PHP提交表单到当前页动作检测

<form action=""method="get">
<select name="selectClass">
  <optionvalue="1">一级</option>
  <optionvalue="2">二级</option>
</select>
<input name="classname" type="text"/><input name="" type="submit"/>
</form>
<?php
if ($_SERVER['REQUEST_METHOD'] == 'GET')
{
echo "表单提交";
echo $_GET['selectClass'];
}