如何防止表单重复提交？

	<form id="recordform" action="/record.php" name="recordform" method="post" target="id_frame1" autocomplete="off" onsubmit="return checkpost();">

						<h1>培训记录台账

						<span>请认真填写相关内容</span>

						</h1>

						<label>

						<span>部门 :</span>

						<select name="bumen" onChange="selectmokuai('bumen','keduimokuai','recordform');">

						<option value="" selected>  --请选择部门-- 

						</select>

						</label>

						<label>

						<span>科队/模块 :</span>

						<select name="keduimokuai">

					    <option value="" selected>--请选择科室/模块-- 

					    </select>

						</label>

						<label>

						<span id="xingming" name='xingming'>姓名 :</span>

						<input id="xingming" type="text" name="xingming" value=""></input>

			

						</label>

						<label>

						<span>培训时间 :</span>

						<input id="peixunshijian" type="text" name="peixunshijian" value="这里是要获取时间的！" readonly="true" ></input>

						</label>

						<label>

						<span>培训课题 :</span>

						<input id="keti" type="text" name="keti" value="网络与信息安全意识--教育活动" readonly="true"></input>

						</label>

						<label>

						<span>培训心得 :</span>

						<textarea id="xinde" name="xinde" value=""></textarea>

						</label>

						<label>

						<span> </span>

						<input id="button"  type="submit" class="button"  value="提交" style="cursor:pointer"/>

						</label>

					</form>

<?php

 

	$con = mysql_connect("localhost","root","w123456");

	if (!$con)

	  {

	  die('Could not connect: ' . mysql_error());

	  }



		mysql_select_db("peixunrecord", $con);

		mysql_query("set names 'utf8'");



	$bumen = $_POST['bumen'];

	$keduimokuai = $_POST['keduimokuai'];

	$xingming = $_POST['xingming'];

	$peixunshijian = $_POST['peixunshijian'];

	$keti = $_POST['keti'];

	$xinde = $_POST['xinde'];

	$sql="INSERT INTO record (bumen,keduimokuai,xingming,peixunshijian,keti,xinde) VALUES ('$bumen','$keduimokuai','$xingming','$peixunshijian','$keti','$xinde')";

	if (!mysql_query($sql,$con))

	  {

	  die('Error: ' . mysql_error());

	  }

	 echo "<script>alert('提交成功!');</script>";

	

	 //echo "提交成功 3秒后自动跳转";

	// echo "若没自动跳转，请点击<a href='javascript:history.go(-1)'>这里</a>返回";

	 //header("Refresh:5;url=http://www.baidu.com");

	mysql_close($con);

?>