ไม่สามารถลบข้อมูลได้ครับ แต่ลองเอาคำสั่ง sql ไปใช้ดู ก็ลบได้ตามปกติครับ

<script language="javascript">
function fncSubmit()
{
	if(confirm('delete')==true)
	{
		document.form1.submit();
	}
}
</script>

<form method="post" name="form1" action="<?php echo $_SERVER['PHP_SELF']; ?>">
  <input name="num" type="text" maxlength="2" size='4' class="field text fn" required /> 
</form>
  
  <input type='button' name='delete' value=' Delete' OnClick='JavaScript:fncSubmit();'/>

<?php
	if(isset($_POST['delete']))
	{	
		require_once('mysql.php');
		$db = new mysql();

			if($db->DELETE("`student` WHERE `Std_ID` like '%{$_POST['num']}'.'0404%'"))
			{
				if($db->DELETE("`survey_test` WHERE `Std_ID` like '%{$_POST['num']}'.'0404%'"))
				{
					if($db->DELETE("`test` WHERE `Std_ID` like '%{$_POST['num']}'.'0404%'"))
					{
						echo "<script type='text/javascript'>alert('Delete Succesfull')</script>";		
					}
					else
					{
						echo "<script type='text/javascript'>alert('Fail1')</script>";
					}
				}
				else
				{
					echo "<script type='text/javascript'>alert('Fail2')</script>";
				}
			}
			else
			{
				echo "<script type='text/javascript'>alert('" . mysql_error() . "')</script>";
			}
            }
?>

public function DELETE($str) {
		return mysql_query("DELETE FROM $str"); //boolean: success or die
	}