高手进来看看怎么解决这问题？ 急

Question

设计的本意是：点击btnRegister按钮 就查找数据库是否有跟tbUserName相同若有提示 “该用户已存在，请重新输入用户名” 如没有相同则 可以注册。   高手帮忙看看哪里错了  我数据库是  id（自增长）UserName Password。
      private void btnRegister_Click(object sender, EventArgs e)
        {                bool isEmpty = Check();
                if (isEmpty == true)
                {
                    int count;
                    string same = string.Format("select count(*) from Users where UserName='{0}'", tbUserName.Text.Trim());
                    string sql = string.Format("insert into Users values('{0}','{1}')", tbUserName.Text.Trim(), tbPassword.Text.Trim());
                    SqlCommand samename = new SqlCommand(same, DBhelper.connection);
                    DBhelper.connection.Open();
                    count = samename.ExecuteNonQuery();
                    DBhelper.connection.Close();
                    if (count < 1)
                    {
                        SqlCommand cmd = new SqlCommand(sql, DBhelper.connection);
                        DBhelper.connection.Open();
                        count = cmd.ExecuteNonQuery();
                        DBhelper.connection.Close();
                        if (count == 1)
                        {                            MessageBox.Show("注册成功！");
                            this.Hide();
                            LForm.GetUserName(tbUserName.Text.Trim());
                            LForm.Show();
                        }
                    }
                    else
                    {
                        MessageBox.Show("该用户已存在，请重新输入用户名");
                        
                    }
                    }
                }

Answer 1

ExecuteNonQuery():执行SQL，返回一个整型变量，如果SQL是对数据库的记录进行操作，那么返回操作影响的记录条数
使用 int Count=(int)cmd.ExecuteScalar();

Answer 2

private void ZhuCeButton_Click(object sender, EventArgs e)
        {
            if (TesterIdTextBox.Text == "")
            {
                MessageBox.Show("账号不能为空");
                return;
            }
            else if (TesterNameTextBox.Text == "")
            {
                MessageBox.Show("实验员不能为空");
                return;
            }
            else if (PwdTextBox.Text == "")
            {
                MessageBox.Show("密码不能为空");
                return;
            }
            Maticsoft.Model.Tester a_tester = new Maticsoft.Model.Tester();            if (check.GetModel(TesterIdTextBox.Text) == null)
            {
              
                a_tester.TesterId = TesterIdTextBox.Text;
                a_tester.TesterName = TesterNameTextBox.Text;
                a_tester.TesterPwd = PwdTextBox.Text;
                check.Add(a_tester);
                UpdataGrid();            }
            else
            {
                MessageBox.Show("账号已被占用", "信息提示", MessageBoxButtons.OK);
            }
          
        }
这是我最近在搞的一些代码，你用三层架构，会简单很多的

Answer 3

这个用ajax，焦点离开时就连接数据库，查找是否已存在！