Aspx for a 3 tire validation

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;

namespace test
{
    public partial class Student : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                hdnSTDID.Value = "Add";
            }
        }

        protected void btnSave_Click(object sender, EventArgs e)
        {
            string stdName = tbxName.Text;
            DBConnection dbConnection = new DBConnection();
            if (hdnMode.Value == "Add")
            {
                string sql = "INSERT INTO Student ([Name])  VALUES ('" + stdName + "')";
                dbConnection.ExecuteQuary(sql);

                string script = "alert(\"ADDfgfh..!\");";
                ScriptManager.RegisterStartupScript(this, this.GetType(),
                              "ServerControlScript", script, true);
            }
            if (hdnMode.Value == "Edit")
            {
                int stdId = int.Parse(hdnSTDID.Value);
                string sqlEdite = "UPDATE Student  SET Name = '" + stdName + "' WHERE StdId=" + stdId;
                dbConnection.ExecuteQuary(sqlEdite);
                hdnMode.Value = "Add";
                btnSave.Text = "Add";
            }
            gvStudent.DataBind();
            tbxName.Text = "";
        }

        protected void gvStudent_RowCommand(object sender, GridViewCommandEventArgs e)
        {
            int index = Convert.ToInt32(e.CommandArgument);
            string studentId = gvStudent.Rows[index].Cells[0].Text;
            int stdID = int.Parse(studentId);
            DBConnection con = new DBConnection();

            if (e.CommandName == "Del")
            {
                string strDelete = "DELETE FROM Student  WHERE StdId=" + stdID;

                con.ExecuteQuary(strDelete);
                gvStudent.DataBind();
            }
            if (e.CommandName == "Edi")
            {
                string sqlEdite = "SELECT  StdId, Name  FROM Student WHERE StdId=" + stdID;
                DataSet ds = con.GetData(sqlEdite);
                hdnSTDID.Value = ds.Tables[0].Rows[0]["StdId"].ToString();
                tbxName.Text = ds.Tables[0].Rows[0]["Name"].ToString();
                btnSave.Text = "Edite";
                hdnMode.Value = "Edit";
            }
        }
    }
}