Need to make scorboard in c#, how do i give winning team 3 points?

im making a WF where i get to insert soccer results, however the team winning should get 3, the losing team 0, if its a draw both should get 0.

i have a DB called voetbaldb, with a table called teams, where the scores of the teams should be updated, with 3 columns called ID which is primary key, teamname and teamrank which is unique.

so far i get to insert the results in the database into a different table called 'uitslagen' which is results just to clear it up.

this is my code, however i just cant get it work, i cant find away to give the winnning team the points it deserves:

      namespace SportApp
      {
       public partial class AddResults : Form
       {
        public AddResults()
        {
         InitializeComponent();
        }
         string connstring =  "Server=localhost;Port=3307;Database=voetbaldb;Uid=root;Pwd=usbw;";
    private void add_result_button_Click(object sender, EventArgs e)
    {
        try
        {
            string query = "INSERT INTO uitslagen (hometeam, awayteam, homescore, awayscore) VALUES ('" + txt_box_home_team.Text + "', '" + txt_box_away_team.Text + "', '" + txt_box_home_score.Text + "', '" + txt_box_away_score.Text + "')";
            MySqlConnection conn = new MySqlConnection(connstring);
            MySqlCommand cmd = new MySqlCommand(query, conn);

            conn.Open();

            MySqlDataReader reader = cmd.ExecuteReader();

            conn.Close();

            MessageBox.Show("The result has been added!");

            txt_box_home_team.Text = "";
            txt_box_away_team.Text = "";
            txt_box_home_score.Text = "";
            txt_box_away_score.Text = "";

        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.ToString());
        }

        if (txt_box_home_score.Text > txt_box_away_score.Text)
        {
            UPDATE teams SET teamrank = (SELECT ISNULL(MAX(teamrank), 0) + 1 FROM teams) 
        }
        if else (txt_box_home_score.Text < txt_box_away_score.Text)
        {
            UPDATE teams SET teamrank = (SELECT ISNULL(MAX(teamrank), 0) + 1 FROM teams) 
        }
        else (txt_box_home_score.Text == txt_box_away_score.Text)
            UPDATE teams SET teamrank = (SELECT ISNULL(MAX(teamrank), 0) + 1 FROM teams) 
            }

    }
}