In the login screen to achieve a username and password to check, prompted empty

private void Button1_Click(object sender, EventArgs e)
        {
            string id = textBox1.Text.Trim().ToString();
            string pw = textBox2.Text.Trim().ToString();
            if (id == null || id.Length == 0 || pw == null || pw.Length == 0) {
                MessageBox.Show ( "user name or password can not be empty!");
                return;
            }
            string connectionstring = "Data Source = D:\\sqlite\\db823.db";
            SQLiteConnection connection = new SQLiteConnection(connectionstring);
            connection.Open();
            string sql = "select * from password where id = \"" + id + "\"";
            SQLiteDataAdapter da = new SQLiteDataAdapter(sql, connection);
            DataSet ds = new DataSet();
            if (da != null) {
                da.Fill(ds);

                DataTable dt = ds.Tables[0];
                if (dt == null || dt.Rows == null || dt.Rows.Count == 0 || dt.Rows[0][1] == null || !dt.Rows[0][1].Equals(pw))
                {
                                         MessageBox.Show ( "passwords do not match, please try again");
                    return;
                }
                else
                {
                                         MessageBox.Show ( "matching password");
                    Form2 form2 = new Form2();
                    form2.Show();
                    this.Hide();
                }
            }
        }

todo:
1, the package database-related class of operation
2, data structures SQLiteDataAdapter, DataSet, DataTable particular API are not very familiar (== null determination of these I silent)

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