请问用脚本.bat导出数据库，结果没数据是什么原因？

执行以下代码：

@echo off

set "Ymd=%date:~,4%%date:~5,2%%date:~8,2%"
E:\wamp\mysql5.5.24\bin\mysqldump -u root -p agent > D:\db_backup\agent_%Ymd%.sql
 
@echo on

打开生成的sql文件，里面是这样的

-- MySQL dump 10.13  Distrib 5.5.24, for Win32 (x86)
--
-- Host: localhost    Database: agent
-- ------------------------------------------------------
-- Server version    5.5.5-10.1.14-MariaDB

/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;
/*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */;
/*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */;
/*!40101 SET NAMES utf8 */;
/*!40103 SET @OLD_TIME_ZONE=@@TIME_ZONE */;
/*!40103 SET TIME_ZONE='+00:00' */;
/*!40014 SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0 */;
/*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */;
/*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */;
/*!40111 SET @OLD_SQL_NOTES=@@SQL_NOTES, SQL_NOTES=0 */;

请问是什么原因？