登录注册数据库

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using static System.Console;
namespace WindowsFormsApp1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            try {
                DB.ConInit();
                string username = textBox1.Text.Trim();
                string password = textBox2.Text.Trim();
                if ((username == "") || (password == ""))
                {
                    MessageBox.Show("用户名或密码不能为空");
                }
                else
                {
                    string sqlm = "Select count(*) from PERSONS where USERNAME='";//""表示字符串，‘’表示值。
                    sqlm += username;
                    sqlm += "' ";
                    sqlm += "and PASSWORD=";
                    sqlm += "'";
                    sqlm += password;
                    sqlm += "'";
                    DB.Ds.Clear();
                    string ee = "eee";
                    DB.selectData(sqlm, ee);
                    string q = DB.Ds.Tables[ee].Rows[0][0].ToString();
                    int num = int.Parse(q);
                    //int num = int.Parse(DB.Ds.Tables["x"].Rows[0][0].ToString());
                    MessageBox.Show(num.ToString());
                    if (num == 1)
                    {
                        this.Hide();
                        var ssss = new Form2();
                        ssss.ShowDialog();
                        this.Close();
                       

                    }
                    else
                    {
                        MessageBox.Show("用户名或密码错误！！！");
                    }

                }
            }
            catch (Exception rr)
            {
                MessageBox.Show(rr.Message);
            }
            finally {

            }
            
        }

        private void button2_Click(object sender, EventArgs e)
        {
           
            string username = textBox1.Text.Trim();
            string password = textBox2.Text.Trim();
            if ((username == "") || (password == ""))
            {
                MessageBox.Show("用户名或密码不能为空！！！");
                return;
            }
            string sql = "select count(*) from PERSONS where USERNAME='";
            sql += username;
            sql += "'";
            DB.ConInit();
            DB.selectData(sql,"check");
            int num = int.Parse(DB.Ds.Tables["check"].Rows[0][0].ToString());
            if (num != 0)
            {
                MessageBox.Show("当前用户名已占用");
                
            }
            else {

                //string sql1 = " insert password from PERSONS where PASSWORD='";
                //sql1 += password;
                //sql1 += "'";
                string sqlx = "insert into PERSONS(USERNAME,PASSWORD) values('";
                sqlx += username;
                sqlx += "','";
                sqlx += password;
                sqlx += "')";
                string s = string.Empty;
                DB.insertData(sqlx,out s);
                MessageBox.Show(s);

                MessageBox.Show("注册成功");
            }
            WriteLine(num);
        }
    }
}