将日期时间插入并更新到SQL数据库中

private void ButtonOk_Click(object sender, EventArgs e)
    {
        if (txtWedstrijdSchemaID.Text == "")
        {
            //Insert
            string SQL;
            SQL = "Insert into Wedstrijdschema (Team1, Team2, Datum)";
            SQL += " values (";
            SQL += "" + txtTeam1.Text + ",";
            SQL += "" + txtTeam2.Text + ",";
            SQL += "" + Convert.ToDateTime(txtDatum.Text) + "";
            SQL += ")";

            clDatabase.ExecuteCommand(SQL);
            vulLv();
        }
        else
        {
            //Update
            string SQL;
            SQL = "Update Wedstrijdschema SET ";
            SQL += "Team1 = " + txtTeam1.Text + ",";
            SQL += "Team2 = " + txtTeam2.Text + ",";
            SQL += "Datum = " + Convert.ToDateTime(txtDatum.Text) + "";
            SQL += " where SchemaId = " + zoek;

            clDatabase.ExecuteCommand(SQL);
            vulLv();
        }
        txtDatum.Enabled = txtTeam2.Enabled = txtTeam1.Enabled = false;
    }
private void ButtonOk_Click(object sender, Even