how to give a message that record already exist in database

protected void Insert(object sender, EventArgs e)
        {
            string ConnectionString = WebConfigurationManager.ConnectionStrings["testConnectionString"].ConnectionString;
            SqlConnection sqlconnection = null;
          
        int retVal=0;
                TextBox cust_id = (TextBox)GridView1.FooterRow.FindControl("txtCustId");
 
                TextBox name = (TextBox)GridView1.FooterRow.FindControl("txtName");
 
                TextBox state = (TextBox)GridView1.FooterRow.FindControl("txtState");
 
                TextBox s_amount = (TextBox)GridView1.FooterRow.FindControl("txtAmnt");
 
                TextBox sales_id = (TextBox)GridView1.FooterRow.FindControl("txtSid");
 
                try
                {
 
                    using (sqlconnection = new SqlConnection(ConnectionString))
                    {
                        sqlconnection.Open();
                        SqlCommand cmd = new SqlCommand("GetSubmitDetails", sqlconnection);
                        cmd.CommandType = CommandType.StoredProcedure;
                        cmd.Parameters.Add("@cust_id", SqlDbType.Int).Value = cust_id.Text;
                        cmd.Parameters.Add("@name", SqlDbType.VarChar).Value = name.Text;
                        cmd.Parameters.Add("@state", SqlDbType.VarChar).Value = state.Text;
                        cmd.Parameters.Add("@s_amount", SqlDbType.VarChar).Value = s_amount.Text;
                        cmd.Parameters.Add("@sales_id", SqlDbType.Int).Value = sales_id.Text;
 
                        cmd.ExecuteNonQuery();
                      
                    }
                }
 
                catch (Exception ex)
                {
                    Console.WriteLine("Error reading from {0}", ex);
                }
                finally
                {
                    sqlconnection.Close();
                }
            
            if (retVal == 2)
            {
                  ScriptManager.RegisterStartupScript(this.Page, this.GetType(), "Alert","alert('Record Exists !!!');", true);
            }
            else
            {
            GridView1.EditIndex = -1;
           ScriptManager.RegisterStartupScript(this.Page, this.GetType(), "Alert","alert('Record Saved Sucessfully');", true);
            GridView1.DataBind();
            GetData();
            }
       
    }
 
    
 
        protected void GridView1_PageIndexChanging(object sender, GridViewPageEventArgs e)
        {
            GridView1.PageIndex = e.NewPageIndex;
            GetData();
        }
 
        protected void GridView1_RowDeleting(object sender, GridViewDeleteEventArgs e)
        {
 
            string cust_id = GridView1.DataKeys[e.RowIndex].Value.ToString();
            string sales_id = GridView1.DataKeys[e.RowIndex].Value.ToString();
            GridViewRow row = (GridViewRow)GridView1.Rows[e.RowIndex];
           
            string ConnectionString = WebConfigurationManager.ConnectionStrings["testConnectionString"].ConnectionString;
            SqlConnection sqlconnection = null;
            try
            {
 
                using (sqlconnection = new SqlConnection(ConnectionString))
                {
                
                    sqlconnection.Open();
                  
                    SqlCommand cmd = new SqlCommand("GetDeleteItems", sqlconnection);
                    cmd.CommandType = CommandType.StoredProcedure;
                    cmd.Parameters.Add("@cust_id", SqlDbType.Int).Value = cust_id as String;
                    cmd.Parameters.Add("@sales_id", SqlDbType.Int).Value = sales_id as String;
                  
 
                  
 
                    SqlDataAdapter adapter = new SqlDataAdapter(cmd);
                    cmd.ExecuteNonQuery();
                   
                    ScriptManager.RegisterStartupScript(this.Page, this.GetType(), "Alert","alert('Record Deleted Sucessfully');", true);
                    GetData();
                   
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine("Error reading from {0}", ex);
            }
            finally
            {
                sqlconnection.Close();
            }
         
        }