Hi guys i have 3 textboxes 1,2,3

textbox1 respresent mobileNo

textbox2 represent email

textbox3 represent roomno

I need to update any textboxes from three based on textchanged event

Suppose i need update room no in textbox3 changed event

room no is 22 i need to changed to 3333 then update in history by insert into statment in textchanged event

it make insert 4 times 

first time 3

second time 33

third time 333

four time 3333

how to prevent repeated insert into changes to history

public void UpdateMobileHistory(string ConnectionString,string SerialNo ,string
     EmployeeNo, string Mobile,string UserID,string DateEdit)
{
     SqlConnection con = new SqlConnection(ConnectionString);
     SqlCommand cmd = new SqlCommand();
     cmd.Connection = con;
     cmd.CommandType = CommandType.Text;
     cmd.CommandText = "insert into  dbo.HistoryEmployee
     values(@SerialNo,@EmployeeNo ,'Contact
     Data',@DateEdit,@UserID,@Mobile,null,null)";
     cmd.Parameters.Add("@SerialNo", SqlDbType.NVarChar, 20);
     cmd.Parameters.Add("@EmployeeNo", SqlDbType.NVarChar ,20);
     cmd.Parameters.Add("@Mobile", SqlDbType.NVarChar, 50);
     cmd.Parameters.Add("@UserID", SqlDbType.NVarChar ,20);
     cmd.Parameters.Add("@DateEdit", SqlDbType.NVarChar ,50);
     cmd.Parameters["@SerialNo"].Value = SerialNo;
     cmd.Parameters["@EmployeeNo"].Value = EmployeeNo;
     cmd.Parameters["@Mobile"].Value = Mobile;
     cmd.Parameters["@UserID"].Value = UserID;
     cmd.Parameters["@DateEdit"].Value = DateEdit;
     con.Open();
     cmd.ExecuteNonQuery();
     con.Close();
     }
     -----------------
     public string MaxHistoryEmployee(string ConnectionString)
     {
     SqlConnection con = new SqlConnection(ConnectionString);
     SqlCommand cmd = new SqlCommand();
     cmd.Connection = con;
     cmd.CommandType = CommandType.Text;
     cmd.CommandText = "select max(SerialNo)+1 from
     dbo.HistoryEmployee";
     con.Open();
     string commit = Convert.ToString(cmd.ExecuteScalar());
     con.Close();
     return commit;
     }
     -----------------
     private void textBox1_TextChanged(object sender, EventArgs e)
     {
     FleetManagment.Fleet fleetContact1 = new FleetManagment.Fleet();
     string ID = fleetContact1.MaxHistoryEmployee("Data Source=" +
     value1 + ";Initial Catalog=" + value2 + ";User ID=" +
     value3 + ";Password=" + value4 + "");
     fleetContact1.UpdateMobileHistory("Data Source=" + value1 +
     ";Initial Catalog=" + value2 + ";User ID=" + value3 +
     ";Password=" + value4 + "",ID ,textBox4.Text,
     textBox1.Text,label6.Text,label10.Text);
     }

this is all my code