//ktra dang nhap neu co tra ve ma vai tro public static string DangNhap(string tk, string mk) { string sql = string.Format("Select MaVaiTro from TAIKHOAN Where TenTaiKhoan = '{0}' and MatKhau = '{1}'", tk, mk); return(DL_LayDuLieu.ScalarKieuString(sql)); }