private void UpdateChart()
        {
            DataTable data;
            string Scholen;
            string Wijken;
            string diefstal;
            chart2.Titles.Clear();
            chart2.Series[0].Points.Clear();
            chart2.Series[0].Name = "Diefstallen per wijk";

            //Check if there is an input for niveau which can be converted to string. If this isn't the case set station to 'null'
            try
            {
                Scholen = Cbx_Niveau.SelectedItem.ToString();

            }
            catch
            {
                Scholen = null;
            }

            //Check if there is an input for wijk which can be converted to string. If this isn't the case set station to 'null'
            try
            {
                Wijken = Cbx_Wijk.SelectedItem.ToString();
            }
            catch
            {
                Wijken = null;
            }

            //Check if there is an input for diefstal which can be converted to string. If this isn't the case set station to 'null'
            try
            {
                diefstal = Cbx_Diefstal.SelectedItem.ToString();
            }
            catch
            {
                diefstal = null;
            }

            //Fill data with the read
            data = ReadQuery(Scholen, Wijken, diefstal);
            //Fill the chart with data from the induvidual rows.
            foreach (DataRow row in data.Rows)
            {

                Console.WriteLine(row[0] + " " + row[1]);
                chart2.Series[0].Points.AddXY(row[0], row[1]);
            }
        }

        private DataTable ReadQuery(string Cbx_Scholen, string Cbx_Wijk, string Cbx_Diefstal)
        {
            //check if the inputs are 'null'
            bool ScholenCheck = Cbx_Scholen == null,
                WijkCheck = Cbx_Wijk == null,
                DiefstalCheck = Cbx_Diefstal == null;

            string[] ColumnName = "Stations namen, wijken, Diefstallen".Split(',');
            if (ScholenCheck || WijkCheck || DiefstalCheck)
            {
                // per halte laten zien hoeveel diefstallen er zijn geweest
                // kunnen filteren op haltes en soort diefstal

                // alles weergeven van 1 niveau
                if (!ScholenCheck)
                {
                    return ReadSql("select scholen.niveau,count(misdaad.*) from misdaad join straatnaam on misdaad.jaartal = " +
                      "straatnaam.jaartal join station on station.code = komtAan.station where station.naam ='" + Cbx_Scholen + "'group by scholen.niveau order by scholen.niveau", ColumnName);
                }
                // alles weergeven van 1 wijk
                else if (!WijkCheck) return ReadSql("", ColumnName);
                // alles weergeven van 1 diefstal↓
                else if (!DiefstalCheck) return ReadSql("select station.naam, count(misdaad.*) from misdaad join komtAan on misdaad.jaartal = " +
                    "komtAan.jaartal join station on station.code = komtAan.station where misdaad.type = '" + Cbx_Diefstal + "' group by station.naam order by station.naam", ColumnName);
                // alles weergeven↓
                else return ReadSql("select station.naam, count(misdaad.*) from misdaad join komtAan on misdaad.jaartal = " +
                    "komtAan.jaartal join station on station.code = komtAan.station group by station.naam order by station.naam", ColumnName);
            }
            else
            {
                return ReadSql("select station.naam, count(misdaad.*) from misdaad join komtAan on misdaad.jaartal = " +
                    "komtaan.jaartal join station on station.code = komtaan.station where misdaad.type = '" + Cbx_Diefstal + "' and station.naam = '" + Cbx_Scholen + "' " +
                    "group by station.naam order by station.naam", ColumnName);
            }
        }

        static public DataTable ReadSql(string statement, string[] columnName)
        {
            var connString = "Host=localhost;Username=postgres;Password=0e654eaf;Database=Project 3";
            DataTable datastore = new DataTable();
            var conn = new NpgsqlConnection(connString);
            {
                for (int i = 0; i < columnName.Length; i++)
                {
                    datastore.Columns.Add(columnName[i]);
                }
                conn.Open();
                var cmd = new NpgsqlCommand(statement, conn);
                var reader = cmd.ExecuteReader();
                DataRow workRow;

                while (reader.Read())
                {
                    workRow = datastore.NewRow();
                    for (int i = 0; i < columnName.Length; i++)
                    {
                        workRow[i] = workRow[i] + reader.GetString(i);
                    }
                    datastore.Rows.Add(workRow);
                }
                conn.Close();
            }
            return datastore;
        }

        private void button2_Click(object sender, EventArgs e)
        {
            UpdateChart();
        }