PHP javascript表单证验未通过而表单依然提交

PHP javascript表单验证未通过而表单依然提交
如题，我的情况是不输入任何数据，点击提交注册，会弹出“请输入用户名”这样的提示，点击确定后 就转到另一个页面，并只显示一句话：Column 'UserName' cannot be null。
下面是代码：

HTML code

<!--Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/--><?php require_once('Connections/conetion.php'); ?><?phpfunction GetSQLValueString($theValue, $theType, $theDefinedValue = "", $theNotDefinedValue = "") {  $theValue = (!get_magic_quotes_gpc()) ? addslashes($theValue) : $theValue;  switch ($theType) {    case "text":      $theValue = ($theValue != "") ? "'" . $theValue . "'" : "NULL";      break;        case "long":    case "int":      $theValue = ($theValue != "") ? intval($theValue) : "NULL";      break;    case "double":      $theValue = ($theValue != "") ? "'" . doubleval($theValue) . "'" : "NULL";      break;    case "date":      $theValue = ($theValue != "") ? "'" . $theValue . "'" : "NULL";      break;    case "defined":      $theValue = ($theValue != "") ? $theDefinedValue : $theNotDefinedValue;      break;  }  return $theValue;}$editFormAction = $_SERVER['PHP_SELF'];if (isset($_SERVER['QUERY_STRING'])) {  $editFormAction .= "?" . htmlentities($_SERVER['QUERY_STRING']);}if ((isset($_POST["MM_insert"])) && ($_POST["MM_insert"] == "form1")) {  $insertSQL = sprintf("INSERT INTO member (UserName, Password, Email) VALUES (%s, %s, %s)",                       GetSQLValueString($_POST['UserName'], "text"),                       GetSQLValueString($_POST['Password'], "text"),                       GetSQLValueString($_POST['Email'], "text"));  mysql_select_db($database_conetion, $conetion);  $Result1 = mysql_query($insertSQL, $conetion) or die(mysql_error());  $insertGoTo = "index.php";  if (isset($_SERVER['QUERY_STRING'])) {    $insertGoTo .= (strpos($insertGoTo, '?')) ? "&" : "?";    $insertGoTo .= $_SERVER['QUERY_STRING'];  }  header(sprintf("Location: %s", $insertGoTo));}?><meta http-equiv="Content-Type" content="text/html; charset=gb2312"><title></title>