SqlConnection conn=new SqlConnection("Server=purana;Database=test;Integrated Security=SSPI");
            SqlCommand cmd=new SqlCommand();
            cmd.CommandText="Select * From user_info where user_name=@name";
            cmd.Connection=conn;
            cmd.Parameters.Add(new SqlParameter("@name",SqlDbType.VarChar,20));
            cmd.Parameters["@name"].Value=textBox1.Text;
            SqlDataAdapter ada=new SqlDataAdapter(cmd);
            DataSet ds=new DataSet();
            conn.Open();
            ada.Fill(ds,"user_info");
            DataTable dt=ds.Tables[0];
            if(dt.Rows.Count>0)
            {
                textBox3.Text=dt.Rows[0][0].ToString() + dt.Rows[0][1].ToString();
                if(dt.Rows[0]["user_password"].ToString().Trim()==textBox2.Text)
                    MessageBox.Show("登录成功");
                else
                    MessageBox.Show("密码错误");
            }
            else
                MessageBox.Show("没有此用户");
            conn.Close();