string tys = txt2.Text;
            string peak = txt2.Text;
            string peaks = txt2.Text;
            string sqlcmd = "SELECT * FROM table1  WHERE concentration=" + concen+ "";
            SqlConnection conn = new SqlConnection(connectionString);
            conn.Open();           
            SqlCommand cmd = new SqlCommand(sqlcmd,conn);
            //cmd.Connection = conn;
            //cmd.CommandText = "SELECT * FROM table6.1  WHERE concentration=" + concen + "";

            try
            {

                if (cmd.ExecuteScalar() != null)
                {

                    MessageBox.Show("错误1");

                }
                else
                {

                    sqlcmd = "INSERT INTO table1 VALUES ('" + concen + "','" + vconcen + "','" + tyd + "' ,'" + tys + "','" + peak + "','" + peaks + "')";


                    if (cmd.ExecuteNonQuery() != 0)
                    {

                        MessageBox.Show("添加信息成功！");
                    }

                    else
                    {

                        MessageBox.Show("添加信息失败！");
                    }
                }

            }

            catch (Exception ex)
            {

                MessageBox.Show("错误2" + ex.ToString());
            }


                  conn.Close();
            }


        }
    }